Water in the Atmosphere

I. EvaporationA. Variables that affect evaporation rate

1. Air Temp a. Inc Air Temp = Inc Evap

2. Water Tempa. Inc Water Temp = Inc Evap

3. Winda. Inc Wind = Inc Evap

4. Surface Areaa. Inc S Area = Inc Evap

5. Water Vapor in Air (Humidity)a. Inc Water Vapor = Decreased Evap

II. Energy Changes

A. Evaporation1. Energy is absorbed

2. Cooling process, water takes in energy from surroundings

B. Condensation1. Energy is given off

2. Warming process, water releases energy to surroundings

III. Water in AtmosphereA. Saturated Air

1. Air holding as much water vapor as possible (warm air can hold more water)

B. Dew Point1. Temperature the air must be cooled to in

order to become saturated2. As air temp and dew point temp get

closer together, air becomes more saturated and the chance for precipitation increases

3. Measured using a psychrometer and Reference Tables

III. Water in Atmosphere

C. Relative Humidity1. Comparison between the ACTUAL

amount of water vapor and the MAXIMUM amount it could hold at that temp

2. Saturated air = 100% humidity

3. Greater the humidity, less evaporation occurs

III. Water in Atmosphere

4. If air temp and dew point are equal, Relative Humidity (RH) = 100%

5. If amount of water vapor in air stays the same, the RH will decrease as temp increases

Temperature

Rel

Hum

idity

IV. Water Vapor and Air PressureA. Moist air weighs less than dry air

1. Water molecules replace heavier Nitrogen molecules

B. Moist air = Low Pressure

C. Higher Humidity = Lower Pressure

Rel Humidity

Air

Pre

ssur

e

V. Water Leaving AtmosphereA. Condensation

1. Water Vapor to liquid

B. Sublimation1. Change directly from gas to solid (vice

versa) ex. CO2

V. Water Leaving Atmosphere

C. Conditions needed for Condensation1. Water in atmosphere

2. Air MUST be cooled to dew point

3. Need surfaces for condensation to forma. Dust in air gives surface for clouds to form

V. Water Leaving AtmosphereD. Conditions caused by condensation

1. Dewa. Temp at ground reaches dew point, above

freezing, forms on solid surfaces

2. Frosta. Same as dew but temp below freezing

3. Foga. Cloud at ground level, when air temp close to

ground reaches dew point

4. Cloudsa. Water condenses on dust above ground levelb. Air cools as it rises (less air pressure so it

expands)

DEW

CLOUDS

FOG

FROST

VI. Adiabatic Cooling / WarmingA. Cooling / Heating air w/o removing

energyB. Cooling

1. As air pressure decreases, the air expands as it rises

2. There are fewer molecules in the same volume of space so there is less Kinetic energy, so temp decreases

C. Heating1. As air pressure increases, the air

compresses and increases temp

VII. Methods of Cloud FormationA. Need rising air to cool air to dew pointB. Orographic Effect

1. Clouds form as air rises up mountain, hill, plateau

2. Lake Effect Snow

VII. Methods of Cloud FormationC. Fair Weather Clouds

1. Energy is radiated from the ground leading to convection currents

GROUND

INSOLATION

TERRESTIAL RADIATION (HEATS AIR)

Warm air RISES (less dense)

Cools as it rises (adiabatic cooling)

Condensation Level

Air reaches Dew Point (becomes saturated) RH = 100%, cloud forms

VII. Methods of Cloud FormationD. Lifting Air at Frontal Boundaries

1. Cold Front – leading edge of cold air mass

VII. Methods of Cloud Formation2. Warm Front – leading edge of warm air

mass

VIII. PrecipitationA. Cloud droplets must “clump” together

until they become heavy enough to begin falling

IX. Atmospheric ProblemsA. Greenhouse Effect (Theory)

1. Glass from a greenhouse traps the infrared radiation and temps rise

2. Gases in atmosphere can do the same (CO2, CFCs and methane)

3. CO2 is increasing froma. Burning fossil fuelsb. Deforestation (cutting down rain forests)

4. Effects on Eartha. Rising Tempsb. Droughts in food growing regionsc. Melting of polar ice = rise in ocean levels

IX. Atmospheric Problems

B. Depletion of Ozone Layer1. Caused by CFCs breaking down ozone

2. Makes increased UV rays hitting Eartha. Increased skin cancer

b. Eye damage

3. Solutionsa. Different aerosol propellants

b. Use less styrofoam

c. Different types of refrigerants