Water in the Atmosphere

Objectives: •What are some ways in which water condenses?•How do clouds form?•What are major cloud types?•What are the major forms of precipitation?

Humidity = Amount of water vapor in air

Warm tropical air contains more water than cold, polar air

•Relative Humidity =Ratio of the amount of water vapor in the air to the maximum amount of water vapor that can exist as that temperature.

•Expressed as a %

•Ex.: Relative Humidity is 60%, Air contains 60% of maximum amount of water vapor that can exist at that temperature

•Relative humidity = 100 %, Air is SATURATED

Relative Humidity & Dew Point

• Warmer air can hold more water

• @ night: Temps. Cool; amt. of water air can hold decrease & relative humidity increases.

• During day: air warms & humidity decreases.

(even though the total amount of water in air stays the same).

DEW POINT =

Temp. at which air is SATURATED (RELATIVE HUMIDITY 100%).

If temps. Drop further water vapor condenses (air can’t hold any more water)

Types of Condensation1. Dew – water vapor condenses on earth’s surface (leaves).2. Frost – dew point of air is below freezing.

– Water doesn’t condense. G S (ice)

3. Fog – water vapor condenses to form a cloud that is near / touching ground4. Clouds

Cloud Formation

Clouds = dense, visible mass of tiny water droplets or ice crystals (very small) that are suspended in the atmosphere.

Cloud formation:1.Warm, moist air rises in atmosphere2.Water vapor condenses when temp. drop below

dew point.3. Condensation Nuclei – also needed

Dust, salt, solid particles needed as platforms for water to condense on.

Cloud Type: Cumulus

• Cumulus Clouds – Puffy, piles/heaps of cotton balls w/ flat bottoms.

• “fair weather clouds”• Form less than 2 kms. From

ground– Cumulonimbus = Dark towering

clouds that are ass. w/ thunder storms. Grow vertically. (Anvil top) “Thunder heads”

Cloud Type: Stratus• Stratus Clouds – Flat

layers, cover much or all of sky– Nimbostratus = low

stratus that produce steady, widespread rain or snow.

– Altostratus = Middle level clouds (2000 – 6000 meters) that produce light rain or snow.

Cloud Type: Cirrus

Cirrus Clouds = Thin wispy feathery /veil like clouds made up of ice crystals.

• Clear sunny days

• Don’t produce rain … but are usu. Ahead of rain producing clouds.

• High AltitudesLink to chart: http://educ.queensu.ca/~science/main/concept/biol/b03/G08LABR8.gif

Forms of Precipitation

• Rain = liquid precip. Forms in nimbostrat. or cumulonibus clouds

• Snow = ice cystals• Hail = round, solid pieces of ice more than 5 mm

in diameter. Ice is tossed up & down in cumulonimbus clouds and get coated w/ water that freezes layers of ice.

• Sleet = Ice particles less than 5mm in diamter. Rain freezes as it falls.

• Freezing Rain = rain freezes after hitting surfaces.