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84 Cards in this Set

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air pressure

the pressure produced by the motion, size, and number of gas molecules and exerted on surfaces in contact with the air; can be measured by mercury or aneroid barometer.

mercury barometer

a device that measures air pressure with a column of mercury in a tube that is inserted in a vessel of mercury

aneroid barometer

a device to measure air pressure using a partially emptied, sealed cell


the horizontal movement of air relative to Earth's surface; produced essentially by air pressure differences from place to place; also influenced by the Coriolis force and surface friction. Turbulence adds wind updrafts and downdrafts and a vertical component to this definition


a device to measure wind speed (velocity)

wind vane

a weather instrument used to determine wind direction; winds are named for the direction from which they originate

pressure gradient force

A force that causes air to move from areas of high barometric pressure (more dense air) to areas of lower barometric (less dense air)pressure due to pressure differences, causing winds. Without pressure gradient force, there would be no wind.

Coriolis force

A deflective force, makes wind that travels in a straight path appear to be deflected in relation to Earth's rotating surface. Deflects wind to the right in the Northern Hemisphere and to the left in Southern Hemisphere. Without Coriolis force, winds would move along straight paths between high- and low-pressure areas.

friction force

Drags on the wind as it moves across surfaces; it decreases with height above the surface. Without friction, winds would simply move in paths parallel to isobars and at high rates of speed.


an isoline connecting all points of equal pressure

geostrophic wind

Wind moving between pressure areas along a path parallel to isobars. In the upper troposphere, the pressure gradient force equals Coriolis force, so the amount of deflection is proportional to air movement.


A dynamically or thermally caused area of high atmospheric pressure with descending and diverging air flows that rotate clockwise in the Northern Hemisphere, and counterclockwise in the Southern Hemisphere


A dynamically or thermally caused area of low atmospheric pressure with converging and ascending air flows that rotate counterclockwise in the Northern Hemisphere, and clockwise in the Southern Hemisphere.

equatorial low-pressure through

a thermally cause low-pressure area that almost girdles the Earth, with air converging and ascending all along it extent; also called intertropical convergence zone. Also called intertropical convergence zone

polar high-pressure cell

a weak, anticyclonic, thermally produced pressure system positioned roughly above each pole

subtropical high-pressure cell

a dynamically high-pressure area; found converging roughly the region from 20-35 degrees in both the north and the south latitudes; responsible for the hot, dry areas of Earth's arid semiarid deserts.

subpolar low-pressure cell

A region of low pressure centered approximately 60 degrees latitude in the North Atlantic near Iceland and in the North Pacific near the Aleutians, as well as in the Southern Hemisphere. Air flow is cyclonic; it weakens in summer and strengthens in winter.

trade winds

North east and southeast winds that converge in the equatorial low-pressure through, forming the intertropical convergence zone.


The predominant wind-flow pattern from the subtropics to the hi latitudes in both hemispheres

polar front

A significant zone of contrast between cold and warm air masses; roughly situated between 50-60 degrees North and South latitude

polar easterlies

A variable, weak, cold, and dry wind moving away from the polar region; an anticyclone circulation

Antarctic high

A consistent high-pressure region centered over Antarctica; source region for an intense polar air mass that is dry and associated with the lowest temperatures on earth

constant isobaric surface

And elevated surface in the atmosphere on which all points have the same pressure, usually 500mb. Along this constant-pressure surface, isobars mark the paths of upper air winds

Rossby wave

An undulating motion in the upper air westerly circulation at middle and high latitudes

jet stream

The most prominent movement in upper level westerly wind flows; irregular, concentrated, sinuous bands of geostrophic wind, traveling at 300 km/h (190mph)

land and sea breezes

The wind along coastlines an adjoining interior areas created by different heating characteristics of land and water surfaces; onshore (landward) breeze in the afternoon and offshore (seaward) breeze at night

Mountain and valley breezes

A light wind produced as cooler mountain air flows downslope at night and as warmer Valley air flows upslope during the day

katabatic winds

Air drainage from elevated regions, flowing as a gravity wind. Layers of air at the surface cool, become denser, and flow downslope; known worldwide by any names


From the Arabic word mausim, meaning "season"; refers to the annual cycle of dryness and wetness, with seasonally shifting winds produced by changing atmospheric pressure systems; affects India, Southeast Asia, Indonesia, northern Australia, and portions of Africa

western intensification

The piling up of ocean water along the western margin of each basin, to height of about 15 cm (6in); produced by the trade winds that drive the oceans westward in a concentrated channel

upwelling current

Ocean currents cause surface waters to be swept away from the coast by surface divergence or offshore winds. Cool, deep waters, which are generally nutrient rich, rise to replace the vacating water.

downwelling current

An area of the sea where a convergence or accumulation of water thrusts excess water downward, occurring, for example, at the western end of the equatorial current or along the margins of Antarctica

thermohaline circulation

Differences in temperature and salinity produced density differences important to the flow of deep, sometimes vertical, currents. Traveling at slower speeds than wind-driven surfaces currents, the thermohaline circulation hauls larger volumes of water.

phase change

The change in phase, or state, among ice, water, and water vapor; involves the absorption or release of latent heat


A process in which ice evaporates directly to water vapor or water vapor freezes to ice

latent heat

The heat energy that is absorbed or released in the phase change of water and is stored in one of the three states; ice, water, or vapor; includes The latent heat of melting, freezing, vaporization, evaporation, and condensation.

latent heat vaporization

The heat energy that is absorbed from the environment in a phase change from liquid to water vapor at the boiling point; under normal sea-level pressure, 540 cal must be added to each gram of boiling water to achieve a phase change to water vapor.

latent heat condensation

The heat energy that is released in a phase change from water vapor to a liquid; 585 cal are released from 1 g of water vapor that condenses at 20 degrees C (68°F)

latent heat evaporation

The heat energy that is required to change phase from liquid to water vapor; under normal sea level pressure, 585 cal must be added to 1 g of water at (20 degrees C or 60 degrees F) to achieve a phase change to water vapor


The water vapor content of the air. The capacity of the air to absorb water vapor is mostly a function of the water vapor temperature and air temperature.

relative humidity

The ratio of water vapor actually in the air (content) compared to the maximum water vapor possible (capacity) at that temperature ( expressed as a percentage.


The condition of air that is holding all the water vapor that it can hold at a given temperature

dew-point temperature

The temperature at which a given mass of air becomes saturated, absorbing all the water it can. Any further cooling or addition of water vapor results in active condensation.

vapor pressure

That portion of total air pressure that results from water vapor molecules; expressed in millibars(mb). At a given temperature, the maximum capacity of the air is termed it saturation vapor pressure.

specific humidity

The mass of water vapor (in grams) per-unit mass of air (in kilograms) at any specific temperature. The maximum mass of water vapor that a kilogram of air can hold any specific temperature is termed the maximum specific humidity.


The condition of a parcel (a body of air with a specific temperature and humidity, perhaps 300 m, 1000 feet, in diameter), weather remains where it is or changes its initial position. The parcel is stable if it resists displacement upward; it is unstable if it continues to rise.

normal lapse rate

The average rate of temperature decrease with increasing altitude in the lower atmosphere; an average value of 6.4 degrees C per km, or 1000 m (3.4 degrees F per 1000 ft).

environmental lapse rate

The actual lapse rate in the lower atmosphere at any particular time under local weather conditions; May deviate above or below the average normal lapse rate of 6.4 degrees C per 1000 m.


Pertaining to the heating and cooling of a descending or ascending parcel of air through compression and expansion, without any exchange of heat between the parcel and the surrounding environment.

dry adiabatic rate

The rate at which a parcel of air that is less then saturated cools (if ascending) or heats (if descending); a rate of 10 degrees C per 1000 m (5.5 degrees F per 1000 ft)

moist adiabatic rate

The rate at which a parcel of saturated air cools in ascent; rat of 6 degrees C per 1000 m (3.3 degrees F per 1000ft)


An aggradation of moisture droplets and ice crystals that are suspended in air and are great enough in volume and density to be visible; Basic forms include stratiform, cumuliform, and cirroform

moisture droplet

The initial composition of clouds; each droplet measures approximately 0.002 cm (0.0008 inches) in diameter and is invisible to the human eye

condensation nuclei

Necessary microscopic particles on which water vapor condenses to form moisture droplets; can be sea salts, dust, soot, or ash


A stratiform (flat, horizontal) cloud generally below 2000 m (6500 feet)


A rain-producing, dark, grayish stratiform cloud characterized by gentle drizzles


A bright puffy cumuliform cloud up to 2000 m (6500 feet) in altitude


A lumpy, grayish, low-level cloud, patchy with sky visible; sometimes present at the end of the day.


Mid-level, puffy clouds that occur in several forms; patchy rows, wave patterns, a "mackerel sky", or lens-shaped "lenticular" clouds.


Wispy filaments of ice crystal clouds that occur above 6000 m (20,000 feet); they appear in a variety of forms, from feathery hairlike fibers to veils of fused sheets.


A towering, precipitation producing cumulus cloud that is vertically developed across altitudes associated with other clouds; frequently associated with lightning and thunder and thus sometimes termed a thunderhead.


A cloud, generally stratiform, in contact with the ground, with visibility usually restricted to less than 1 km (3300 feet).

advection fog

The active condensation formed when warm, moist air moves laterally over cooler water and land surfaces, causing the lower layers of the overlying air to be chilled to the dewpoint temperature.

evaporation fog

A fog formed when cold air flows over the warm surface of a lake, ocean, or other body of water as the water molecules evaporate from water surface into the cold, overlaying air; also known as a steam fog or sea smoke

upslope fog

The fog that forms when moist air is forced to higher elevations along a hill or mountain and is thus cold

valley fog

The settling of cooler, more dense air in low-lying areas, which produces saturated conditions and fog

radiation fog

A fog formed by a radiative cooling of the surface, especially on clear nights in areas of moist ground; occurs when the air layer directly above the surface is chilled to the dewpoint temperature, thereby producing saturated conditions.

air mass

A distinctive, homogeneous body of air in terms of temperature and humidity that takes on the moisture and temperature characteristics of its source region

convergent lifting

Air flows in conflict force lifting and displacement of air upward, initiating adiabatic process.

convectional lifting

Air passing over warm surfaces gains buoyancy and lifts, initiating adiabatic processes

orographic lifting

The uplift of migration air masses in response to the physical presence of a mountain, a topographic barrier. The lifted air cools adiabatically as it moves upslope and may form clouds and produce increased precipitation.

rain shadow

The area on the leeward slopes of a mountain range, in the shadow of the mountains, where precipitation receipt is greatly reduced compared to that of windward slopes.

cold front

The leading edge of a cold air mass; identified on a weather map as a line marked with a series of triangular spikes pointing in the direction of frontal movement

warm front

The leading edge of an advancing warm air mass that is unable push cooler, passive air out of the way; tends to push the cooler, underlying air into a wedge shape; noted on weather maps with a series of rounded knobs placed along the front in the direction of the frontal movement

squall line

A zone slightly ahead of a fast-advancing cold front, where wind patterns are rapidly changing and blustery and precipitation is strong


A flash of light caused by tens of millions of volts of electrical charge igniting the air to temperatures of 15,000-30,000 degrees C


The violent expansion of suddenly heated air, created by lightning discharges, sending out shockwaves as an audible sonic bang.


A type of precipitation formed when a raindrop is repeatedly circulated above and below the freezing level in a cloud, with each cycle adding more ice to the hailstone until it becomes to heavy to stay loft


A strong linear wind in excess of 26 m/s (58 mph) associated with thunderstorms and bands of shower crossing a region


A large, rotating circulation initiated within a parent cumulonimbus cloud at the mid-troposphere level; generally produces heavy rain, large hail, blustery winds, and lightning; may lead to tornado activity

funnel cloud

The visible swirl extending from the bottom side of a cloud, which may or may not develop a tornado. A tornado is a funnel cloud that has extended all the way to the ground.


An intense, destructive cyclonic rotation, developed in response to extremely low pressure; associated with mesocyclone.


An elongated, funnel shaped circulation formed when a tornado takes place over water

tropical cyclone/ hurricane/ typhoon

A cyclonic circulation originating in the tropics, with winds between 30-64 knots (39-73 mph; 63-118 km/h); characterized by closed isobars, circular organization, and heavy rains.