Atmospheric MoistureAtmospheric Moisture

What is Atmospheric MoistureWhat is Atmospheric Moisture

Changing forms Changing forms of waterof water• Energy absorbed Energy absorbed

and lostand lostLatent EnergyLatent Energy

SublimationSublimation – solid (ice) – solid (ice)

turns to water vapor.turns to water vapor.

Ex: dry ice, add to clouds &Ex: dry ice, add to clouds &

make bigger (dry and cold)make bigger (dry and cold)

DepositionDeposition – water vapor – water vapor

changes directly to ice.changes directly to ice.

Ex: snow formationEx: snow formation

in cloudsin clouds

HumidityHumidity

Humidity – Humidity – Amount of water vapor in the Amount of water vapor in the atmosphere.atmosphere.• Controlled by rates of condensation and Controlled by rates of condensation and

evaporationevaporation• As the temperature of the air increases, the more As the temperature of the air increases, the more

water vapor the air can holdwater vapor the air can hold

Relative Humidity –Relative Humidity – ratio of the amount of ratio of the amount of water vapor in the air to the amount of water water vapor in the air to the amount of water vapor it can hold. (saturatedvapor it can hold. (saturated at equilibrium) at equilibrium)

Absolute HumidityAbsolute Humidity• Mass or actual amount of water vapor in Mass or actual amount of water vapor in

the airthe air Calculating Absolute HumidityCalculating Absolute Humidity

Absolute humidity = Absolute humidity = mass of water vapor (grams)mass of water vapor (grams)

volume of air (cubic meters)volume of air (cubic meters)

It’s hard to measure

due to the changing/shifting of

the air!!!

Probably result of the temperature and pressure

Dew PointDew Point Dew pointDew point – The temperature to which air – The temperature to which air

must be cooled to reach saturation. must be cooled to reach saturation.

Below 32º F, dew is frozen = frostDew- moisture that forms at dew point

Measuring HumidityMeasuring Humidity PsychrometerPsychrometer – instrument used to measure – instrument used to measure

relative humidity.relative humidity. Try to better predict weather conditionsTry to better predict weather conditions Consists of two thermometersConsists of two thermometers

• One damp and one dryOne damp and one dry• Absorption and Evaporation ofAbsorption and Evaporation of

MoisterMoister• Compare the temperature Compare the temperature

readingsreadings• Calculate Relative HumidityCalculate Relative Humidity

If no difference thenIf no difference then

atmosphere is saturatedatmosphere is saturated