Air Masses, Weather, Moisture, Clouds, and Precipitation

Flashcards covering key vocabulary terms related to air masses, weather phenomena, moisture in the atmosphere, cloud formation, and precipitation types.

Latent heat

Stored or hidden heat not derived from temperature change, important in atmospheric processes.

Evaporation

Liquid is changed to gas; 600 calories per gram of water are added – called latent heat of vaporization.

Condensation

Water vapor (gas) is changed to a liquid; heat energy is released – called latent heat of condensation.

Melting

Solid is changed to a liquid; 80 calories per gram of water are added – called latent heat of melting.

Freezing

Liquid is changed to a solid; heat is released – called latent heat of fusion.

Sublimation

Solid is changed directly to a gas (e.g., ice cubes shrinking in a freezer); 680 calories per gram of water are added.

Deposition

Water vapor (gas) changed to a solid (e.g., frost in a freezer compartment); heat is released.

Relative humidity

Expressed as a percent; content equals capacity when saturated, resulting in a 100% relative humidity.

Dew point temperature

Temperature to which a parcel of air would need to be cooled to reach saturation.

Dry adiabatic rate

Air expands and cools at 1˚C per 100 meters (5.5˚F per 1000 feet); Descending air is compressed and warms at 1˚C per 100 meters.

Wet adiabatic rate

Commences at condensation level; Heat released by the condensing water reduces the rate of cooling; Rate varies from 0.5˚C to 0.9˚C per 100 meters.

Fog

Cloud with its base at or near the ground; most form because of radiation cooling or movement of air over a cold surface.

Advection fog

Warm, moist air moves over a cool surface.

Radiation fog

Earth's surface cools rapidly, forms during cool, clear, calm nights.

Upslope fog

Humid air moves up a slope; adiabatic cooling occurs.

Steam fog

Cool air moves over warm water and moisture is added to the air; water has a steaming appearance.

Frontal fog/Precipitation fog

Forms during frontal wedging when warm air lifted over colder air; rain evaporates to form fog.

Rain

Droplets have at least a 0.5 mm diameter.

Drizzle

Droplets have less than a 0.5 mm diameter.

Snow

Ice crystals, or aggregates of ice crystals.

Sleet

Wintertime phenomenon; small particles of ice; occurs when warmer air overlies colder air and rain freezes as it falls.

Glaze/Freezing rain

Impact with a solid causes freezing.

Hail

Hard rounded pellets with concentric shells; most diameters range from 1 to 5 cm; occurs in large cumulonimbus clouds.

Rime

Forms on cold surfaces; freezing of super-cooled fog or cloud droplets.

Front

Boundary that separates air masses of different densities where warmer, less dense air is forced aloft and cooler, denser air acts as wedge.

Warm front

Warm air replaces cooler air; Shown on a map by a line with semicircles; Small slope (1:200); Clouds become lower as the front nears; Slow rate of advance; Light-to-moderate precipitation.

Cold front

Cold air replaces warm air; Shown on a map by a line with triangles; Twice as steep (1:100) as warm fronts; Advances faster than a warm front; Associated weather is more violent than a warm front; Intensity of precipitation is greater; Duration of precipitation is shorter.

Stationary front

Flow of air on both sides of the front is almost parallel to the line of the front; Surface position of the front does not move.

Occluded front

Active cold front overtakes a warm front; Cold air wedges the warm air upward; Weather is often complex; Precipitation is associated with warm air being forced aloft.

Cirrus

High, white, thin clouds.

Cumulus

Globular cloud masses often associated with fair weather.

Stratus

Sheets or layers that cover much of the sky.

Condensation nuclei

Dust, smoke, etc. Ocean salt crystals which serve as hygroscopic