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Blowin' in the Wind, Issue #027 Meteorology term glossary - February 1, 2006
February 01, 2006
Hello ,

Need a meteorology term?

Here you find a handy meteorology term lexicon. A glossary of meteorology which gives you a list of common weather terminology and their meanings.

Use control-F to do an individual weather word search on this list.

Acid Rain (or snow) - precipitation with elevated concentrations of chemicals which form acid in the water.

Adiabat - a line on a tephigram or skew-t chart used to show the thermodynamic path of a moving parcel of air, when it does not gain nor lose any heat.

Adiabatic lapse rate - how quickly the temperature of a moving parcel of air changes, even though no heat enters or leaves it.

Dry adiabatic lapse rate - the rate of temperature change for dry (unsaturated) air moving vertically. The temperature will change by 5.4°F per 1000 feet or 9.8°C per kilometre.

Moist adiabatic lapse rate - the rate of temperature change for saturated air.

Environmental lapse rate - the rate of temperature change actually measured in the atmosphere.

Advection - air and its properties, such as temperature, moving across something. Like a lake, or a map.

Air mass - A giant pool of air where properties such as temperature and dewpoint change very little over great distances.

Glossary of air masses

Maritime tropical air mass - warm tropical air in equatorial regions over or near water.

Continental tropical air mass - hot dry air found in places like the Sahara desert.

Maritime polar air mass - cool wet air. Think England.

Continental polar air mass - cold dry air which sometimes produces snow.

Continental arctic air mass - very cold dry air. Siberia.

Air mass thunderstorm - a garden variety storm which causes little if any damage. It occurs a considerable distance from any front.

Air pollutant - anthropogenic or otherwise unusual substance in the air. Usually harmful.

Air quality model - set of equations, such as a computer program, which predicts air quality,

Albedo - how much of incoming radiation, such as light, is reflected off a surface.

Anticyclone - large high pressure area.

Atmospheric Layers

Troposphere - the bottom few miles of the air's depth. Temperature decrease with height at an average rate of almost 6°C per km.

Tropopause - the division between the troposphere and stratosphere temperature suddenly stops decreasing with height at this level.

Stratosphere - a stable layer immediately above the troposphere, temperature slowly increases with height in this layer.

Stratopause - the division between the stratosphere and the mesosphere above.

Mesosphere - a deep layer above the stratosphere temperature decreases with height once again.

Mesopause - the division between the mesosphere and thermosphere, where the temperature is coldest.

Thermosphere - the hottest layer. Very deep layer above the mesopause.

Exosphere - the highest layer in the atmosphere. Very thin with only hydrogen and helium present.

Barometric pressure - the pressure read on your barometer. Atmospheric pressure.

Barometer - an instrument that measures atmospheric pressure

Mercury barometer - uses a vacuum tube filled with mercury to respond to the pressure change, and markings to indicate the value.

Aneroid Barometer - a can that consistently changes shape when the atmospheric pressure changes. A needle attached to it can point to the correct pressure.

Blizzard - High winds and reduced visibilities caused by blowing snow. Low temperatures as well. Exact definitions vary by region.

Boundary layer - the part of the atmosphere closest to the ground.

Chinook - Warm dry foehn, or Föhn wind downwind from the Rocky Mountains.

Climate - multi-year average temperature, precipitation and other weather conditions for a given region.

Cloud classifications -

Altocumulus - Alto (medium altitude, 8000 to 24000 feet or 2400 to 6100 m) + cumulus (piles). Balls or rolls of cloud at medium height.

Altostratus - Alto + stratus (layers). Sheets of uniform gray cloud at medium altitude.

Billow clouds - bands of cloud stretching across the wind field.

Cap cloud - one that sits still over a mountain

Chinook arch - Altostratus clouds downwind of a mountain range. Visible gap between overhead sheet and upwind horizon, when viewed from the ground below.

Cirrocumulus - Cirro (high altitude, over 20000 feet or 6000 m) + cumulus. White patchy clouds with patterns.

Cirrostratus - Thin high sheet clouds.

Cirrus - Wispy white feathers high up in the air.

Cumulonimbus - Cumulus + Nimbus (giving precipitation). Very high piles of cloud, dark and mysterious and lead to thunderstorms.

Cumulus - Piled and puffy pillow clouds, nice day clouds with flat bottoms and cotton-ball tops. White with perhaps a touch of grey.

Fog - A cloud that touches the ground or water surface.

Fractocumulus - Fracto (torn or broken) + cumulus. Puffy clouds with shredded appearance.

Fractostratus - Layered but shredded clouds - also known as stratus fractus.

Lenticular cloud - Smooth lens shape to the cloud and often seen downwind from mountains. For example, alto cumulus standing lenticularis (ACSL).

Nimobstratus - Nimbus + stratus. Boring gray rain clouds.

Rotor cloud - tubes lying downwind along a mountain range.

Stratocumulus - stratus + cumulus. Is it one or the other? Both. Low altitude mounds imbedded in a layer.

Stratus - Grey flannel blanket of cloud.

Towering cumulus - A cumulonimbus in the making. High piled cumulus cloud.

Continental climate - a drier climate with great temperature extremes throughout the year.

Convection - Air moving up and down in a quasi-circular flow, called a cell.

Coriolis force - a mathematical correction to balance forces affecting objects moving on the rotating earth. It looks like an actual force to us and appears to cause moving objects to turn right in the Northern Hemisphere and left in the Southern Hemisphere.

Cyclone - Circular wind pattern around a centre of low pressure. Clockwise in Southern Hemisphere and counter clockwise in the Northern Hemisphere, when viewed from above.

Dewpoint - If air is cooled to the dewpoint temperature without changing its pressure or moisture content, the relative humidity will increase to 100% and fog or dew may form.

Downburst - a strong burst of wind from a thunderstorm, also called a microburst.

Drizzle - liquid water precipitation in the form of tiny droplets, much smaller and slower moving than raindrops.

Eddy - a little whirlpool in moving air or water

El Niño - Spanish for little boy. A change in the Pacific ocean current causing warm water to surface near South America. It usually occurs 2 or 3 times per decade and typically starts around Christmas time, henceforth its name.

Equinox - the exact time the sun is directly above the equator. This happens twice per year, to start both spring and fall.

Freezing rain - rain that freezes after it hits the ground or other object and forms clear ice.

Fronts - baroclinic divisions in the atmosphere. Zones between air masses where temperature changes quite rapidly with horizontal distance.

Cold Front - a front where the colder air is advancing and the warm air is retreating

Warm Front - a front where the warmer air is advancing and the cold air is retreating

Stationary Front - one where nobody seems to be making any progress

Occluded front - a situation where a cold front rams a warm front from behind, as cold fronts are faster.

Trowal - Trough of Warm Air Aloft. An occluded front where cold air is on both sides and the warm air has been completely lifted.

Polar front - divies air polar air masses from tropical air masses.

Arctic front - divides cold air from extremely cold air.

Frozen precipitation

Diamond dust - fine powdery ice crystals that fall in extremely cold weather, even without clouds.

Ice pellets - small hail or sleet type of precipitation.

Graupel - snow pellets - small solid white chunks of snow.

Snow grains - very small solid chunks of snow.

Hail - large, odd-shaped, layered ice chunks that fall from thunderstorms.

Sleet - raindrops that freeze before hitting the earth.

Snow - Large flat ice crystals that hook onto each other and make white flakes.

Gaussian model - a way of calculating concentrations of polluting chemicals from stationary industrial sources. The substance goes downwind and disperses (gets weaker) as it travels, according to Gaussian mathematics.

Geostrophic wind - a theoretical wind which blows along the isobars on a weather map. Pretty good of actual winds high above the ground.

Gradient - The direction to move to experience the greatest change in any weather quantity, such as temperature. Also the rate of that change for a specified distance travelled.

Greenhouse effect - a mechanism trapping heat in the atmosphere, by not allowing radiation to escape from earth too easily.

Haze - a mixture of particles in the air reducing visibility.

Humidity - relative humidity, usually. A way of expressing moisture content in the air.

Humidex - a pseudo temperature that reveals how much the air feels because of high humidity.

Insolation - heat energy that arrives at the surface of the earth.

Inversion - a layer of very stable air. Temperature increases with height.

Subsidence inversion - sinking air compresses and becomes warmer than air below.

Capping inversion - warm air moves overtop of colder air.

Surface temperature inversion - ground cools and then cools air from below, leaving warmer air above.

Isopleth - a curved line on a map joining points where a scalar quantity is equal in value. One side of the curve is higher than its labelled value and the other side is lower.

Isobars - lines of equal atmospheric pressure

Isotachs - lines of equal wind speeds

Isotherms - lines of equal temperature

Isohumes - lines of equal relative humidity

Isodrosotherms - lines of equal dewpoint temperature (or absolute humidity).

Isallobars - lines of equal pressure change over a set period of time.

Isocold - a line you utter when you want to go inside.

Jet stream - fast moving, high elevation stream of wind.

Lake effect storm - small but intense snowstorm downwind of an open lake.

Land breeze - night wind blowing across a beach onto the water. Sea breeze - midday wind blowing across a beach onto the land. Both of these winds blow on the warmer surface.

Latent heat - heat given off by condensation, or absorbed by evaporation, of water.

Lightning - a giant electrical spark jumping between clouds or between a cloud and the ground.

Mesoscale - a study of thunderstorms and similarly sized weather features. These things takes less than a day to pass, usually.

Meteorology - The science that studies the atmosphere.

Microscale - a study of small gusts, eddies and things that last less than an hour, usually. Turbulence, diffusion, and wind shear are examples.

Millibar - an atmospheric pressure of 100 Pascals (Newtons per square metre).

Mixing depth - the maximum height air pollution normally reaches. This varies with geography, season and time of day.

Monsoon - A wind caused by differences in surface temperatures. Some produce heavy rains.

Orography - the interaction of topography with meteorology

Ozone - An oxygen molecule with three atoms stuck together.

Ozone layer - a thin protective layer of ozone gas in the stratosphere.

Polar vortex - cyclonic motion near the pole. Very cold, especially in winter.

Radar - a radio device that calculates the distance to objects, such as storms, within its range.

Radiosonde - the package of weather instruments attached to a weather balloon. Equipped with a radio transmitter.

Rain - water drops greater than 0.5 mm in diameter falling from the sky.

Relative humidity - the ratio of vapour pressure to the vapor pressure that would happen if the air were saturated without changing the temperature.

Rossby waves - the large lobes, about a thousand miles wide, in the waves circulating the earth.

Sling psychromete - a hygrometer for measuring relative humidity. It has two thermometers, one with a wet bulb and one with dry. Can be whirled around to ventilate.

Sloped winds

Katabatic winds - winds that flow downhill, for example Chinook winds (see above), or cool air flowing down at night.

Anabatic winds - winds that flow uphill, usually warm air near midday

Maloja winds - an unusual wind in Switzerland that does the opposite by going uphill at night and downhill during the day.

Solstice - when the sun gets closest to the poles. Marks the beginning of both winter and summer.

Stability - the ability of the atmosphere to suppress vertical motion, convection.

Standard atmosphere - a model of the atmosphere which represents an average for its temperature at various elevations. - THE place to visit. The science of meteorology online.

Subsidence - a large area with decending air. Often free of clouds.

Supercooled - any liquid which remains liquid below its normal freezing point. Synoptic scale - the size of features which take a day or more to pass. They are usually a thousand miles or so across.

Thunder - the sound of a thunderstorm. Caused by rapid air expansion following a lightning bolt.

Trade winds - winds that blow trade ships in a westerly direction.

Vortex - a spiral of wind

Weather - the observable and measure conditions of the outdoor atmosphere.

Wind chill - a pseudo temperature which lets people know what the cooling effect of the wind would feel like.

Wind shear - a velocity gradient. The change in speed and direction over a set change in position of the observer.

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