Water in the Atmosphere

H2O exists in atmosphere in all three states of matter…

Solid: snow hail ice

rain and cloud droplets 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 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.