Water in the Atmosphere Chapter 18

H 2 O exists in atmosphere in all three states of matter…

Solid: snow hail ice

Liquid: rain and cloud droplets

Gas: invisible H2OH2O vapor

H 2 O may change from one state to another:

Melting: from solid ice to liquid H 2 O

Freezing: liquid H 2 O to solid ice

Evaporation: from liquid H 2 O to H 2 O vapor

Condensation: from H 2 O vapor to liquid H 2 O

Sublimation: change from solid to H 2 O vapor Example: Dry ice

a measure of the energy in molecules the more energy the molecules have, the hotter it feels

isotherm: lines on a map that connect places that have the same temperature

thermometer: instrument that measures temperature alcohol and mercury thermometers used (mercury more accurate)

water freezes at: 0ºC or 32 ºF water boils at: 100ºC or 212ºF

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

Warmer the air, the more H 2 O 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

Dew point: the temperature at which water vapor condenses Dew, clouds, and fog forms If dew point is below freezing, frost will form

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

Three main cloud types:

CIRRUS: - thin, feathery, made of ice crystals - form at high altitudes - seen when weather is fair, but can mean rain or snow

STRATUS Low sheets or layers; gray and smooth Block out the sun Associated with rain and drizzle

CUMULUS Piled in thick, puffy masses Formed by vertically rising air currents Usually mean fair weather

Other cloud types:

Cirrostratus

Stratocumulus

Cirrocumulus

Altocumulus

Nimbostratus

Cumulonimbus: large cloud that produce LIGHTNING, THUNDER, HEAVY SHOWERS = Thunderstorms

Precipitation: Water that falls from the atmosphere to the earth Occurs when cloud droplets grow into drops heavy enough to fall to Earth

FORMS OF PRECIPITATION Drizzle: fine drops, very close together, fall slowly ….less than 0.5mm diameter Rain drops: larger, farther apart, fall faster… 0.5mm to 5mm diameter Snow: falls in clumps of six-sided crystals Sleet: pellets of ice tha fall to the ground when raindrops fall through freezing air

Hail: irregular balls or lumps made of layers of ice forms in cumulonimbus clouds-

Acid rain: 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

Rain gauge: instrument used to measure the amount of rainfall

Condensation nuclei: suspended particles that provide the necessary surfaces for cloud forming condensation.