Clouds

            The first widely accepted system for cloud classification was devised by English naturalist Luke Howard in 1803. It divided clouds into four basic categories:

1.    Cirrus—thin, wispy clouds of ice

2.    Stratus—layered clouds

3.    Cumulus—clouds having vertical development

4.    Nimbus—rain-producing clouds

Generalized Cloud Chart:

Our current classification scheme is a modified version of Howard’s, retaining his four categories and also allows new combinations. The ten principle types of clouds that result are then grouped according to their height and form:

High Clouds (greater than 19,000 ft)	Cirrus (Ci)	Thin, white, wispy clouds of ice resembling mares’ tails.
	Cirrostratus (Cs)	Extensive, shallow clouds somewhat transparent to sunlight, producing a halo around the Sun or Moon.
	Cirrocumulus (Cc)	High, layered cloud with billows or parallel rolls.
Middle Clouds (6,000 ft to 19,000 ft)	Altostratus (As)	Extensive, watery, layer clouds composed of water droplets. Allows some penetration of sunlight but Moon or Sun appears as bright spot within cloud.
	Altocumulus (Ac)	Shallow, mid-level cloud containing patches or rolls, often arranged in bands. Generally more opaque and having less distinct margins than cirrocumulus.
Low Clouds (below 6,000 ft)	Stratus (St)	Uniform layer of low cloud ranging from whitish to gray.
	Nimbostratus (Ns)	Low cloud producing light precipitation. Produces darker skies than altostratus.
	Stratocumulus (Sc)	Low-level equivalent to altocumulus with some vertical development.
Clouds with Extensive Vertical Development (may extend through mmm moo atmosphere)	Cumulus (Cu)	Detached billowy clouds with flat bases and moderate vertical development. Sharply defined boundaries.
	Cumulonimbus (Cb)	Clouds with intense vertical development with characteristic anvil. May be tens of thousands of meters thick. Appear very dark when viewed from below. Can create violent weather.

Unusual Clouds:

─     Lenticular Clouds—waves formed by the passage of air over a topographic barrier.

─     Banner Clouds—isolated atop mountain peaks

─     Mammatus—found in margins of cumulonimbus clouds, formed by downdrafts, and sometimes are distorted by complex motions.

─     Nacreous Clouds—stratus clouds only observed at high latitudes.

─     Noctilucent Clouds—in the mesosphere, can illuminate the sky at high latitudes during the twilight hours. Noctilucent clouds

Other:

─   Aircraft Contrails—A type of ice cloud, know as contrails, is frequently caused by jet aircraft. The very hot engine exhaust contains considerable water vapor as a result of fuel combustion, and turbulence in the wake of the aircraft rapidly mixes the exhaust with the cold, ambient air. The mixing of warm, moist air with cold air can lead to saturation and, in this case, the rapid formation of ice crystals.

Forecasting: Why Clouds Have Clearly Defined Boundaries

Understanding Weather and Climate (7th Edition) (MasteringMeteorology Series) by Edward Aguado, James E. Burt

Focus on Aviation: Icing

Understanding Weather and Climate (7th Edition) (MasteringMeteorology Series) by Edward Aguado, James E. Burt

Properties of the Atmosphere

Ø Temperature

̶        A measure of the average speed that molecules move in a substance (solid, liquid, gas)

̶        The average speed of the molecules will increase in the colder substances and decrease in the warmer substances.

̶        Temperature is related to the energy of motion of molecules

̶        Usually decreases rapidly upward away from the earth’s surface (about 12 km/7 miles)

̶        Above about 12 km the temp increases with height, then begin to decrease again about 50 km/31 miles

̶        Troposphere = layer of air in the lower atmosphere where temp decreases with height

̶        Stratosphere = layer above the troposphere where temp increase with height because of the absorption of the ultraviolet radiation by ozone in that layer

̶        Tropopause = boundary between troposphere and stratosphere

̶        Tropical storms grow to greater heights than storms that form in the middle of latitude and Polar Regions because the tropopause is higher in the tropics

Ø Pressure

̶        Force applied by air on a unit area of surface.

̶        Equivalent to the weight of a column of the air above a unit area

̶        Millibar (mb) = 1,000dynes/centimeter^2 or to a hectopascal (100 pascals)

̶        Average pressure at sea level is 1013.25 mb - pressure decreases rapidly while moving away from the earth’s atmosphere

̶        Measured with a Barometer–simplest to use is the mercury barometer

̶        Measurements are made worldwide every hour

Ø Moisture / Moisture Variables

̶        Clouds from water vapor (invisible gas composed of individual water molecules)

̶        Water vapor is mixed with other gases in the atmosphere (such as, nitrogen & oxygen)

̶        Vapor Pressure =  force per unit area applied by only the water vapor molecules (ranges from 0 in a cold atmosphere to 60mb in a humid tropical atmosphere)

̶        Atmosphere reaches saturation when the invisible vapor condenses into visible cloud droplets

̶        Saturation Vapor Pressure = vapor pressure at which the atmosphere becomes saturated

̶        The atmosphere's capacity for water vapor (and saturation vapor pressure) depends on temperature

Ø Phase Changes and Clouds

̶        Air contains water vapor and clouds in the air are composed of liquid and ice particles

·        Vapor to water = condensation

·        Water to ice = freezing

·        Vapor to ice = deposition

·        Ice to vapor = Sublimation

·        Water to vapor = evaporation

·        Solid to liquid = melting

·        Latent heat = hidden heat required for a phase change

Ø Wind

̶        The movement of air (direction and speed)

̶        Anemometer = device to measure wind speed

̶        Meteorologists depict wind speed and direction using wind barbs on a staff

Continually orbit around the earth in the general circulation, the large-scale pattern of prevailing winds and pressur