Water in the Atmosphere

H2O exists in atmosphere in all three states

of matter…

Solid:

snow

hail

ice

Liquid: rain and

cloud droplets

Gas:invisible H2O

vapor

H2O may change

from one state to another:

Melting:•from solid ice to liquid H2O

Freezing:

•liquid H2O to solid ice

Evaporation: •from liquid H2O to H2O vapor

Condensation: from H2O vapor to liquid H2O

Sublimation: change from solid to H2O vapor

Example: Dry ice

Water vapor enters the atmosphere from the evaporation of water from oceans, lakes,

marshes and glaciers

Dew point: the temperature at

which water vapor condenses

•Dew, clouds, and fog forms

•If dew point is below freezing, frost will form

Warmer the air, the more H2O vapor it can

hold•Humidity:

water vapor in the air

• Relative humidity:the % of moisture the air can hold relative to the amount it can hold at a certain temperature

Relative humidity=specific humidity X 100

capacity (saturated)

Psychrometer: instruments used to measure relative

humidity• Works on principle

that evaporation causes cooling

• 2 thermometers…wet-bulb and dry-bulb

• Readings show how dry the air is

Clouds: simply high fogs, mist,

or haze•Form when air above surface cools below dew point

•Shape depends on air movement that forms it

-horizontal air movement = layers-vertical air movement = piles

• Temperature above freezing – clouds drop water

• Temperature below freezing – clouds drop snow crystals

Precipitation:•Water that falls from the

atmosphere to the earth•Occurs when cloud droplets

grow into drops heavy enough to fall to Earth

Acid precipitation: acid drops that fall to the

ground- contain nitrate and

sulfate particles that come from burning fuels, volcanoes and cars

• Cloud seeding: method to cause an increase in precipitation

Condensation nuclei: suspended particles that provide the

necessary surfaces for cloud forming condensation.