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por fabricio.fagundes publicado 05/05/2018 18h39, última modificação 11/08/2020 16h02

The glossary presented below is a database consisting of information contained in two official glossaries:

  • Glossary of Meteorology of the Center for Weather Forecasting and Climate Studies (CPTEC)
  • Glossary of Meteorology of the Department of Airspace Control (DECEA)



Atmospheric Polarization:  transformation of natural sunlight into polarized light, caused by dispersion in the Earth's atmosphere. 

Absolute:  Refers to the highest or lowest recorded value of a weather element. 

Absorption: The process by which the radiant energy incident on a material is retained by it. The absorbed radiant energy is then transformed into another form of energy, usually heat.

Accumulated rainfall: Accumulated amount of precipitation of any type, mainly of water in liquid state. It is usually the amount measured through a rain gauge.

Accumulated snow : Refers to the amount of snow precipitated in a given period, usually represented in centimeters of snow height.

Accumulation:  Amount of snow or other form of water in the solid state and which is added to a glacier or snowfield per feed.

Adiabatic:  Curve representing in aerodynamic diagram the temperature variations of a small mass of air submitted to a process without exchange of energy with the medium.

Advection : Horizontal transfer of any property of the atmosphere, eg temperature and / or humidity, through air movement (wind).

Aerosol:  Suspension in air or other gas of a set of very fine solid or liquid particles. On such particles the solar rays undergo reflection, refraction or diffusion.

Agglomeration:  Process by which particles grow by collision and by assimilation of cloud particles or other precipitation. 

Air Current Line: lines that are drawn parallel to the direction of the wind to indicate the flow arrangement of the air masses. 

Air Drainage: A  generic term used to indicate the relatively cool airflow, slope below, caused by the action of gravity. 

Air mass : An extensive body of air, along which the horizontal characteristics of temperature and humidity are similar.

Air: A mixture of gases that make up the Earth's atmosphere. The main gases that compose the dry air, and respective contribution percentages, are nitrogen (N2) 78.09%, oxygen (O2) 20.946%, argon (A) 0.93% and carbon dioxide (CO2) 0.033%. Water vapor (H2O) is one of the most important components of air and one of the most important gases in meteorology.

Airbag: Air  mass in which an aircraft loses lift because of strong downward air currents. 

Airep:  altitude data collected by en route commercial airplanes coded and made available by the Aeronautics Command Meteorology Network - REDEMET.

Albedo : Relation between the amount of radiation reflected by the surface of an object and the total of radiation incident on it. The albedo varies according to the properties of the object and is reported in percentage value. Surfaces with high albedo include sand and snow. Forest areas and those newly deforested have reduced albedo.

Altimeter : An instrument used to determine the altitude of an object, relative to a reference level, normally defined from the pressure value at sea level.

Altimeter setting : Pressure value, at a given time and to the mean sea level, programmed on an aircraft altimeter. The knowledge of this value allows the correct determination of the altitude of this aircraft when possible variations in atmospheric pressure.

Altitude : In meteorology, it is the vertical distance between an object and a given reference, represented by constant pressure surface or mean sea level.

Altocumulus : Composed of thick, gray, globular or flat masses, this cloud, of medium height, is basically formed by droplets of water. In mid-latitudes, it is generally found between 2,400 and 5,500 meters (8,000 and 18,000 feet) in height. It is characterized by the frequent presence of a thick, undulating layer, known as "sheep" or "wool flakes". Sometimes confused with clouds of the Cirrocumulus type, its elements (individual clouds) possess greater mass and project shade in other elements. It may form several subtypes, such as Altocumulus castellanus, or Altocumulus lenticularis. Virga also comes from these clouds.

Altostratus : This cloud, of medium height, is basically composed of droplets of water and, sometimes, of ice crystals. In average latitudes, it is found between 4,600 and 6,100 meters (15,000 and 20,000 feet) in height. With shades ranging from white to gray, tallostratus clouds can create a veil or fibrous sheet, often obscuring the sun or moon. Their presence is a good indicator of precipitation and often precedes a storm. Virga often comes from these clouds.

American Meteorological Society : American Meteorological Society. Organization based in the United States, which promotes training and professional advancement associated with atmospheric, hydrological and oceanographic sciences.

Anabastic  front : front in which warm air rises along the surface of discontinuity, above which it lies. 

Active front:  plane bordering between two masses of air in which the air is forced to rise.

Altitude Front: front that exists at higher levels, but does not reach the surface of the Earth. 

Disguised Front: real front whose presence is not readily apparent in the surface synoptic chart given to local radiation influences. 

Anemometer : An instrument used to measure wind speed.

Anemometric level:  height above the ground where the anemometer is actually exposed. 

Aneroid barometer : An instrument used to measure atmospheric pressure. As a result of variations in this pressure, deformations occur in an aneroid (capsule or metal cell, with thin, closed wall, containing vacuum). A graduated display shows the observed pressure.

Angular velocity:  rate of variation of the angle with time in a rotational movement. 

Annual Inequality:  Seasonal variations due to weather causes. 

Adiabatic reason:  index of temperature drop with elevation. 

Absolute Vorticity:  given by the rotational velocity of the absolute velocity. In large-scale dynamic meteorology, it is generally interested only in the vertical component of absolute vorticity.

Anticiclone axis:  in an anticyclone, the line that joins the places of maximum pressure in each level. 

Anticyclone : Area with pressure higher than that presented in surrounding areas, considering the same level. It results in divergent winds, which move counterclockwise in the Southern Hemisphere and clockwise in the Northern Hemisphere. Also known as high pressure area; is the opposite of a low pressure area, or cyclone.

Arctic air mass: A mass of air that develops around the Arctic, characterized by reduced temperatures observed from the surface to high altitudes. The limit of this mass of air is often defined by the Arctic front, characterized by being semi-permanent and semi-continuous. When moving from its region of origin, extending to the south, this mass of air can suffer reduction in height.

Arid Climate:  climatic condition of a certain region characterized by the fact that the rates of evaporation and transpiration are higher than the precipitation.

Arid:  Characteristic of a climate related to the insufficiency of precipitation to maintain the vegetation. 

Atmosphere:  gaseous portion of the physical environment that surrounds a planet. The Earth's atmosphere is situated more or less near its surface by reason of gravity. The atmosphere is divided into: troposphere, stratosphere, mesosphere, ionosphere and exosphere. The atmosphere is three-dimensional. Meteorologists, in a practical way, divide the atmosphere into levels: low levels, near the surface up to 2 thousand meters of altitude, average levels of 3 to 6 thousand meters and high levels above 7 thousand meters. 

Atmospheric Circulation: Atmospheric  movements that extend over a part or the whole of the Earth. This air movement and the wind distribution, considering the average conditions taken over a long period of time, come from different pressure gradients (horizontal) and temperature (vertical), friction forces (surface) and Coriolis (rotation from the earth).

Atmospheric Electricity:  aggregate of several electrical phenomena that occur naturally in the atmosphere. 

Atmospheric movement:  air in motion caused by uneven heating of the atmosphere by the sun. 

Atmospheric Opacity:  power that has the atmosphere to oppose, to some extent, the propagation of light rays. 

Atmospheric pressure : Pressure exerted by the atmosphere at a given point. Its value can be represented in several ways: millibars, millimeters or inches of mercury (Hg), among others.

Autumn : Season between the autumnal equinox and the winter solstice. It is characterized by the reduction of temperatures in the middle latitudes. It occurs in the months of March, April and May in the Southern Hemisphere and in the months of September, October and November in the Northern Hemisphere.

Average daily temperature : The average temperature of a day, considering the average of the hourly readings performed or, more often, the maximum and minimum temperatures observed.

Average latitudes : Range of latitudes, located approximately between the parallels of 35 and 65 degrees, in both hemispheres. This region is also called Temperate Zone.

Average temperature : Average value of the temperatures recorded during a specific period of time. It is often estimated by calculating the mean between the maximum and minimum temperatures. 




Balloon Poll:  Free, unmanned balloon, carrying a set of self-registering meteorological instruments. 

Ballot's Law:  the relationship between the direction of the wind and the location of the high and low pressures that generate it. 

Baroclinic Instability: vulnerability of a planetary flow represented by the jet stream to a synoptic and / or subsymotrical scale disturbance. The instability is due to the horizontal temperature gradient or vertical shear of the flow. The development of medium latitude synoptic systems such as extratropical cyclones is due to this mechanism.

Barotropic instability:  jet current vulnerability to synoptic scale disturbance due to vorticity variation in the jet zone. The kinetic energy of the perturbation increases by receiving the kinetic energy of the basic flow.

Barograph : An instrument used to continuously record atmospheric pressure values, observed by a barometer.

Barometer : An instrument used to measure atmospheric pressure. Two examples are the Aneroid Barometer and the Mercury Barometer.

Barometer of mercury: An instrument used to measure atmospheric pressure. Composed of a long glass tube, open at one end and closed at the other. The tube is filled with mercury and the tube sealed temporarily, depositing it vertically in a tank containing mercury. The downward movement of the mercury in the tube results in the creation of a near-perfect vacuum at its closed end. As the atmospheric pressure increases, the mercury moves from the tank to the pipe; when the atmospheric pressure decreases, the mercury returns to the tank. The height of the mercury column in the tube is the measurement of the air pressure. The first to use the Barometer of Mercury was Evangelista Torricelli (1608-1647), Italian physicist and mathematician, to explain the fundamental principles of hydromechanics. Although mercury barometers are very accurate,

Barometric Pressure : Pressure exerted by the atmosphere at a given point. Its value can be represented in several ways: millibars, millimeters or inches of mercury (Hg), among others.

Beaufort Scale : A system for estimating and reporting wind speed. It is based on the Beaufort Force or Number, composed of wind speed, a descriptive term and visible effects of the wind on the surfaces of the land or the sea. The scale was proposed by Sir Francis Beaufort (1777-1857), hydrographer of the British Royal Navy.

Biometeorology:  Study of the influences exerted on living organisms by the meteorological elements. 

Biosphere:  The biosphere is the transition zone between the Earth and the atmosphere, within which most terrestrial life forms are found, including man, the flora and fauna of the oceans. It is considered the outer portion of the geosphere and the inner or lower portion of the atmosphere. 

Biruta:  Indicator of wind direction, located near the landing field. It consists of a tissue cone with two openings, one of which is larger and coupled to a metal ring. 

Blizzard:  Extremely cold and violent wind accompanied by snow. 

Boiling point : The temperature at which a liquid passes into the gaseous state. Temperature at which the equilibrium vapor pressure between a liquid and its vapor is equal to the external pressure in the liquid. The boiling point of pure water, considering the pressure of an atmosphere, is 100 ° C or 212 ° F.

Bora:  cold, gusty winds blowing during the winter in a southwest direction on the coast bathed by the Adriatic Sea. It blows through Greece from the Balkans.

Breeze:  is the circulation generated by a horizontal gradient of temperature, with the purpose of restoring the balance in this region. 

Bump : Precipitation that starts from a convective cloud, characterized by sudden beginning and end, variations in intensity and by rapid changes in the aspect of the sky. It happens in the form of rain (SHRA), snow (SHSN), or ice (SHPE). It is reported as "SH" in weather observations and in METAR code. 


Calm: Atmospheric conditions devoid of wind or any other air movement. In oceanography, it is the apparent absence of movement of the surface of the water when there is no wind or ripple.

Carbon dioxide (CO2): A heavy, colorless gas that is the fourth most abundant component of dry air, accounting for 0.033% of its total.

Catabatica front : front in which the warm air descends along the surface of discontinuity, above which it is. 

Climatological front:  average geographical position or characteristic of front in a certain region of the Earth. 

Catabático:  Wind blowing from slope below or wind of gravity. 

Cavado axis:  imaginary line in a dug along which the cyclonic curvature of the isobars or contours is a maximum. 

Ceiling : Height of the lowest layer of clouds covering more than half of the sky. If the sky is totally obscure, the ceiling is the height resulting from the quantification of vertical visibility.

Cavado Line:  line that crosses a cyclonic area and that is perpendicular to the course of the cyclone.

Ceiling Lighthouse:  instrument used at night to project a vertical light beam concentrated at the base of the clouds, in order to measure the height of the same with the use of the clinometer. 

Coriolis force:  Apparent force acting on an element of the fluid in displacement on a rotating planet. The Coriolis force acts in the direction perpendicular to the leftward movement of the horizontal movement in the southern hemisphere. It is zero on the equator, negative on the southern hemisphere and positive on the northern hemisphere, reaching extreme values ​​at the poles.

Convergent winds:  two belts of persistent winds, originating from high central subtropical pressure, that blow from the east towards the equatorial ditch. Basically, they are lower level winds characterized by great steering power. In the Northern Hemisphere, the converging winds blow from the northeast and in the Southern Hemisphere, blow from the southeast direction. 

Ceilometer: An instrument used to measure the elevation of the base of a cloud. It can be based on the use of laser, by recording the time it takes for the beam of light emitted to reflect through the base of the cloud and to return to the equipment. Triangulation procedures are applied when using other light sources.

Celestial Vault:  The sky considered under the form with which it apparently arches over the observer's head.

Central Meteorológica:  organ that collects, registers and interprets the meteorological data of a certain area. 

Cerração or Fog:  mass of tiny drops of water suspended in the atmosphere, near or near the surface of the Earth, that reduce the horizontal visibility to less than 1 Km. 

Chance of rain showers:  forecast for rain showers with a confidence of 50% or less.

Circulating cells : Large areas of air circulation created by the rotation of the Earth and the transfer of heat from the Equator to the poles. Circulation is restricted to a specific region, such as the tropics, temperate or polar regions, which influences the type of climate occurring in these regions.

Circulation : Flow or movement of a fluid in or through a certain area or volume. In meteorology, it is used to describe the flow of air when it moves in a pressure system in the atmosphere. It describes smaller patterns in semipermanent pressure systems as well as global air currents of relative permanence. In oceanography, it is used to describe the flow of the water stream within a large area, usually a closed circular pattern as in the North Atlantic.

Cirrucumulu s: Cirrus -shaped cloud with vertical development. It has the appearance of a thin layer of small white balls, generating a wavy effect. It usually creates a "scaly sky," since the ripples can resemble fish scales. Sometimes it is confused with altocumulus, however, it presents smaller individual masses and does not cast shadow on other elements. It is the type of cloud less common and is formed frequently from the clouds cirrus or cirrostratus, with which it is associated in the sky.

Cirrus : One of the three basic forms of cloud (the others are cumulus and stratus). It is also one of three types of high cloud. Cirrus is a thin or thin cloud made up of ice crystals, which often appears in the form of veils or as strands. In mid-latitudes, formations of these clouds are usually found between 6,000 and 9,000 meters (20,000 and 30,000 feet) in height. It is considered as the highest cloud formation, with the exception of the tops of cumulonimbus clouds that occasionally reach greater heights.

Cirrus:  Isolated cloud in the form of delicate white filaments or narrow, white or almost white bands or banks. This cloud has fibrous appearance like hair strands or cock tail. The cirrus is made up of ice crystals. 
* Associated time condition:  Stable time with approximation of areas of instability. Usually at the forefront of the cold front are many cirrus, they are also observed on the cumulonimbus anvil. 

Cirrostratus: Cloud of cirrus format. It develops from the scattering of cirrus clouds, resulting in a thin, regular and whitish layer. It can give the sky a milky appearance or as if covered by a veil. When viewed from the surface of the Earth, the ice crystals present in this cloud can create the halo effect around the Sun or Moon. This cloud is a good precursor of precipitation, indicating its possible occurrence between 12 to 24 hours.

Clear Sky : The state of the sky, when no cloud or obscuration is observed or detected from the observation point.

Clear Sky:  The state of the sky when no cloud or obscuration is seen or detected from the observation point. 

Climate : The historical record and description of the daily and seasonal mean of events associated with the weather, which help to describe a region. Statistics are usually calculated from several decades of observation. The word is derived from the Greek, "klima", meaning inclination and reflecting the importance attributed to the influence of the Sun, by scholars in antiquity.

Climate Forecast:  Numerical prediction of future weather conditions for one and six months, through large scale and low resolution statistical modeling, expressed through positive or negative deviations from past average behavior.

Climatology : The study of climate. It involves the characterization and analysis of the climate, from time series of time variables.

Clinometer: An  instrument used to measure the angular elevation of a light projected at the base of a cloud. Measures the angle of the cloud base included by the observer or equipment, the flashlight and the spotlight illuminated in the cloud. 

Cloud  Luminance : Luminance determined by the amount of light diffused and reflected by the particles that constitute a cloud. 

Celestial Light:  emission of almost permanent radiation by the gases of the high atmosphere that can be distinguished at night and which is presumed to exist during the day.

Cloud : A visible set of tiny particles of matter, such as water droplets and / or ice crystals, in the air. A cloud forms in the atmosphere as a result of the condensation of water vapor on condensation nuclei.

Cloud Bank: A  continuous system of clouds of the same genre and substantially of the same level, but covering only a small fraction of the celestial vault. 

Cloud Barrier: A  compact mass of clouds that appears on the horizon with the approach of an intense tropical cyclone, a wall of clouds, a wall of clouds. 

Cloud Sheet:  particular arrangement of clouds forming a continuous and relatively thin layer of great horizontal extent. 

Cloud Veil:  cloud cover, completely transparent, allowing the perfect location of the sun or moon. 

Cloudiness:  part of the sky covered by a layer of cloud. The concept starts from the span of the celestial vault in eight eighths. 

Cloudy : A condition in which full coverage of the celestial vault occurs through a layer of clouds. The concept results from the division of the celestial vault in eight eighths, considered in the sum of the area covered by clouds, for a specific layer.

Cloudy predominance : A condition in which five to seven octaves cover the celestial vault by a layer of clouds. The concept results from the division of the celestial vault in eight eighths, considered in the sum of the area covered by clouds, for a specific layer.

Cloudy System: distinct and durable grouping of clouds, generally comprising spannersas differentiated zones denominated of "nebulous sectors", congregating them of characteristic way and in each one of which the general aspect of the sky as a whole presents / displays remarkable peculiarities. 

Coalescence : Fusion of two drops of water into a single larger drop.

Cold : A condition marked by a temperature below or below its normal temperature. No heat.

Cold Advection : Horizontal transfer of the property of the atmosphere, through the displacement of air with temperature below the temperature present in the destination.

Cold front: The front end of a mass of cold air moving under a mass of warm air, displacing it from its path. Generally, with the passage of a cold front, the temperature and humidity are reduced, the pressure rises and the wind changes direction (usually from the southwest to the northeast in the Southern Hemisphere). Precipitation usually precedes or succeeds the cold front, and very quickly, a storm line can anticipate the front.

Cold Wave : Rapid temperature drop over a 24-hour period and requires special care in agriculture, industry, commerce and social activities.

Comma Cloud: A  subsymothetic scale disorder that forms at low or medium levels within the mass of cold air. These systems, typical of winter, can cause intense rains even when they are formed on the continent.

Condensation : A process by which the water vapor passes from the gaseous state to the liquid state. It is the physical process opposite to evaporation.

Condensation nuclei : Small particles in the air. Its presence allows the condensation of water vapor in the atmosphere, resulting in the formation of water droplets.

Conduction : Heat transfer through a substance, through molecular action or heat transfer resulting from contact between two substances.

Confluence:  is a characteristic of the flow in which the current lines come together or approach. Difluence is the opposite feature.

Convection: Movements in a fluid, responsible for the transportation and mixing of its properties. These properties can be heat and / or moisture. When used to indicate only upward vertical movement, it is the opposite of subsidence.

Convective System: shows the short-term forecast, hours in advance and the evolution of the convective systems. This product allows monitoring the evolution of the convective systems, usually associated with heavy rains, as well as the intensification and direction that the system can follow. 

Convergence : Wind movement associated with horizontal air flow into a specific region. Convergence at lower levels is associated with upward air movement. Opposite of divergence.

Coordinates:  used in meteorology are georeferenced. At any point in the atmosphere or ocean, the x-axis, y and z point in the directions east, north, and vertically upwards. That is, the z-axis points in the opposite direction of gravity. The x, y, z axes measure the distances in their respective directions. 

Coriolis effect : A force per unit mass that derives only from the Earth's rotation and acts as a deflection force. It depends on the latitude and speed of the moving object. In the Southern Hemisphere, air drifts to the left of its trajectory, while in the Northern Hemisphere it deflects to the right. The force is maximum in the poles and almost null in the Equator.

Cover:  word often used to indicate the point of temperature inversion. The air at the point of inversion is warmer and lighter than the stable, dense, colder air below, and so it acts as a cover preventing the lower air from rising. 

Crest : Elongated area of ​​high atmospheric pressure, associated with an area of ​​maximum anticyclonic circulation. It's the opposite of Cavado.

Cumulunimbus : Cloud resulting from the vertical development of cumulus cloud, often covered by an anvil element. Also called storm cloud, it is often accompanied by heavy showers of rain, lightning, thunder and sometimes hail, strong gusts of wind and tornadoes.

Cumulus: One of the three basic forms of cloud (the others are cirrus and stratus). It is also one of two types of low cloud. It is a cloud with vertical development, with flat bases and superior surfaces in the form of dome or cauliflower. The base of the cloud is often below 900 meters (3,000 feet), but the height of the top can vary. Small, sparse cumulus clouds are associated with good weather (cumulus humilis). With additional surface warming, they can develop vertically throughout the day, with the top of this cloud easily reaching 6,000 meters (20,000 feet) or more in the troposphere. Under specific atmospheric conditions, these clouds can become larger clouds known as cumulus congestus and can produce rainfall.

Cyclogenesis : A process that creates a new system of low pressure, or cyclone, or intensifies a pre-existing system.

Cyclone: Area with pressure lower than that presented in surrounding areas, considering the same level. It results in a convergence of winds, which move clockwise in the Southern Hemisphere and counterclockwise in the Northern Hemisphere. Also known as low pressure area; is the opposite of a high pressure area, or anticyclone.

Cyclonic wave:  rippling over a front in a synoptic surface chart. 

Cyclotrophic Balance:  is a balance between gradient, pressure and centrifugal forces. This balance is feasible when Coriolis force and friction are absent or negligible. For small-scale rotational motions such as swirls and tornados the cyrotrophic balance is a good approximation.



Defrost:  melting of snow or ice, or both, to the surface of the Earth, as a result of raising the temperature above 0ºC. 

Density: Ratio between mass of a substance and the volume it occupies. In oceanography, it is equivalent to the specific gravity and represents the ratio of the weight of a given volume of seawater to the weight of the same volume of distilled water at 4.0 degrees Celsius or 39.2 degrees Fahrenheit.

Depression : Used as a synonym for terms: low pressure, low or dug system. It also applies to a development phase of a tropical cyclone, known as tropical depression, to distinguish this phenomenon from other synoptic features.

Dew : Condensation, in the form of small drops of water, that accumulates in the grass and in small objects near the ground. This condensation usually occurs at night, when the temperature drops, reaching the dew point.

Dew point : Temperature at which saturation of the water vapor contained in a portion of air occurs. The temperature of the dew point is always less than or equal to the air temperature.

Diffraction Phenomenon:  image of interference produced within the geometric shadow projected by an object due to bending, by an amount that varies with the length of the light waves encountering obstacle. 

Diffuse  illumination : illumination without any direct contribution of solar radiation. 

Diffuse Lightning:  type of lightning associated with an entire discharge. 

Disturbance:  This term can be applied to an area of ​​low pressure, or cyclone small in size and influence or to an area that is exhibiting signs of cyclonic development. Favorable region for the occurrence of storms.

Difluence:  a characteristic of the flow in which the lines of chain move away or fork down stream. Opposite Confluence.

Deluge:  fall of torrential rains that cause flooding of affected areas. 

Directional Shear : Gust created by an abrupt change in direction of the wind with height.

Disturbance : This term has several applications. It is used to describe an area of ​​low pressure, or cyclone, with small or insignificant dimensions. It can also be used when an area is exhibiting signs of cyclonic development. The term is also used to define a phase of development of a tropical cyclone, known as tropical disturbance, to distinguish it from other synoptic phenomena.

Discontinuity Line:  line of thunderstorms marking the position of a moving front. 

Dissipation:  decrease or disappearance of a meteorological condition, such as fog, clouds, etc. Diffusion by the introduction of different conditions. 

Divergence : Wind movement associated with horizontal air flow out of a specific region. Divergence at lower levels is associated with downward movement of air. Opposite of convergence.

Drying : Overly dry weather in a specific region. It must be sufficiently long so that the lack of water causes a serious hydrological imbalance.

Doppler radar : A weather radar that detects the direction of travel and speed of moving objects. Precipitation drops can be detected by the weather radar and their horizontal displacement (drift or approach) can be determined. The velocity of the particles is measured using the Doppler effect. The radar was named in honor of the Austrian physicist J. Christian Doppler who in 1842 explained the reason why the whistle of a train, when approaching, is sharper than the same whistle, when the train departed.

Drizzle : Precipitation that falls slowly in the form of tiny drops of water, with diameters smaller than 0.5 millimeters. It comes from stratus clouds and is often associated with low visibility and fog. It is referred to as "DZ" in weather observations and in METAR code.

Dry  climate : climate, excessively dry in a specific region. It must be sufficiently prolonged so that the lack of water causes a serious hydrological imbalance.

Dry Bulb Thermometer: Thermometer used to measure the ambient temperature. The recorded temperature is considered equivalent to the air temperature. One of the two thermometers that make up a psychrometer.

Dry mist : Suspension of fine dust particles and / or smoke in the air. Invisible to the naked eye, the particles reduce visibility and are numerous enough to give the air an opaque appearance. It is referred to as "HZ" in weather observations and in METAR code.

Dug : Elongated area of ​​low atmospheric pressure which is associated with a minimal cyclonic circulation area. Opposite of Crista.

Duplicatus:  banks, sheets or layers of overlapping clouds at slightly different levels, sometimes partially welded together. This term applies mainly to cirrus, cirrostratus, altocumulus, altostratus and stratocumulus.

Dust : Small particles of earth or other matter, suspended in the air. It is referred to as "DU" in meteorological observations and by METAR.



Eastern Wind : Term applied to the extensive patterns of persistent winds, with predominant element of east, like the trade winds.

Ecuador : Geographic circle at zero degrees of latitude on the Earth's surface. It is the imaginary line that divides the planet into the Southern Hemisphere and the Northern Hemisphere, being equidistant from the South and North poles.

El Niño : Cyclical temperature warming of the sea water in the eastern Pacific Ocean and the western coast of South America, which may result in variations in the weather patterns in various regions of the planet. This phenomenon occurs when hot equatorial waters displace cooler waters of the Humbolt Current, interrupting its ascension process.

Electrojet:  current of electricity that moves in the upper atmosphere around the Equator and the polar regions, where the appearance of the auroras takes place. 

Eletrometeoros:  is a visible or audible manifestation of the atmospheric electricity. They may occur in the form of discontinuous electric discharges such as lightning and thunder or more or less continuous phenomena such as San Telmo fire, polar aurora, etc. 

Elevation of the station : Vertical distance from the mean sea level, which is the reference level for all atmospheric pressure measurements at that station.

Eolipila:  metal ball to demonstrate the generation of the winds.

Equatorial calms:  name given to a region in the tropics where, from time to time, the winds are very light for weeks. In sailing times, ships were kept in calm or equatorial calms for long periods, because there was no wind that filled the sails. They are located on both sides of the Equator, between the two waists of the trade winds. Its exact position varies from month to month, being more to the North in June than in December. The climate of this region is hot and humid with misty skies, very variable light winds, many thunderstorms, calms and storms. 

Equatorial dug:  elongated area of ​​low atmospheric pressure which is associated with a minimal cyclonic circulation area. Opposite crest. 

Equinox : Point at which the ecliptic intercepts the celestial equator. Days and nights are almost equal in duration. In the Southern Hemisphere, the spring equinox occurs around September 22 and the autumn equinox around March 20.

Estimated Satellite Rain:  Indicates the rains that occurred during the last 24 hours observed by the meteorological satellite. 

Evaporation : Physical process through which a liquid passes into the gaseous state. It is the physical process as opposed to condensation.

Evapotranspiration : The total water transferred from the surface of the Earth to the atmosphere. It consists of evaporation of water, originally in liquid or solid state, plus the transpiration of plants.

Extratropical Cyclone : Any cyclone of non-tropical origin. Generally considered as a migratory frontal cyclone, found in medium and high latitudes.

Eye wall : An organized convection band, which surrounds the eye, or center of a tropical cyclone. Contains cumulonimbus clouds, heavy rain and high speed winds.

Eye:  center of a tropical storm or hurricane, characterized by a more or less circular area of ​​clear winds and sparse rains. An eye will normally develop when the wind speed exceeds 124 km / h. It can range in size from 8 to 96 kilometers, but the common size is 32 kilometers. In general, when the eye begins to shrink, the storm is intensifying. 



Fahrenheit Temperature Scale: Temperature range at which water at sea level has a freezing point at 32 ° F and a boiling point at 212 ° F. Most commonly used in areas that adopt the English system of units. Created in 1714 by Gabriel Daniel Fahrenheit (1696-1736), a German physicist who also invented the alcohol and mercury thermometers.

Flashlight: An  instrument consisting of a drum and an optical system that project a narrow, vertical band of light on a cloud base. 

Flickering:  consists of rapid, often pulsating, variations of light from stars or from terrestrial light sources. It is similar to tremulin. 

Foehn:  dry wind with strong downward component, hot for the season and characteristic of many mountainous regions. The air is cooled dynamically when climbing mountains, however, this leads to condensation that holds the temperature drop by releasing the latent heat. 

Fire of S. Telmo: light electric discharge into the atmosphere, more or less continuous, of weak or moderate intensity, which starts from objects high on the surface of the globe as lightning rods, wind vane, masts of ships. It often appears in the form of greenish tufts, clearly visible at night. 

Fog: Aggregate of tiny water droplets, suspended in the atmosphere, which forms near the surface of the Earth, reducing the horizontal visibility to less than a thousand meters. It is formed when air temperature and dew point become close, or equal, and when sufficient condensation nuclei are present. It is referred to as "FG" in weather observations and in METAR code.

Forecast: Description of expected future occurrences. The weather forecast includes the use of mathematical models based on atmospheric parameters, associated with the skill and experience of meteorologists.

Forecast Chart:  Forecast represented, graphically, for a fraction of the airspace. 

Fracto:  prefix applied to the formation of clouds and means "torn by the wind". 

Freezing : One of the processes associated with the transformation of the state of a substance. In this case it passes from liquid state to solid state. It is the opposite of fusion.

Freezing point : The temperature at which a liquid passes into the solid state. Pure water freezes at 0 ° C or 32 ° F under one atmosphere pressure. When salt concentration rises, the freezing point of the water decreases.

Frequency:  expresses the number of cycles per unit time. 

Friction:  is the force that opposes relative motion between two adjacent blades of the fluid or between the fluid and the rigid walls containing the fluid. When the relative motion is zero, the frictional force is also zero.

Front passage: It is the passage of a front over a specific point on the surface. It is perceived by variations in dew point, temperature, atmospheric pressure and wind direction. When passing a front, clouds and precipitation may occur.

Front: Transition zone or contact surface between two air masses of different densities, which usually implies different temperatures. For example, the area of ​​convergence between hot and humid air and cold and dry air. 

Frontal System:  Classic front system, usually composed of cold front, hot front and low pressure center on the surface called cyclone. 

Frontal System:  front system delineated on a synoptic surface chart; more particularly, a complete system belonging to a specified frontal depression. 

Frontal Zone:  atmospheric transition layer separating two masses of air and in which the properties are intermediate between the masses of air involved. 

Frontogenesis : Birth or creation of a front. It happens when two adjacent air masses, having different densities and temperatures, are found by the action of the winds, creating a front. It can happen when one of the air masses, or both, exhibits their original enhanced properties, by moving on a surface. It is common in southern Brazil and northern Argentina. Opposite of Frontolise.

Frontolysis: The end or "death" of a front, when the transition zone no longer presents the same contrast of properties observed previously. Opposite Frontogenesis.

Frost Point:  maximum temperature of white frost formation by sublimation, originating from the atmospheric humidity on a polished and cold surface. 

Frost:  deposition of crystalline ice on exposed surface in the open air, resulting from the freezing of water vapor in the air near the surface.

Fujita Intensity Scale:  Scale to classify tornadoes according to the speed of rotational winds and the damage caused by tornadoes. 

Fuzzy Front:  front whose presence in the surface synoptic chart is difficult to determine after the studies of the meteorological elements. The contrast between the elements close to the front is weak and the width of the frontal zone is large. 



Gallop:  vibrations caused by wind and ice formation on transmission lines. 

Garoa:  regional expression of Brazil, mainly of São Paulo, to express drizzle. 

Geopotential:  potential energy of a portion of the air of unit mass, and its reference value of zero is, in general, in the average level of the sea. 

Geostrophic:  wind blowing parallel to the isobars. 

Glory: consisting of one or more series of colored rings which the observer sees around his own shadow projected onto the fog, dew, or on a cloud composed of numerous small particles. The colored rings are due to diffraction of the light and have the same arrangement as the crown. 

Gradient:  vector operator. The orientation of the gradient is the direction in which the variable is oscillating with the highest rate and its modulus is precisely this rate. 

Geopotential Trend: Geopotential  variation with time in a given location. The geopotential trend equation is an important tool for weather forecasting.

Geostationary Satellite: Meteorological satellite that maintains the same position relative to Ecuador, when the Earth rotates. They can be exemplified by GOES series satellites, acronym for Geostationary Operational Environmental Satellite.

Geostrophic Balance:  is a balance between the forces of gradient, pressure and Coriolis. This swing is feasible only when other forces like centrifugal and friction are absent or negligible. 

Geostrophic Wind:  defined as uniform and stationary wind tangential to the straight and parallel isobars in an atmosphere without friction. It is proportional to the pressure gradient. The Coriolis force acts to the left and the force of the pressure gradient acts to the right of the geostrophic wind in the Southern Hemisphere. The two forces being in perfect balance, the portions of the air do not suffer acceleration. Far from surface and orographic barriers and far from pressure centers, where isobars have large curvatures, the wind observed on the synoptic scale in the middle latitudes is roughly geostrophic.

Goal: Acronym for Meteorological Aerodrome Report. It is a coded report, associated with meteorological observations and used to provide information about surface weather conditions. It usually consists of the following items: wind, visibility, visual range, present time on the track, cloudiness, air temperature and dew point and pressure at sea level (altimeter adjustment).

Good Weather: Subjective weather description. Considered as pleasant weather conditions for a given time of year and physical location.

Grade: A measure that represents a single division, or unit, on a temperature scale.

Grosswetterlage:  mean pressure distribution over a period of time, during which the essential characteristics of the atmospheric circulation remain approximately invariant over a wide region. 

Guidance:  influence exerted in the direction of the movement of disturbances of low levels by the currents of air of the highest levels.

Gradient  flow : flow without horizontal friction in which isobars and flow lines coincide. 

Greenhouse effect: Natural phenomenon associated mainly with the presence of carbon dioxide and water vapor in the atmosphere. These gases allow the sun's rays to pass through the atmosphere, but prevent part of the resulting heating from returning into space. As a result, there is a rise in temperature observed in the lowest part of the atmosphere.

Greenwich mean time: Convention used to identify reference time on the planet, defined from Zero time zone. This spindle covers the reference meridian, which passes through Greenwich, England, where this method of world time division was initially used. According to the method, the globe is divided into 24 time zones of 15 degrees arc, or distant an hour apart. East of the Greenwich meridian, the spindles range from one to 12 hours, preceded by the negative sign (-), indicating the number of hours to be subtracted to obtain Greenwich Mean Time (GMT). To the west, the time zones are from one to 12 hours, but are preceded by the positive sign (+), indicating the number of hours to be added to obtain the TMG.



Hail : Precipitation that originates from convective clouds, like cumulonimbus, and that falls in the form of spheres or irregular pieces of ice, being able to occur in different sizes and forms. Hail has a diameter equal to or greater than five millimeters. Smaller ice chunks are classified as small ice balls, small snowballs, or "graupel". Individual elements are called stones. It is referred to as "GR" in weather observations and in METAR code. Small hail or small snowballs are referred to as "GS".

Hail Storm:  storms that occur only with the presence of large cumulonimbus clouds and are produced by fast rising and falling air currents that reach up to 30 or 40 knots. 

Hail:  more or less oval ice rocks varying in diameter of 5 mm or more. They may fall apart or in irregular blocks. They are composed of glazed ice or opaque and light layers alternately; they originate in cumulonimbus clouds. Surface temperatures are usually above 0 ° C. 

Half  burr: in wind plotting in weather charts the half burr is indicative of the speed of a wind of 5 knots. 

Halo : Common name for luminous meteors consisting of circles or bright arcs, centered by the Sun or Moon.

Hangover: Elevation of sea level, comparing to periods of non-occurrence of storms. Although the more dramatic elevations are associated with the presence of hurricanes, less intense low-pressure systems may result in a slight rise in sea level if the wind favors this condition. It is calculated by subtracting the normal astronomical tide from the tide observed in a storm.

Heat: The form of energy transferred between two systems by virtue of a difference in temperature. The first law of thermodynamics demonstrates that the heat absorbed by a system can be used to perform work or to raise the internal energy of this system.

Heat Index: combination of air temperature and humidity that describe how the temperature is felt. This is not the current air temperature. 

Heat wave: Period of time excessively hot, resulting in discomfort or damage to health. It can last for several days or several weeks. It occurs in large areas, on a synoptic scale.

High latitudes: Range of latitudes, located approximately between the parallel of 60 and 90 degrees, in both hemispheres. This region is also called the Polar Region.

High Latitudes:  Range of latitude located approximately between 60 and 90 degrees north and south. Also called the polar region. 

High pressure system : Area with pressure higher than that presented in surrounding areas, considering the same level. It results in divergent winds, which move counterclockwise in the Southern Hemisphere and clockwise in the Northern Hemisphere. Also known as high pressure area; is the opposite of a low pressure area, or cyclone.

High:  is the region of relative high pressure compared to the neighborhood on the same horizontal level. 

Hot advection: Horizontal transfer of property of the atmosphere, through the displacement of air with temperature higher than the temperature present in the destination locality.

Hot front: The front end of a mass of hot air that, when moving forward, replaces a mass of cooler air. Generally, with the passage of a hot front, temperature, humidity and atmospheric pressure rise and, although the winds change direction (usually from the southwest to the northwest in the Northern Hemisphere), the passage of a hot front does not is as pronounced as the passage of a cold front. Precipitation, in the form of rain, snow, or drizzle, usually precedes the front, as well as convective and temporal rains. The occurrence of fog is common in areas of cold air preceding the hot front. Although the atmosphere is generally clear after the passage of this front, some conditions associated with the presence of hot air can result in fog.

Humidity: Concerns the amount of water vapor in the air. It is often mistaken for relative humidity or dew point.

Hurricane : The name given to tropical cyclones with continuous winds of 120km / h (65 knots), occurring in the North Atlantic Ocean, Caribbean Sea, Gulf of Mexico and in the north-eastern Pacific Ocean. This same tropical cyclone is known as a typhoon in the western Pacific and as a cyclone in the Indian Ocean.

Hurricane alert: Formal note released by the National Hurricane Center (NHC). This communication, accompanied by recommendations, is disclosed when the analysis of atmospheric conditions indicates that coastal areas and / or group of islands are potentially under threat of hurricane in the period between the next 24 and 36 hours. Hurricane Warning is used to inform the general population as well as specific interests about the storm's location, intensity, and displacement.

Hurricane Warning: A formal note issued by the National Hurricane Center (NHC). This communication, accompanied by recommendations, is released when analysis of atmospheric conditions indicates that coastal areas and / or group of islands will be potentially under hurricane threat within the next 24 hours. The Hurricane Warning is used to inform the general population as well as specific interests about the storm's location, intensity, and displacement.

Hydroestimator: a  method that uses an exponential empirical relationship between the estimated radar precipitation and the brightness temperature of the cloud top, extracted from the infrared channel of the GOES-12 satellite, generating real-time precipitation rates, that is, done automatically . 

Hydrometeoro:  meteorological phenomena resulting from changes in the state of water vapor in the atmosphere. They can occur in the following forms: precipitation as rain, drizzle, snow, hail; virga; particles more or less suspended in the atmosphere like fog, mist; deposits such as dew, frost, porous ice, glassy ice. 

Hydrometeorology:  branch of meteorology that is related to hydrology. 

Hydrosphere: parts of the Earth's surface made up of water and ice. 

Hair Hygrograph:  instrument that provides a continuous record of relative humidity. Human hair free of oil or fat, changes its length as a function of relative humidity. Through a system of levers, the change in hair length is amplified and recorded by a pen on a chart affixed to a cylinder running in uniform motion. 

Hygrometry:  part of the physics that determines the amount of water vapor contained in the atmosphere. 

Hygrometer:  instrument used to measure the moisture or moisture content of water in the atmosphere. 

Hodograph: lines joining the extremities of the vectors they represent in polar coordinates, wind velocities at altitudes and at successive levels.

Hydrographic basin: a  region drained by one or all of one or several watercourses.



Ice: Solid form of water. It can be found in the atmosphere in various forms: ice crystals, snow, small ice balls, hail, among others.

Ice Prisms:  Falling of unbranched ice crystals, in the form of needles, prisms or scales, often so small that they appear to be suspended in the air. They may fall from a cloud or clear sky. 

Ice Storm:  intense formation of ice on objects caused by cooling. 

Inches of Mercury:  name that comes from the use of mercurial barometers that compare the height of a column of mercury with the pressure of the air. 

Images of satellites : Images acquired by satellites that reveal, among others, information associated with the flow of water vapor, movement of frontal systems and the development of a tropical system. The animation of these images helps the meteorologists in the elaboration of weather forecasts. Some images are acquired using the visible portion of the light, with acquisition restricted to the daytime period. Others result from sensitivity to infrared thermal radiation, indicating the temperature of the clouds, and can be acquired day or night.

Incus:  upper portion of the cumulonimbus that expands in the form of an anvil, having fibrous, smooth or striated appearance. 

Instrument or meteorological shelter:  A ventilated box structure designed to protect instruments measuring, for example, temperature, pressure, direct sun exposure, rainfall and condensation. 

Infiltration: movement of surface water entering the soil. The infiltration is equal to the total precipitation minus the losses caused by plant uptake, retention in soil surface depressions, evaporation and surface runoff. 

Isotherm: is the surface at which the temperature is constant. In a horizontal plane the isotherms are lines that pass through the points of equal temperature. That is, on one side of the isotherm the temperature is higher than on the other side.

Interchange:  mixing of characteristics between two or more air masses. Terms are generally applied to the mixture of polar and tropical air masses. 

Instability Line:  cumulus and cumulonimbus cloud formation region in a continuous line format. The wind can rise abruptly, the temperature drops suddenly accompanied by showers of rain and hail, and often by lightning and thunder. Generally, the fronts precede or succeed. 

Intertropical Convergence Zone: Area where trade winds from the Northern and Southern Hemispheres converge. Generally, it is located in the region comprised by the parallel of 10 degrees, to the north and south of the Equator. It is an extensive area of ​​low atmospheric pressure where both the Coriolis effect and the atmospheric pressure gradient at low levels are negligible, occasionally allowing for the formation of tropical disturbances. Its average position varies according to the area of ​​highest incidence of solar radiation. Thus, during the winter in the Southern Hemisphere, the ITCZ ​​moves northward over the southern North Atlantic and South Asia.

Inversion: Concept associated to the non-occurrence of the usual pattern of variation of an atmospheric property as a function of altitude. Usually, it refers to the elevation of temperature as a function of an increase in altitude. In this case, this behavior is the inverse of the usual temperature decline, observed in higher dimensions.

Irisations: are colors that appear in the clouds, sometimes mixed together in the form of bands, roughly parallel to the edges of the clouds. Green and pink predominate, often with a pastel tint. The lines of separation between the colors do not form circles with the Sun in the center but rather bands that accompany the contours of the cloud. 

Isobara:  surface at which atmospheric pressure is constant. In a horizontal plane the isobars are lines passing through points of equal pressure. That is, one side of the isobar pressure is larger than the other side. 

Isotherm:  surface on which the temperature is constant. In a horizontal plane the isotherms are lines that pass through the points of equal temperature. That is, one side of the isotherm temperature is larger than the other side. 

Inversion Layer Atmospheric layer in which the temperature increases with increasing height. 

Isolated  rains: rains distributed spatially by some localities of a certain area.



Jet stream: Area of ​​high winds concentrated in a relatively narrow range in the upper troposphere in mid and subtropical regions of the Southern and Northern Hemispheres. Flowing in a semi-continuous band around the globe from west to east, Jet Currents are caused by variations in air temperature when cold polar air, which moves to the Equator, encounters warm equatorial air, which is moving to the poles. They are marked by a high concentration of isotherms and by an intense vertical shear. 


Kelvin Temperature Scale: Temperature range at which water at sea level has a freezing point of 273 K and a boiling point of 373 K. It is mainly used for scientific purposes. Also known as Absolute Temperature Scale. Presented in 1848 by William T. Kelvin (1824-1907), Scottish physicist and mathematician.

Khamsin:  hot dry wind blowing south in Egypt, along the Mediterranean, similar to sirocco and generally in March, April and May.  


La Niña:  period of intensification of the winds and abnormal cooling of the surface in the center and east of the Tropical Pacific. Or opposite of El Niño.

Latitude: Angular measure, in degrees, between the plane of the Equator and the normal one at any point on the reference ellipsoidal surface. It is often represented graphically by lines that are distributed parallel to the Equator, towards the north and south poles, located at 90 degrees, in relation to the Equator.

Leeward Slope:  part of the slope of a hill or mountain or region, sheltered from the wind as a result of a terrain accident. 

Lénard effect:  separation of electric charges in the precipitation of rain caused by the rupture of the droplets of water, making these droplets positively charged and the air negatively charged. 

Lightning Channel:  Irregular path through the air, along which lightning strikes. 

Lightning in Ball:  fireball that sometimes appears after a lightning bolt.

Lightning: it is the luminous manifestation that accompanies the momentary discharge between two clouds with electric charges or between a cloud and the ground. 

Lightning of Heat: lightning at a distance that can be observed as a brief clearing near the horizon, the sky or a cloud. 

Litometeors: meteor consisting of a set of particles most of which is solid and non-aqueous. The particles are more or less suspended in the air or are lifted from the ground by wind such as dry haze, haze of dust, smoke, dust or sand cloud, storm of dust or sand, swirl of dust or sand. 

Longitude: Angular measure, in degrees, between the plane of a reference meridian and the meridian plane passing through any point on a reference ellipsoidal surface. It is often represented graphically by lines that circle the planet, passing through the north and south poles. The distance between these lines is higher in Ecuador and lower in higher latitudes. Time Zones are related to longitude.

Low Latitudes:  belt located between 0 (zero) and 30 degrees latitude, both north and south of Ecuador. Also called a tropical or torrid region. 

Low latitudes: Range of latitudes, located approximately between parallels of 0 and 30 degrees, in both hemispheres. This region is also called the Tropical or Torrid Region.

Low pressure system: Area with pressure lower than that presented in surrounding areas, considering the same level. It results in a convergence of winds, which move clockwise in the Southern Hemisphere and counterclockwise in the Northern Hemisphere. Also known as low pressure area; is the opposite of a high pressure area, or anticyclone.

Low Troposphere Poll:  The low troposphere polls refer to meteorological conditions up to 3,000 meters in general, with special emphasis on the boundary layer. 

Low: it  is the region of relative low pressure compared to the neighborhood on the same horizontal level. 

Luminance: the  quotient of the intensity of light emitted in a given direction by the projection of the area of ​​a luminous emitting surface on a plane perpendicular to that direction. 

Luminous Projector: An instrument consisting of a drum and an optical system that projects a narrow, vertical beam of light onto the base of clouds.

Luminous Flux:  characteristic amount of radiant flux and expressing its ability to produce luminous sensation. 

Lump:  accumulations of ice crystals that remain separated or just frozen with each other. They form a thin layer giving the surface of the sea a gray or lead color.  


Maestro:  wind blowing SE in the Adriatic Sea, in general, in winter and spring. 

Meso-scale: Scale of meteorological phenomena ranging from a few kilometers to about one hundred kilometers. This includes Mesoscale Convective Complexes, Mesoscale Convective Systems and wind gusts. Smaller phenomena are classified as of Microscale, while those of greater extension are classified as of Scale Synoptic.

METAR Code: Code  code for weather report messages. 

Meteogram: are graphs of a certain point, grid of the model, of the forecast of the main meteorological elements used in the forecast. The graphs of each meteorological element consists of a red header that carries the name of the variable and the unit of measurement, the vertical dotted lines indicates the 00Z point of the day, the horizontal lines are the scale of each weather element.
Ex: Header: provides information about the center responsible for the model (MCT / INPE CPTEC); type of model (regional model); date and time of the model initial condition data (24AUGs 2005, 00Z); day, month, year and time zulu; locality, city, State, BR (Alto Tietê, SP, BR); country, latitude and longitude (51.22W - 30.02S and altitude 0 m).

Meteor:  any phenomenon other than a cloud, observed in the atmosphere or on the surface of the Globe. There are 4 types of meteors: Hydrometeors; Litometeoros; Photometeoros; Electrometeoros. 

Meteorological Balloon:  are simple balloons, similar to a toy balloon, but made of sturdy material. The weather balloons carry a small automatic radio transmitter called radio-probe. It is connected to instruments that measure temperature, humidity, pressure, etc. As the balloon rises, it registers and transmits the measurements taken at different heights (order of 20 to 40 thousand meters) above the surface of the Earth. Radio probes can also be tracked by radar and thus wind speed and direction can be calculated at different heights of the atmosphere. Normally the balloon will burst and then the radio-probe will fall off with the help of a small parachute. 

Meteorological data:  atmospheric information (temperature, pressure, wind, humidity, rain, solar radiation, etc.) from satellite sensors, commercial airplanes, merchant ships, surface and altitude meteorological stations, and weather radars.

Meteorological elements:  we can consider as: pressure, temperature, cloudiness, humidity, precipitation, direction and wind speed, etc. 

Meteorological Front:  region that delimits two masses of air with distinct characteristics, causing certain meteorological phenomena like clouds, precipitation, turbulence, etc. 

Meteorologist: Scientist studying the atmosphere and atmospheric phenomena.

Method of Analogies:  a prediction method based on the hypothesis that the current synoptic situation evolves in the same way that an analogous situation would evolve in the past. 

Meteorology: Science that studies the atmosphere and its associated phenomena. Among the various fields of study, the synoptic, physical and dynamic meteorology can be mentioned; meteorology applied to aeronautics and marine, agrometeorology, hydrometeorology, micrometeorology and numerical forecasting.

Micro-barograph: An instrument used to continuously record small variations in atmospheric pressure values, observed by a barometer.

Microburst: A convective downdraft (downburst) that covers an area less than 4 km along a side with peak winds that last 2–5 minutes.

Differential velocity across the divergence center is greater than 10 m s−1. The strong wind shears associated with a microburst can result in aircraft accidents. Microbursts can be wet (contain rain) or dry.

Milibar: Unit of measurement for atmospheric pressure. One millibar (mb) is equivalent to normal 0.750mm of mercury or 100 newtons per square meter. The standard atmospheric pressure at the earth's surface is 1,013.2 millibars.

Millimeters of mercury (Hg): Term derived from the use of mercury barometers, which associate the height of a column of mercury with atmospheric pressure. One millimeter of mercury is equivalent to 1.33 millibars or 0.039 inches of mercury.

Millimeters:  measure of precipitation.

Mirage:  optical phenomenon constituted mainly by fixed or undulating images of distant objects.

Meteorological Forecast Models: spanididos in 2 types, they are: Regional Model - ETA: the ETA model is a meso-scale model, in point of grid, of primitive equations. The version of the ETA model that runs operationally at CPTEC is hydrostatic and covers most of South America and adjacent oceans. The current horizontal resolution is 40 km and the vertical 38-layer resolution. Predictions are provided twice a day, one with initial condition at midnight and another at 12 o'clock UTC. Global Model - MCGA: Model of General Circulation of the Atmosphere. The version of the Global model that runs operationally at CPTEC covers the entire Globe. The current horizontal resolution is 100 km. Predictions are provided twice a day, one with initial conditions at midnight and another at 12 a.m. UTC.

Monsoon:  wind from the general circulation of the atmosphere characterized by the seasonal persistence of a given wind direction and a marked variation of this direction from one season to the next. 

Mutatus:  term used when all or a large part of a cloud undergoes a complete internal transformation, thus becoming from one genre to another. This is the case, for example, of stratus in stratocumulomutatus.

Mist Mist: Set of microscopic water droplets, suspended in the atmosphere. It does not reduce visibility like fog and is often mistaken for drizzle.

Mist:  set of microscopic droplets of water suspended in the atmosphere. It does not reduce visibility like fog and is often confused with drizzle. 
Mist:  suspension of water droplets in the atmospheric layer juxtaposed to the surface of the Earth, reducing the horizontal visibility to not less than 1km. It is also referred to as mist.

Mist:  suspension of fine dust particles and / or smoke in the air. Invisible to the naked eye, the particles reduce visibility and are numerous enough to give the air an opaque appearance.  


National Hurricane Center: Tropical Prediction Center, is the National Weather Service sector responsible for the tracking and forecasting of tropical cyclones in the North Atlantic, Caribbean, Gulf of Mexico and the Eastern Pacific. For more information, contact the NHC in Miami, Florida.

National Oceanic and Atmospheric Administration (NOAA ): United States Department of Commerce Section, is the home organization of the National Weather Service. Promotes environmental management at a global level with an emphasis on atmospheric and marine resources. For additional information, contact NOAA, located in Silver Spring, Maryland.

Nimbustratus: Cloud typical of the formation of rain or snow. Often, the high precipitation intensity generated does not allow observing the base of these clouds. Generally associated with the autumn and winter climatic conditions, these clouds can, however, occur in any season.

Normal Nivometer: The  recognized standard value of a meteorological element, considering the average of its occurrence in a given location, for a determined number of years. "Normal" means the distribution of the data within a standard incidence range. Parameters may include high, low temperatures and variations; pressure, precipitation as rain, snow, etc .; winds, speed and direction; cloudiness, relative humidity, etc. 

Noctilucent:  very rare cloud that forms above the level where the pearly clouds are. They only appear at night in the ionosphere and can only be seen because of its phosphorescent characteristic. 

Node: Measure of nautical speed, equal to the speed in which a nautical mile is traversed in an hour. Used mainly for maritime interests and in weather observations. A node is equivalent to 1,852 kilometers per hour or 1,151 miles per hour.

Normal: Value recognized as default for a weather parameter. It considers the average of its occurrence, in a certain place, for a definite period of years. "Normal" is associated with the distribution of values ​​within a standard incidence range. The parameters considered can include temperatures (maximum, minimum and variations), pressure, relative humidity, precipitation (rain, snow, etc.), winds (speed and direction), occurrence of storms, cloud cover, among others.

Note: In meteorology, it is the estimate of one or more meteorological parameters, such as temperature, pressure and / or wind, describing the state of the atmosphere near the surface or at altitude. An observer is one who records the measured values ​​and describes the meteorological parameters.

Numerical Model: computer model containing atmospheric equations in order to obtain the weather forecast for several days. 


Observed Meteorology: a  chart that provides information on the significant weather conditions that are being monitored by meteorologists and / or the news about disturbances caused by adverse weather conditions.

Occlusal front: Also known as "occlusion," it is a complex system that forms when a cold front reaches a warm front. It develops when three masses of air with different temperatures collide. The occlusion may be hot or cold, depending on the interaction between these air masses.

Openings:  Holes through which the sky is observed when it is almost all covered by clouds. 

Orogenic Survey:  when moist air is forced to rise due to a major obstacle. Cooling can result in cloud formation.  

Overcast:  sky covered by eight-eighths of a cloud layer.

Oxygen: Colorless, odorless and tasteless gas. Oxygen is the second most abundant component of dry air, accounting for 20.946% of its total.

Ozone: Almost colorless gas, with characteristic odor, composed of molecules formed from the union of three oxygen atoms.

Ozone layer: Layer of the atmosphere containing a high proportion of oxygen, in the form of ozone. This layer acts as a filter, protecting the planet from ultraviolet radiation. It lies between the troposphere and the stratosphere, approximately 15 to 20 kilometers (9.5 to 12.5 miles) above the Earth's surface.



Paleoclima:  climate of a prehistoric period whose main characteristics can be reconstituted. 

Pampero:  wind from Argentina and southern Brazil. Wind with a strong gradient, which brings a dry and cold Patagonian air. 

Parallax error:  one of the errors of reading of the meteorological instruments, mainly of the barometer. It is due to the refractive properties of light and optics. 

Parantisselênio:  Photometeoro of the family of the halos analogous to the parantélio, being that the luminous star is the moon. 

Parassenium:  optical phenomenon of the family of halos, similar but less bright than the parell, being that the luminous star is the moon. 

Partly cloudy : The weather conditions in which there are clouds but no full coverage of the sky occurs at any time.

Path:  path followed by a body or portion of the fluid as it moves in space. 

PILOT code:  Indicates the international code of winds at altitude. 

Pluviometer-Udometer:  instrument that measures the rate of rainfall. Its unit of measure are hundredths of inches (0.01). 

Pluviometric Factor:  obtained by squeezing the total amount of precipitation by the average temperature. 

Polar front : Semi-continuous and semi-permanent border between masses of polar air and masses of tropical air. An integral part of a meteorological theory known as "Polar Front Theory".

Polar orbit satellite: Satellite whose orbit includes passages close to, or on both Poles of the Earth.

Potential Temperature: The  temperature that the portion of the air in question would reach if it were adiabatically displaced to a reference pressure level, where the temperature at the pressure level is constant gas, the specific heat of the air, at constant pressure. 

Potential Vorticity: defined as the product of absolute vorticity and static stability

Precipitation of rain and ice : Typical precipitation of the winter, which is manifested by the fall of rain and small stones or ice balls that rebound when they fall on the ground or any other rigid surface. It is reported as "PE" in weather observations and in METAR code.

Precipitation: All forms of water, liquid or solid, that fall from the clouds, reaching the ground. It can be: drizzle, freezing drizzle, freezing rain, hail, ice crystals, small ice balls, rain, snow, small snowballs and snow grains. The amount precipitated is usually represented in millimeters of its liquid state, which falls over a given region, over a given time interval.

Predomination of Sun:  sun for most of the period.

Pressure : It is the force per unit area, exerted by the weight of the atmosphere, on a point located on or above the Earth's surface.

Pressure Altimeter : Aneroid barometer, calibrated to indicate altitude in units of distance.

Pressure at sea level : Atmospheric pressure relative to mean sea level, usually determined from pressure observed in season.

Pressure Gradient Force: force acting on a fluid element due to spatial pressure variation. It acts in the opposite direction of the pressure gradient and its intensity is proportional to the gradient modulus. 

Photometeoros:  luminous phenomenon produced by the reflection, refraction, diffraction or interference of the light coming from the Sun or the Moon. They can be observed in the following conditions: in clean air like mirage, scintillation, green ray; to the surface of the clouds or within them as phenomena of halo, crown, biao, glory; and from hydrometeors or litometeors like rainbow, white rainbow, bishop's ring, crepuscular rays. 

Persistence:  degree of constancy of a meteorological element when a mass of air is subject to modifying factors. 

Peak:  point of intersection of the cold and hot fronts of an extratropical cyclone.

Piezotropy:  condition of the atmosphere when the density of some meteorological element depends solely on the pressure. 

Plot:  representation of the general weather conditions of a given weather station on weather charts by means of symbols and figures. 

Pluviometry: a  study of precipitation including its nature, distribution and measurement techniques. 

Pressure system:  inspanidual character in cyclonic scale of atmospheric circulation, commonly used to indicate both a high and low pressure and less used to indicate a trough or crest. 

Probe radar:  equipment used to determine the winds at altitude by means of radar. 

Psychrometer : An instrument used to measure the content of water vapor, or moisture, in the atmosphere. It consists of two thermometers, one of wet bulb and one of dry bulb. The value of the difference between the temperatures recorded in these two thermometers is used to estimate the air humidity.

Pulsation:  Slight variations in the readings of the barometer that are caused by the gusting winds or by the oscillation of a ship.


There are currently no terms starting with this letter in our glossary.


Radiation : The process by which energy is propagated through any medium in the form of waves. It can be exemplified by electromagnetic radiation, which emits heat and light, or waves of sound.

Radius: Sudden and visible discharge of electricity, produced in response to intensification of potential difference between cloud and soil; between different clouds; within a single cloud or between a cloud and the surrounding air.

Radiosonde:  stations are meteorological stations that measure the physical properties of the atmosphere at altitude. In general, a balloon is used which carries a radiosonde which, through radio signals, transmits the values ​​of atmospheric pressure, temperature and humidity in several levels. 

Rain gauge: An instrument used to measure the amount of rainfall accumulated. In Brazil, the values ​​obtained are usually presented in millimeters.

Rain showers: strong rain originating from cumulunimbos clouds, of unexpected beginning and end.

Rainbow: A luminous arc that displays all the colors of the visible spectrum of light, from red to violet. It is created by refraction, by total reflection and by the dispersion of light. It is visible when the sun's rays traverse a layer of air containing vaporized water or water droplets, which occurs during or immediately after a rain. The rainbow is always seen in the sky on the opposite side of the sun.

Rainfall: Precipitation in the form of liquid water, with droplets larger than 0.5mm. If dispersion is high, this dimension can be reduced. It is reported as "RA" in weather observations and in METAR code. The rain intensity is based on the rate of your fall. "Very Light" results from scattered drops that do not even completely wet a surface. "Light" has drop rate of less than 2.5mm per hour. "Moderate" has drop rate between 2.5mm and 7.5mm per hour. "Strong" has drop rate higher than 7.5mm per hour.

Rainfall quotient: the  ratio of the amount of precipitation collected during a month to an amount that would be obtained if the average annual quantity was equally distributed over all days of the year. 

Rainy:  Cloudy overcast with rain continues throughout the period.

Relative humidity: Ratio between the amount of water vapor contained in air and the maximum amount that air can contain under the same temperature and pressure conditions. It is expressed as a percentage.

Relative Vorticity:  given by rotational relative velocity. In large-scale dynamic meteorology, it is generally interested only in the vertical component of relative vorticity.

Resolution:  precision grid of the model. For example, the ETA model considers relief details and regional conditions for a 40 by 40km grid.

Rotor:  vector function that represents the degree of movement of the vortex around a point. 

Radar: Acronym for Radio Detection And Ranging ("Radio Distance Detection and Measurement"). It is an electronic instrument used to detect objects and estimate their distance. Its principle of operation is based on the phenomena of scattering and reflection, resulting from the interaction between these objects and radio waves. Clouds and precipitation are detected by Radar equipment, depending on the intensity of the electromagnetic signals reflected by them.

Return  Discharge: intense discharge and very luminous that follows, immediately, to the initial electrical discharge in the reverse direction, in the same channel of a lightning. 

Recurvature:  change in the trajectory of a tropical cyclone from its normal initial movement to the west, in its normal posterior movement to and from the pole. 

Rocket Lightning:  flash of lightning that gives the appearance of a rapid progression perceptible to the eyes both the main trajectory and its branching. 

Rooster-cock:  name given to cirrus clouds in long thin stripes. 

Rossby wave:  is the wave motion in the horizontal plane of the synoptic scale, in which the regions of cyclonic and anticyclonic vorticity alternate as the wave propagates. The restorative force of this wave is the Coriolis force. 

Rotation Movement:  movement responsible for the days and nights. The Earth rotates from west to east around its imaginary axis, which passes through the north and south poles, with a period of approximately 24 hours. 


Saffir-Simpson:  the intensity measure of a hurricane in a rating from 1 to 5. The potential for damage is based on barometric pressure, wind speed and sea level rise. 

Sand Curtain:  Front of a sand or dust storm having the appearance of a gigantic high curtain that moves more or less rapidly. 

Sandstorm:  Sand raised in the air by strong winds. 

Satellite: Any object that is in the orbit of a celestial body, like a moon, for example. The term, however, is often used to define objects constructed by man and that are in the orbit (geostationary or polar) of the Earth. Some of the information acquired by meteorological satellites, such as GOES9, includes temperature and humidity in the upper layers of the atmosphere, record of the temperature at the top of clouds, the surface of the earth and the oceans. The satellites also track the movement of clouds to determine the speed of high-level winds, track the movement of water vapor, monitor the Sun and solar activity, and relay data from meteorological instruments distributed around the globe.

Satellite Image Animation: it  allows to visualize the existence, the density and the displacement of great masses of clouds in the atmosphere. The international satellites covering South America are geostationary (American GOES-8 and European METEOSAT-5) or polar orbit (American series TIROS-N: NOAA-12 and 14).

Satellite Photos: meteorological satellite photos that reveal important information, such as the flow of water vapor, the movement of climatic fronts, and the development of a tropical system. Sequences of satellite-recorded images help meteorologists work out weather forecasts. Some photos are taken during a period of visible light, daylight. Others are taken with infrared lenses, which reveal the temperature of the clouds and can be used day or night. 

Sunny:  dominance of the sun.

Saturation:  condition that exists in the atmosphere when the partial voltage exerted by the water vapor present is equal to the maximum possible voltage at the same temperature. 

Scud:  name usually given to small clouds that normally appear below the clouds that are precipitating. 

Scattered Clouds: A condition in which three to four octaves fall from the celestial vault, through a layer of clouds. The concept results from the division of the celestial vault in eight eighths, considered in the sum of the area covered by clouds, for a specific layer.

Sea Breeze: it is the breeze or the wind near the surface towards the sea that is developed in the coastal regions in the afternoon. The breeze usually penetrates some kilometers up to 100 km into the continent. The circulation in the vertical plane perpendicular to the coast is closed in a depth of 1 to 2 km. 

Semi-permanent pressure systems: Relatively stable and stationary pressure systems and winds where pressure is predominantly high or low with changing seasons. They are not systems of transitory nature, such as systems of low migratory pressure that result from differences in temperature and density.

Semi-stationary front: Front that is almost stationary, with no or reduced displacement observed since its last position record. Also known as front stationary.

Serene:  light or little thick atmospheric vapor that turns into fine rain. 

Simum:  hot dry wind blowing northward in the deserts of Algeria, Syria, and Arabia. 

Siroco:  hot wind blowing from the Mediterranean from the Sahara desert. The sirocco reaches the north of Africa still warm and dry, but as it crosses the Mediterranean it becomes humid, reaching southern hot and humid Italy. It is usually accompanied by a noticeable decrease in visibility. 

Severe weather : Any destructive weather event, usually associated with localized storms such as thunderstorms, blizzards or tornadoes.

SHIP Code: Code  of the International Synoptic Code for Ships. 

Smoke: Small particles, resulting from combustion and suspended in the air. It can turn into dry fog, when transported over long distances (40 to 160 kilometers, or more), and / or when larger particles settle. The remaining particles spread widely throughout the atmosphere. It is reported as "FU" in weather observations and in METAR code.

Snow: Frozen precipitation, in the form of translucent or white ice crystals, usually in hexagonal form and intricately branched. It is often produced by stratus clouds, and snow blows can occur from cumulus clouds. Usually the crystals are grouped in snowflakes. It is reported as "SN" in weather observations and in METAR code.

Snowfall: Frozen, snow-like precipitation characterized by a sudden start and end. It is reported as "SHSN" in weather observations and in METAR code.

Snowfall: Severe weather conditions characterized by reduced temperatures, winds of 56km / h or more, and large amounts of snow precipitating or being blown by the wind. This condition often reduces visibility to about 400 meters or less, and persists for at least three hours. A violent snowstorm is characterized by temperatures around -12 ° C (10 ° F) or lower, winds exceeding 72km / h and visibility reduced to near zero by snowfall.

Solar radiation:  short electromagnetic waves emitted by the Sun responsible for terrestrial heating. 

Sounding:  determination of one or more meteorological elements of the upper atmosphere by means of instruments transported by balloon, aircraft, kite, glider, rocket, etc. 

South Oscillation: Periodic reversal of the atmospheric pressure pattern in the Tropical Pacific Ocean during El Niño events. Represents the distribution of temperature and atmospheric pressure over an oceanic area.

Sparse  rains: intermittent rains during a period in isolated spots.

Specific Volume:  volume of one gas per unit mass. The specific volume of water under normal conditions is 1 liter per kilogram.

Spray:  set of water droplets drawn by the wind to the surface of a vast expanse of water, usually from the crests of the waves and transported at short distances into the atmosphere.

Spring: Season between the spring equinox and the summer solstice. It is characterized by the elevation of the temperature in the middle latitudes. It occurs in the months of September, October and November in the Southern Hemisphere and in the months of March, April and May in the Northern Hemisphere.

Stability:  characteristic of the flow of a fluid that relates to the tendency of decrease or increase of a small perturbation superimposed on it. When the disturbance tends to grow the flow or state of the fluid is said to be unstable. When the disturbance tends to decrease the flow or the state of the fluid is said to be stable. In atmospheric science we find various types of stability or instability depending on the type and scale of disturbance. 

Static Stability:  measurement of the stratification of a planetary fluid. For terrestrial atmosphere, the expression in isobaric coordinates adequately represents the stability conditions for perturbations of vertical air parcels. When it is positive the atmosphere is stable. 

Seasons: each of the four time periods separated by the extremes of the Earth's translation path relative to the Sun, represented by different climatic conditions caused by the inclination of the Earth's axis relative to the plane of the eclectic. The periods are: spring, summer, autumn and winter. 

Stable  time: good weather; Clear or partly cloudy.

Standard Atmosphere: Term defined by the International Civil Aviation Organization (ICAO). It is defined as mean sea-level temperature equivalent to 15 ° C, surface pressure of 1,013,25 millibars, or 760 millimeters of mercury and a temperature reduction of 0,65 ° C, every 100 meters, up to 11 kilometers altitude.

Standard surface pressure: Measurement of an atmosphere of pressure under conditions considered standard. It is equivalent to 1,013.25 millibars; 760 mm of mercury; 29.92 inches of mercury; 1,033 grams per square centimeter or 14.7 pounds per square inch.

Station pressure: Atmospheric pressure relative to station elevation.

Stationary front: Front that is almost stationary, with no or small displacement observed since its last position record. Also known as semi-stationary front.

Storm: Produced by cumulonimbus clouds, these are micro-scale and short-lived events characterized by thunderstorms, lightning, wind gusts, turbulence, hail, ice, rain, downwinds and extreme, tornadoes.

Storm Eye: Center of a tropical storm or hurricane, characterized by a more or less circular area that presents winds with reduced speed and absence of rains. A storm eye will normally develop when the maximum speed of continuous winds exceeds 124km / h. The storm eye can range in size from 8 to 96 kilometers, its average size being about 32 kilometers. In general, there is a reduction in the size of the eye when the storm becomes more intense.

Storm Front:  Vertical accumulation of cold air on a cold front often taking the form of a suspended tongue. 

Storm line:  wind gusts that take place along a line separating areas that present great difference of atmospheric pressure. 

Storm:  Sudden short-lived storm quite akin to a thunderstorm, but not necessarily accompanied by thunder. Longer than a gust. 

Storm: Sudden windstorm, usually accompanied by heavy rain or snow. 

Stratocumulus: A stratus cloud of low height, composed of layers or elements of cloud. It may form from cumulus-type cloud layering and often appears as equally distributed elements, with rounded and / or cylindrical shapes, with the top and base relatively flat. It can assume shades of light gray to dark, depending on the size of the water droplets and the amount of sunlight that passes through it.

Stratus: One of the three basic forms of cloud (the others are cirrus and cumulus). It is also one of two types of low cloud. Stratus is a sheet-shaped cloud, which does not exhibit individual elements, and is perhaps the most common of all low clouds. It is thick and gray and can be observed in uniform layers, located in low heights, rarely occurring above 1,500 meters above the surface. Stratus clouds can give the sky a hazy appearance. Fog can form from stratus clouds that touch the ground. Although it can produce drizzle or snow, it rarely produces intense precipitation. Clouds that produce intense precipitation can occur on the stratus cloud layer.

Subpolar:  low pressure range between latitudes of 50 and 70 degrees north and south. 

Subcooling: A  condition in which the water vapor present in a stable air layer is cooled to or below the freezing point without condensation. 

Street of Clouds: clouds arranged in rows, substantially parallel to the direction of the wind, and seeming to converge, due to the effect of perspective, to one or two opposing points on the horizon.

Subsidence: Descending air movement, usually observed in anticyclones. More frequent when air in upper layers is colder and denser than air at lower levels. The term is generally used to indicate the opposite of atmospheric convection.

Subtropical jet: Marked by a concentration of isotherms and vertical shear. This jet of wind is the boundary between subtropical air and tropical air. It occurs in the Northern and Southern Hemispheres, between approximately 25 and 35 degrees of latitude and, generally, over 12,000 meters in height. It tends to migrate south in the Southern Hemisphere summer and north in the winter.

Subtropical:  range between latitudes of 20 and 50 degrees north and south. 

Synop:  data from surface stations collected at the synoptic times, coded and distributed to the spanersos meteorological organs.

Swell:  wave formed away from the surf, usually associated with synoptic systems like a low pressure, with strong winds and that generate waves with enough energy to "leave" the zone of the generation (proximal of the low). It is also known as marulho.

Summer: Season between the summer solstice and the autumnal equinox. It is characterized as the hottest period of the year except in some tropical regions. It occurs in the months of December, January and February in the Southern Hemisphere and in the months of June, July and August in the Northern Hemisphere.

Sunrise: Daily appearance of the Sun on the eastern horizon, which occurs due to Earth's rotational motion.

Sunset or Sunset: Daily disappearance of the Sun on the western horizon, which occurs due to the Earth's rotating movement.

Sunset:  Daily disappearance of the Sun on the west of the horizon due to Earth's rotational movement. In the United States, it is considered as that moment when the upper extremity of the Sun disappears into the horizon at sea level. In England, it refers to the moment when the center of the sun's disk disappears. The sunset is made according to the average level of sea water. 

Surface layer: it  is the atmospheric layer close to the surface, generally inferior to 100m in which the vertical turbulent transport of the amount of movement is constant.

SYNOP code: Code of international synoptic code for terrestrial meteorological stations. 

Synoptic Chart: Any map or graphic that describes the weather or atmospheric conditions, for a large area, at any given time.

Synoptic Code:  Meteorological code approved by WMO, in which the meteorological elements observed on the surface of the Earth are coded and groups of five figures and transmitted for synoptic purposes. 

Synoptic Map:  any map or chart describing the weather or atmospheric conditions of a large area at any given time. 

Synoptic Scale: Associated with the extension of high or low pressure migratory systems at low levels in the troposphere. It involves the horizontal covering of an area equivalent to or greater than several hundred kilometers.


TEMP Code:  Indicative code of soundings with radiosonde. 

Temperature: Measurement of the level of molecular agitation or degree of heat of a substance, being associated with the substance's ability to receive or transmit heat. It is measured on an arbitrary scale with zero absolute origin, when the molecules theoretically stop moving.

Temperature of air:  temperature reigning in a point of the atmosphere.

Temperature Celsius Scale : Temperature range at which water at sea level has freezing point at 0 ° C and boiling point at 100 ° C. Most commonly used in areas that adopt metric measurement system. It was created by Anders Celsius in 1742. In 1948, the 9th General Conference of Weights and Measures replaced the expression "centigrade degree" with "Celsius degree".

Temperature inversion:  condition by which the air near the surface of the Earth becomes colder than above, that is, the inverse of the normal; the temperature increases with altitude by a short distance. 

Temperature Scale:  means used to measure temperature. There are several temperature scales: Celsius, Fahrenheit, Kelvin, etc. The Celsius scale is based on the freezing point and boiling water, while the Kelvin scale is based on molecular kinetic theory and is the scale used for scientific calculations. 

Terral:  wind that blows from Earth, terrestrial breeze. 

Terrestrial Breeze: it  is the breeze or wind near the surface towards the continent towards the sea that develops in the coastal regions in the nocturnal periods. The breeze affects some kilometers up to 100 km into the sea. The circulation in the vertical plane perpendicular to the coast is closed in a depth of 1 to 2 km. The images are renewed every hour, automatically and the synoptic description of 2 to 3 times a day by the on-call meteorologist. These images support the user in identifying the local meteorological systems in a first assessment of the situation. High resolution images are a great tool during the day because they are visible channel images.

Terrestrial Globe: It  has a geoid shape, with an average radius of 6,371 km, the equatorial radius being about 21.5 km longer than the polar radius. It has a rocky surface layer, called lithosphere, forming the earth's crust. On this layer the hydrosphere, constituted of the oceanic and continental waters, and the atmosphere with its different layers are deposited. 

Thermal Amplitude:  difference between the average of the maximum temperatures and the average of the minimum temperatures.

Thermal Balance:  Balance of gains and losses of heat in a given place and by a given system. 

Thermal Fall:  change in temperature per unit height. 

Thermal sensation: Index describing how temperature is physiologically perceived by humans. When associated with heat, consider the temperature and relative humidity of the air. When associated with cold, consider the effects of wind and temperature. This index does not express the actual air temperature.

Thermal Wind:  geostrophic wind at the base and top of an atmospheric layer. The variation of the geostrophic wind with height is due to the horizontal thermal gradient. 

Thermociclogenesis:  formation of a depression or an anticyclone in the lower part of the troposphere, caused by the theory concerned, by pressure variations in the upper tropopause and in the inner stratosphere and by variations in temperature in the lower layers. 

Thermograph: A thermometer used to measure temperatures and continuously record its values ​​in a graph.

Thermometer: An instrument used to measure temperature. The measured value can be represented by different scales, being Celsius, Fahrenheit and Kelvin the most used in meteorology.

Throat:  Relatively low throat-shaped pressure area between two anticyclones. 

Thunder: Sound emitted by the rapid expansion of gases, along a channel of electric discharge, generated by a ray. More than three quarters of the electric discharge is used to heat gases inside and around the visible lightning area. Temperatures can rise to more than 10,000 degrees Celsius in microseconds, resulting in a violent pressure wave composed of compression and expansion. The rumble of thunder is created when our ears are struck by different waves, resulting from the same discharge, but with origins located at different distances from the observer.

Thunderstorm:  combination of thunder and lightning with or without rain.

Time: State of the atmosphere in a given period, associated with its influence on the life and activities of the human being. It is short-term atmospheric variation, unlike climate changes, which are long-term variations. Weather is often described in terms of luminosity, cloudiness, humidity, precipitation, temperature, visibility and wind.

Time Front:  Place all possible positions of an aircraft after an hour of flight, from the time of departure or from an earlier time front. 

Top:  Well defined surface created by any weather formation covering 4/8 of the sky, above which there is unlimited visibility, horizontal and vertical. 

Tornado: Air column with violent circular movement, extending from the base of a convective cloud to the surface of the Earth. It is the most destructive phenomenon on the scale of atmospheric storms. It can occur anywhere in the world when specific weather conditions occur, although it is more frequent in the United States, in the region known as the Tornado Corridor.

Torvelinho:  diminutive of tornadoes that occur in dry air and with lack of clouds and rain. 

Transmission:  propagation of energy or heat from one place to another. 

Tornado Corridor: Geographical corridor in the United States that extends northward, from Texas to Nebraska and Iowa. In absolute numbers, this is the region of the United States with the highest record of occurrence of tornadoes.

Trade winds: Persistent winds blowing from subtropical high pressure centers to the equatorial trough, or Intertropical Convergence Zone (ITCZ). They are winds of low atmospheric levels characterized by great consistency in their direction. In the Southern Hemisphere the trade winds blow from the southeast and in the Northern Hemisphere blow from the northeast.

Translation Movement:  Earth's trajectory around the sun and determining the duration of the year in 365 days and 6 hours. 

Thermal Efficiency: climatic element in the Thornthwaite climate classification corresponds to the effectiveness of precipitation. 

Tremulina:  Apparent agitation of objects on the surface of the Globe when viewed horizontally. It occurs mainly on Earth when the sun is very bright. It is due to short-term fluctuations in the refractive index of the surface layers of the atmosphere. 

Trend:  international term of use indicative of trend forecasts for aircraft landing. 

Tropical Cyclone : Low-pressure hot-core system that develops over tropical and sometimes subtropical waters. It has organized circulation around its center. Depending on the intensity of the surface winds, the system can be classified as tropical disturbance, tropical depression, tropical storm or hurricane.

Tropical Depression : Tropical cyclone in which the speed of continuous surface winds does not exceed 60km / h (33 knots). It has one or more closed isobars. It may form slowly from a tropical disturbance, or from an east wave with organized development.

Tropical disturbance: Tropical cyclone, in which the continuous surface wind speed does not exceed 60km / h (33 knots). It has one or more closed isobars. It may form slowly from a tropical disturbance, or from an east wave with organized development.

Tropical Disturbance: an area of ​​organized convection that originates in the tropics, occasionally in the subtropics and that maintains its characteristics for 24 hours or more. Often, it is the first phase of development of any subsequent tropical depression, tropical storm or hurricane. 

Tropical Storm : Tropical cyclone whose continuous surface winds range from 63 kilometers per hour (34 knots) and 116 kilometers per hour (63 knots). When a Tropical Storm is identified the phenomenon receives a name and has its trajectory monitored.

Tropical wave: Another name attributed to an east wave. It is an area of ​​low relative pressure that moves to the west in the current of the trade winds. Generally, it is associated with an extensive area of ​​cloudiness and sparse rainfall, and may occasionally give rise to a tropical cyclone.

Turbulence: Irregular and abrupt movements in the atmosphere, caused by the displacement of small swirls in the air stream. Atmospheric turbulence is caused by random fluctuations in the wind flow. It can be caused by thermal or convective currents, differences in relief, variation in wind speed along a frontal zone, or changes in temperature and pressure.

Turbulence in clear sky: Name given to the turbulence that can occur when the air is perfectly clear, without any cloudiness. It is more common in the vicinity of jet streams, where there is horizontal and vertical wind shear, although it is not limited to these areas. It can also occur in regions near mountains, in areas of low pressure at high levels and in regions of shear in the wind. It can be called TAC.

Twister: A slang, used in the United States, as a reference to Tornado.

Typhoon: The name given to tropical cyclones with continuous wind speeds equal to or greater than 120km / h (65 knots) in the western North Pacific Ocean. Tropical cyclones with the same characteristics are called hurricanes in the eastern North Pacific and North Atlantic Ocean, and cyclones in the Indian Ocean.

Turbidity:  Reducing the transparency of the atmosphere caused by the absorption and dispersion of the radiation by suspended or suspended liquid or solid particles that are not clouds. 


Udder: These  are udrometers used to provide a continuous record of precipitation.

Udometers:  simplest instrument to measure rainfall. The amount of precipitation in the vessel is measured at regular time intervals. 

Ultraviolet Index: ultraviolet radiation (R-UV) is the part of the electromagnetic spectrum relating to wavelengths between 100 and 400 nm. According to the intensity that the R-UV is absorbed by the oxygen and ozone, and also by the photobiological effects it tends to spanidir the UV region in three intervals: It can be said that the sun emits energy at practically all the wavelengths of the electromagnetic spectrum permeated by the spanning absorption lines. 44% of all this emitted energy is concentrated between 400 and 700 nm, called visible energy spectrum. The remainder is spanidido between ultraviolet radiation (less than 400nm) with 7%, infrared (between 700 and 1500nm) with 37% and infrared (greater than 1500nm) with 11%. Less than 1% of the emitted radiation is concentrated above the infrared region, such as microwaves and radio waves, and below the ultraviolet region, such as X-rays and gamma rays. 

Umkehr effect:  anomaly caused by the presence of the ozone layer at altitude, from the relative zenith intensities of certain diffuse ultraviolet rays of solar origin, as soon as the sun is near the horizon. 

Units:  are standard measures of the state variables and movement of fluids, bodies and matter in general. The standard basic units used are meter, kilogram, second and degrees Celsius and Kelvin. 

Updrafts:  up and very fast movement of air columns to altitudes of 180 thousand meters. This phenomenon occurs in a hurricane. 

UTC:  Greenwich mean time. 

Universal Time Coordinate: Convention used to identify the reference time on the planet, defined from Zero time zone. This spindle covers the reference meridian, which passes through Greenwich, England, where this method of world time division was initially used. According to the method, the globe is divided into 24 time zones of 15 degrees arc, or distant an hour apart. East of the Greenwich meridian, the spindles range from one to 12 hours, preceded by the negative sign (-), indicating the number of hours to be subtracted to obtain Greenwich Mean Time (GMT). To the west, the time zones are from one to 12 hours, but are preceded by the positive sign (+), indicating the number of hours to be added to obtain the TMG.

Unstable Weather:  bad weather; favorable conditions for rain.


Valley and Mountain Descending Circulation: Heating of an airflow as a result of its downward displacement along the slope of a hill or mountain. Opposite upward movement.

Vertical Development:  happens with cumuliform type clouds, caused by the action of ascending currents of air. They can reach more than 15,000 meters deep, from the base to the top. 

Vertical Velocity:  vertical component of the movement of a portion of the air. Its intensity is weak compared to the horizontal components of movement. 

Vertical movement: it  is the vertical component of the movement of the air parcel. Its magnitude, in general, is much smaller, by two to three orders of magnitude, than the horizontal movements. 

Vertical Shear:  is the vector difference of wind speed at two points of space spanned by the vertical distance between them, is also called vertical wind shear. 

Virga: Liquid or solid precipitation beam, which evaporates before reaching the surface of the earth. Viewed from a distance, it can be confused with a cloud shaped funnel, or tornado. In general, it is produced by Altocumulus, Altostratus, or Cumulonimbus clouds of high base.

Virtual Temperature:  temperature that the dry air would have to match its density with the density of the portion of the air in question, under equal conditions of pressure. As humid air is lighter than dry air under equal pressure conditions.

Visibility: Measure of the opacity of the atmosphere, or the greater distance that a person with normal vision can see a specific object. The National Weather Service classifies the concept into different categories. Surface visibility is determined from a standard observation point. Predominant visibility represents the visibility conditions at the weather station. Sector visibility is the visibility in a specific direction and that represents at least a 45 degree arc of the horizon line. Tower visibility is the determined visibility from the air traffic control tower of an airport.

Vortex:  circular movement assumed by the fluid, appearing in the form of a funnel. 

Vorticity:  establishes a vector field that gives the microscopic measure of rotation at each point of the fluid. It is a vector field defined as rotational speed.

Venturi effect:  Local pressure drop, local wind increase and bursts in certain regions when the wind blows through a narrow passage of mountains or through a gorge. 


Water Balance:  It is a method used to calculate the water resources of a region. It accounts for precipitation, evaporation and takes into account the storage capacity of water in the soil and in the atmosphere. 

Water cycle: The vertical and horizontal transport of water, in all its states, between earth, atmosphere and seas.

Water thunder:  tornado occurring on water. Storm raises surface water to the atmosphere. A trickle of water usually disappears when you find land.

Meteorological Tropics:  two well defined belts of high barometric pressure, which completely surround the Earth. 

Water vapor range:  dark bands in the solar spectrum caused by the absorption of solar radiation by water vapor in the Earth's atmosphere. 

Wind Chill: in a synoptic letter, a short segment of line that ends in the circle of the station and represents the direction from which the wind blows. 

Wavelength:  is the distance between two consecutive ridges or two consecutive ridges of a wave function or field. 

Water vapor: Water in gaseous form. It is one of the most important components of the atmosphere. Due to its molecular content, air containing water vapor is lighter than dry air. This contributes to moist air tending to rise in the atmosphere.

Weather Information:  meteorological bulletins, analyzes, forecasts and any other elements of weather information.  Sun radiation: solar radiation received by Earth. 

Water Sludge:  set of water droplets pulled by the wind from a very large surface of water, usually from the crests of the waves, and transported at a short distance into the atmosphere. 

Weather Maps:  maps of large regions where the meteorologist records the weather data for each weather station. They can be of various meteorological parameters, such as rain, wind, pressure, temperature and others, which will help the predictor to trace or locate air masses, fronts, etc. Weather maps are also called weather charts or synoptic charts. 

Weather station: where different types of instruments are used to make observations and reports on the weather in various parts of the world. The stations can be classified as follows: Synoptic, Climatological stations, Aeronautical Meteorology, Agricultural Meteorology and Space. 

Wind Direction: angle between the direction of the wind and the direction of the pressure gradient. 

Weather Visibility: distance to which one can see and identify a black object of suitable dimensions against the sky on the horizon. 

Weather Warnings: Weather warnings are made available whenever there is a significant weather condition. There are two stages of warning conditions: State of attention when there is a possibility of a weather event occurring within a forecast period of more than 72 hours; and Severe Weather Warning when the prediction term of the phenomenon is less than 48 hours. The warnings bring in detail information about the intensity of the weather phenomenon, the predictability and the reliability of the forecast.

Williwaw:  name given to the wind in Alaska blowing strong gusts of cold air, mixed with rain and snow, and lasts only a minute or two. It is usually accompanied by a wall of dark clouds and a tempestuous downpour. 

Williy-Willies:  name given in Australia for hurricanes.

Wind Capacity:  Total amount of material particles that can be lifted by a wind of a given speed. 

Wind Chill Index: A calculation of temperature that considers the effects of wind and air temperature on the human body. It describes the average loss of heat in a human body and the way the temperature is felt. It is not the current temperature of the air
Index of Temperature and humidity: it shows how the heat and the humidity make us feel. If we know the temperature and the relative humidity, we can know how uncomfortable we are. 

Wind Direction:  Indicates where the wind blows, and is usually represented by the symbols S (south), N (north), E (east), W (west), and intermediate directions, SE (southeast), NE (northeast) , NW (northwest), SW (southwest).

Wind Gradient: is the curvilinear stationary movement tangential to the parallel isobars with curvature of the portions of the air without friction. The three forces acting on the air parcels, pressure gradient, Coriolis and centripetal, maintains a perfect balance and the plots do not suffer acceleration of the magnitude of the wind gradient. Around low pressure centers the wind gradient is larger than the geostrophic wind and around the high pressure centers the wind gradient is smaller than the geostrophic wind.

Wind gust: Sudden and significant increase, or rapid fluctuations, in wind speed. Maximum winds should reach at least 16 knots (28.8 kilometers per hour) and the variation between these highs and the continuous wind should be at least 10 knots (18.4 kilometers per hour). The duration of the wind gusts is usually less than 20 seconds.

Whirlpool:  more or less developed vortex in the atmosphere constituting a local irregularity of the wind. Every wind near the ground contains whirlwinds, which in some places produce bursts.

Wind shear:  Degree of horizontal or vertical variation of direction and wind speed with respect to distance. It is the vectorial difference of the wind speed at two points of space spanned by the distance between them. 

Wind speed: Quantification of air movement in a unit of time. It can be represented in several ways, the most used being: knots, meters per second and kilometers per hour. The unit most often adopted in the United States is miles per hour.

Winds of the West: Term associated with the patterns of persistent winds, with predominant component of the west. They are the dominant winds in the middle latitudes of both hemispheres. Near the surface of the earth, the winds of the west extend from approximately 35 to 65 degrees of latitude while in high levels, they cover an even more extensive area.

Windswept:  violent wind of short duration, which appears and disappears quickly; occurs between adjacent regions that exhibit large pressure differences. 

Wind profile:  graphical representation of wind speed variation with height or distance function. 

Windward Slope:  part of the slope of a hill or mountain, or even a region facing the wind as a result of a major accident. 

Wind:  action and effect of the winds. 

Winter: Season between the winter solstice and the spring equinox. It is characterized by the colder temperatures of the year, when the sun's rays fall more directly on the opposite hemisphere. It occurs in the months of June, July and August in the Southern Hemisphere and in the months of December, January and February in the Northern Hemisphere.

Wind: Air that flows, usually horizontally, relative to the surface of the Earth. The wind is measured and characterized according to its direction, speed, type (bursts or continuous) and spin in the wind direction. Surface winds are measured by weathervants and anemometers, while winds at high atmospheric levels are detected by pilot balloons, weather probes or aircraft information.

Wind Catabáticos:  are winds that are precipitated by the inclined slopes of the mountains for the valleys. It is the opposite of Anabolic winds. 

Windshield: A  device designed to reduce the force of the wind in a region which it protects and is located towards the wind. 

World Meteorological Organization (WMO): World Meteorological Organization (WMO). Founded by the United Nations in 1951, it has 184 members and coordinates global scientific activity, aiming for greater availability and accuracy of meteorological information, as well as other services to the public, for commercial or private purposes. Its activities range from weather forecasting to pollution research, including activities associated with climate change, studies on the reduction of the ozone layer and forecasting tropical storms. For more information, contact WMO, located in Geneva, Switzerland.


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There are currently  no terms starting with this letter in our glossary.


ZCAS - South Atlantic Convergence Zone: a  region with many clouds associated with heavy or intermittent rain that persists for at least four days and can cause major disturbances such as flooding, landslides and overflow.

Zonda: it  is the name given to the dry and hot wind that occasionally blows from the West on the mountain ranges in the Andes, descending on the side of the wind-protected mountain range. Auroras zone:  region around both magnetic poles within which the aurora is more frequent and active.

Zulu - Coordinates of time : Convention used to identify the reference time on the planet, defined from Zero time zone. This spindle covers the reference meridian, which passes through Greenwich, England, where this method of world time division was initially used. According to the method, the globe is divided into 24 time zones of 15 degrees arc, or distant an hour apart. East of the Greenwich meridian, the spindles range from one to 12 hours, preceded by the negative sign (-), indicating the number of hours to be subtracted to obtain Greenwich Mean Time (GMT). To the west, the time zones are from one to 12 hours, but are preceded by the positive sign (+), indicating the number of hours to be added to obtain the TMG.


The ANACPedia Dictionaries classify some terms in “Aviation Subareas” and contain Aeronautical Meteorology terms. Synonyms and information about “occurrence contexts” can be found. Visit the ANACPedia Dictionaries https://www2.anac.gov.br/anacpedia/ing_por/ing-por.htm


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