Meteorology Topics

Absolute Altitude
Altitude above the actual surface, either land or water, of a planet or natural satellite.
Absolute Humidity
The total mass of water vapour present in the air per unit volume, generally given in g/m3.
Absolute Temperature
Temperature measured on a scale that sets absolute zero as zero.
Adiabatic Saturation Process
A process to determine absolute or relative humidity.
Advection
The transfer of matter such as water vapour or heat through the atmosphere as a result of horizontal movement of an air mass.
Aerology
The study of atmospheric conditions away from ground level.
Aerometry
The science of measuring the air, including the doctrine of its pressure, elasticity, rarefaction, and condensation.
Aeronomy
The study of the upper regions of the atmosphere where ionization, dissociation, and chemical reactions take place.
Aeropause
A region of indeterminate limits in the upper atmosphere, considered as a boundary or transition region between the denser portion of the atmosphere and space.
Air Sounding
Measuring atmospheric phenomena or determining atmospheric conditions at altitude.
Albedo
The ratio of the amount of radiation reflected from an object's surface compared to the amount that strikes it.
Altocumulus
Composed of flattened, thick, gray, globular masses, this middle cloud genus is primarily made of water droplets.
Altocumulus Castellanus
A middle cloud with vertical development that forms from altocumulus clouds.
Altostratus
Middle cloud genus is composed of water droplets, and sometimes ice crystals.
Anemometer
A sensor that measures wind speed.
Anticyclone
A relative pressure maximum. An area of pressure that has diverging winds and a rotation opposite to the earth′s rotation.
Apparent Horizon
Where the shy appears to meet the Earth.
Atmospheric Boundary Layer
The atmospheric layer adjacent to the surface of the Earth that is affected by friction against the surface boundary.
Atmospheric Duct
An almost horizontal layer in the troposphere.
Atmospheric Windows
The spectral bands in which the atmosphere least affects the transmission of radiant energy.
Automated Surface Observing System
This system is a collection of automated weather instruments that collect data.
Automatic Weather Station
A weather station that accurately and automatically measures and records meteorological variables over extended periods.
Backing
A counterclockwise shift in the wind direction in the Northern Hemisphere at a certain location. In the Southern Hemisphere, it is clockwise.
Ball Lightning
A relatively rare form of lightning, consisting of a reddish, luminous ball, of the order of 0.3m in diameter, which may move rapidly along solid objects or remain floating in midair.
Barogram
A continuous trace of air pressure variation with time, typically produced by a barograph.
Barograph
A recording type instrument that provides a continuous trace of air pressure variation with time.
Barometric Pressure
The total pressure exerted by the atmosphere.
Beaufort Scale
In 1805 Admiral Beaufort drew up a scale of wind strengths related to commonly observable phenomena.
Ceiling Light
An instrument consisting of a drum and an optical system that projects a narrow vertical beam of light onto a cloud base.
Ceilometer
An instrument that is used to measure the angular elevation of a projected light on the base of a cloud.
Choroisotherm
A line representing equal temperature in time.
Cirriform
Clouds composed of small particles, mostly ice crystals.
Cirrocumulus
A cirriform cloud with vertical development, appearing as a thin sheet of small white puffs which give it a rippled effect.
Cirrostratus
A cirriform cloud that develops from cirrus spreading out into a thin layer, creating a flat sheetlike appearance.
Cirrus
Cirrus are thin, wispy clouds composed of ice crystals and often appear as veil patches or strands.
Climate Variability
Variations in the mean state and other statistics of the climate on all temporal and spatial scales beyond that of individual weather events.
Cloud Bank
A well-defined cloud mass that can be observed at a distance.
Cloud Cover
The amount of cloud covering the sky, measured in 1/8th.
Cloudburst
A sudden, heavy rainfall of a showery nature.
Clouds
A visible collection of minute particle matter, such as water droplets or ice crystals, in the free air.
Cold Air Funnel
Funnel clouds, usually short-lived, that develop from relatively small showers or thunderstorms when the air aloft is very in cold.
Cold Core Thunderstorms
Thunderstorms formed primarily due to steep lapse rates, especially when very cold air aloft overlies warmer surface air.
Comma Cloud
A feature seen on satellite images with a distinctive comma-shape.
Condensation Nucleus
A particle, either liquid or solid, upon which condensation of vapour begins.
Condensation Shock Wave
A sheet of discontinuity associated with a sudden condensation and fog formation in a field of flow.
Condensation Trail
A cloud like streamer or trail often seen behind aircraft flying in clear, cold, humid air.
Constant Level Balloon
A balloon designed to float at a constant-pressure level.
Constant Pressure Balloon
A balloon designed to float at a constant-pressure level. Also called a Constant Level Balloon.
Contrail
Acronym for CONdensation TRAIL. A cloud-like streamer or trail often seen behind aircraft flying in clear, cold, humid air.
Convection
The heat is transfered from the solid or liquid by the surrounding gas.
Crosswind
Any wind that is blowing perpendicular to a line of travel.
Cumuliform
Clouds composed of water droplets that exhibit vertical development.
Cumulonimbus
A vertically developed cumulus cloud, often capped by an anvil-shaped cirriform cloud.
Cumulonimbus Mammatus
A portion of a cumulonimbus cloud that appears as a pouch or udder on the under surface of the cloud.
Cumulus
One of the three basic cloud forms.
Cumulus Fractus
Cumulus clouds that appear in irregular fragments.
Cumulus Humilis
Cumulus clouds with little or no vertical development characterized by a generally flat appearance.
Cumulus Mediocris
Cumulus clouds characterized by moderate vertical development with upper protuberances not very marked in appearance.
Cup Anemometer
A rotation-type anemometer consists of an array of three, or more, hemispherical cups mounted symmetrically about a vertical rotation axis.
Cyclogenesis
The process that creates a new low pressure system or cyclone, or intensifies a pre-existing one.
Cyclone
An area of closed pressure circulation with rotating and converging winds, the centre of which is a relative pressure minimum.
dBZ
A unit of radar reflectivity used in meteorology. The unit measures the amount of energy returned to a weather radar site as a function of the amount transmitted.
Dew Point
The temperature at which water vapour begins to condense.
Dew Point Depression
The difference between dry bulb and dew point temperatures.
Dew Point Hygrometer
An instrument used for determining the dewpoint.
Diffuse Insolation
Sunlight received indirectly as a result of scattering due to clouds, fog, haze, dust, or other obstructions in the atmosphere. Opposite of direct insolation.
Direct Insolation
Sunlight falling directly upon a collector. Opposite of diffuse insolation.
Diurnal Temperature Range
The difference between the maximum and minimum temperature during a day.
Dropsonde
A modified radiosonde package that is dropped by parachute from an aircraft to obtain temperature, pressure, and humidity profiles of the atmosphere below flight level.
Drought Severity Category
A measure of drought severity with categories denoted D0-D5 and higher numbers indicating a more severe drought.
Dry Bulb Thermometer
A thermometer used to measure the ambient temperature.
Environmental Lapse Rate
The rate at which the air temperature decreases as you move higher in the atmosphere.
Flanking Line
A line of attached cumulus or towering cumulus clouds of descending height.
Fractus
The elements of cumulus and stratus clouds that appear in irregular fragments.
Free Atmosphere
The layer of the atmosphere above the boundary layer that is not affected by surface friction.
Fujita-Pearson Scale
An empirical scale for estimating the wind speed of a tornado from the damage it causes.
General Circulation
The large scale motions of the atmosphere and the ocean as a consequence of differential heating on a rotating Earth, aiming to restore the energy balance of the system through transport of heat and momentum.
Global Surface Temperature
The area-weighted global average.
Global Warming
The prediction that climate will warm as a result of the addition to the atmosphere of humanly produced greenhouse gases.
Globe Lightning
Another name for Ball Lightning.
Greenhouse Gases
The three most powerful long lived greenhouse gases in the atmosphere are: Carbon Dioxide (CO2), Methane (CH4) and Nitrous Oxide (N2O).
Hair Hygrometer
Measures atmospheric relative humidity by means of the variation in length of a bundle of human hairs as they adsorb atmospheric water vapour.
Heat Island Effect
A dome of elevated temperatures over an urban area caused by structural and pavement heat fluxes, and pollutant emissions.
Horizontal Range
The maximum distance in the horizontal direction that one can see.
Hot-Wire Anemometer
Uses the wind induced changes in the temperature of a metal wire that is heated by an electric current and cooled by convective heat loss.
Humidex
Abbreviation of Humidity Index.
Humidity Index
A number which combines the air temperature in Celsius and the amount of humidity in order to give a single number to represent the perceived discomfort of weather that is hot and humid.
Hydrologic Cycle
The cycle of water from evaporation through condensation to precipitation.
Hygrometer
A tool for measuring the humidity of the air.
Hypobaric
Pertaining to low atmospheric pressure.
Icing
Condition arising when atmospheric moisture freezes on the external surfaces of an aircraft.
Insolation
The total amount of solar radiation energy received on a given surface area during a given time.
Ionospheric Storms
Disturbances in the earth′s magnetic field that make communications practical only at lower frequencies.
Lenticular Cloud
A cloud species which has elements resembling smooth lenses or almonds and more or less isolated.
Lightning
An atmospheric discharge of electricity usually accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms.
Linke Turbidity Factor
A measure of atmospheric turbidity, equal to the ratio of total optical depth to the Rayleigh optical depth.
Mackerel Sky
The name given to cirrocumulus clouds with small vertical extent and composed of ice crystals.
Mammatocumulus
An obsolete term for cumulonimbus mammatus, it is a portion of a cumulonimbus cloud that appears as a pouch or udder on the under surface of the cloud.
Mare Tail
The name given to thin, wispy cirrus clouds composed of ice crystals that appear as veil patches or strands, often resembling a horse′s tail.
Meridional Flow
Atmospheric circulation in which the north and south, or meridional, component of motion is unusually pronounced.
Mesopause
Extremely cold region of the earth′s atmosphere at an altitude of approximately 80 km, representing the boundary between the mesosphere and the overlying thermosphere.
Meteorograph
A collection of automatic meteorological recording instruments, often times describing the package that is carried aloft on an instrument platform.
Meteorological
Of or pertaining to atmospheric phenomena, especially weather and weather conditions.
Micrometeorology
The detailed study of the weather at a specific location.
Minimum Thermometer
A thermometer designed to automatically register the lowest temperature attained during any time interval before it is set.
Natural Convection
Movement of a fluid caused only by temperature differences.
Nimbostratus
This cloud exhibits a combination of rain or snow, and sometimes the base of the cloud cannot be seen because of the heaviness of precipitation.
Noctilucent Clouds
Rarely seen clouds of tiny ice particles that form approximately 75 to 90 kilometers above the earth′s surface.
North Atlantic Oscillation
Consists of opposing variations of barometric pressure near Iceland and near the Azores.
Ocean Conveyor Belt
The theoretical route by which water circulates around the entire global ocean, driven by wind and the thermohaline circulation.
okta
Unit of proportion equal to 1/8, used in meteorology to record the fraction of the sky covered by clouds.
Overcast
The amount of sky cover for a cloud layer that is 8/8ths, based on the summation layer amount for that layer.
Ozone Layer
An atmospheric layer that contains a high proportion of ozone and acts as a filtering mechanism against incoming ultraviolet radiation.
Pentad
A period of 5 days.
Pilot Balloon
A balloon that ascends through the atmosphere at a constant rate and is tracked by a theodolite in order to obtain timed data for the computation of the wind speed and wind direction at various levels in the upper air above the station.
Pressure Gradient
The change in pressure per unit of distance.
Psychrometric Chart
A chart that shows relationship between the temperature, pressure and moisture content of the air.
Psychrometry
The study of air-vapour mixtures.
Radiosonde
A small, expendable, balloon-borne instrument package with a radio transmitter used to measure the air temperature, pressure and humidity of the atmosphere above the earth′s surface.
Rain Bucket
Device for measuring rain fall.
Rain Gauge
Instrument used to measure the total amount of precipitation that falls upon a given unit area during a specified time interval.
Rocket Sounding
A probe of the upper atmosphere with a meteorological rocket to produce a record of the vertical variation of a weather element such as air temperature, density, composition or winds.
Rocketsonde
An instrument package carried aloft by a meteorological rocket to make a measure one or more weather elements in a sounding of the upper atmosphere.
Rockoon
A high-altitude sounding system consisting of a small solid-propellant research rocket carried aloft and launched by a large balloon.
Roll Cloud
A relatively rare, low-level, horizontal, tube-shaped cloud.
Rotor Cloud
An altocumulus cloud formation that can be found in the lee of a mountain or similar barrier.
Sferics Observation
An evaluation, from one or more sferics receivers, of the location of weather conditions with which lightning is associated.
Sferics Receiver
An instrument which measures, electronically, the direction of arrival, intensity, and rate of occurrence of atmospherics.
Sky Cover
The amount of the celestial dome that is hidden by clouds or obscurations.
Solar Constant
The bolometric flux at a distance of 1 AU from the sun = 1.368x103Wm-2
Solar Energy
Electromagnetic energy transmitted from the sun.
Sounding
Any probe of the environment made to obtain information at various levels.
Sounding Rocket
A rocket that carries aloft equipment for making observations of or from the upper atmosphere.
Sporadic E Layer
Irregular, cloud-like patches of unusually high ionization.
Stratiform
Clouds composed of water droplets that exhibit no or have very little vertical development.
Stratocumulus
A low cloud composed of layers or patches of cloud elements.
Stratosphere
Located between the troposphere and the ionosphere.
Stratus
One of the three basic cloud forms.
Stratus Fractus
Stratus clouds that appear in irregular fragments.
Summation Layer Amount
The amount of sky cover for each layer is given in eighths of sky cover attributable to clouds or obscurations.
Temperature
A measure as to whether two bodies are hot or cold relative to one another.
Temperature Humidity Index
Actual temperature and humidity of air sample compared to air at standard conditions.
Temperature Inversion
The condition in which warm air is formed above a layer of cool air that is near the earth′s surface.
Thermogram
A continuous trace of temperature variation with time, typically produced by a thermograph.
Thermohygrograph
An instrument for measuring humidity and temperature.
Thermometer
An instrument for measuring temperature.
Thermosphere
The region of the Earth′s atmosphere above the mesopause, starting at 80 km altitude, where the air temperature increases with altitude.
Towering Cumulus
Another name for cumulus congestus.
Tropopause
The cold region in t earth′s atmosphere located about 10 km above the surface.
Troposphere
The portion of the atmosphere, closest to the surface of the earth, where all weather phenomena take place.
True Altitude
Actual height above sea level; calibrated altitude corrected for air temperature.
Umkehr Effect
An anomaly of the relative zenith intensities of scattered sunlight at certain wavelengths in the ultraviolet as the sun approaches the horizon, due to the presence of the ozone layer.
Undercast
An opaque cloud layer viewed from an observation point above the layer.
Upwind
The direction from which the wind is blowing. Also the windward side of an object.
Vapour Trail
A cloud like streamer or trail often seen behind aircraft flying in clear, cold, humid air.
Veering
A clockwise shift in the wind direction in the Northern Hemisphere at a certain location. In the Southern Hemisphere, it is counterclockwise.
Virga
Streaks or wisps of precipitation, such as water or ice particles, that fall from clouds but evaporate before reaching the ground.
Wall Cloud
An abrupt lowering of a cloud from its parent cloud base, a cumulonimbus or supercell, with no visible precipitation underneath.
Water Cycle
Also known as the Hydrologic Cycle.
Wet Bulb Thermometer
A wet wick is placed over a standard thermometer and air is blown across the surface. The temperature depends on how much moisture is in the air.
Whistler
A radiofrequency electromagnetic signal generated by some lightning discharges.
Wind
Air in motion relative to t earth′s surface, caused by the average movement of a large number of molecules of air.
Wind Chill Index
The calculation of temperature that takes into consideration the effects of wind and temperature on the human body.
Wind Shear
The difference between wind velocity measured at two specific locations divided by the distance between those two positions.
Wind Speed
Normally measured relative to the earth′s surface.
Wind Vane
A sensor used to measure wind direction.
Wind Velocity
A vector quantity that describes wind motion in terms of wind speed and wind direction.
Windward
The direction from which the wind is blowing.
Zonal Index
The measure of the strength of the westerly winds of the middle latitudes.
Zonal Wind
Atmospheric wind component which flows along the latitude.

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