Lecture 3: Humidity and Condensation

hydrologic cycle

the cycle of moving and transforming water molecules from liquid to vapor and back to liquid (or solid then liquid)

wind

transports moist air to other regions where vapor turns back to liquid

percolation

allows a portion of water in hydrologic cycle to infiltrate into the ground, forming groundwater

transpiration

when plants give up moisture

puddle or runoff

what happens to water that does not soak in

15%: continental evaporation and transpiration; 85%: from oceans

breakdown of global evaporation

saturation

when molecules escaping = molecules returning

enhance

Does wind enhance or weaken evaporation?

condensation nuclei

on which water vapor molecules form tiny liquid cloud droplets

cool air

is saturation more likely to occur in cool air or warm air

mass of water vapor / volume of air

absolute humidity formula

absolute humidity

represents water vapor density

fluctuation of air volume due to air pressure

Is absolute humidity commonly used in atmospheric studies? Why or why not?

less, higher

high pressure, _______ air volume; low pressure, ________ air volume

mass of water vapor / total mass of air

specific humidity formula

mass of water vapor / mass of dry air

mixing ratio formula

change in parcel size does not affect values

Are specific humidity and mixing ratio used extensively in atmospheric studies? Why or why not?

moisture spatial variation

variation of specific humidity according to latitude

highest, decreases

avg SH is ______ in the tropics, _______ as you go to higher latitudes

higher T in tropics, more vapor in air

Why is there higher specific humidity in the tropics?

Dalton’s Law of Partial Pressures

states that the total pressure in an air parcel is equal to the sum of the pressures of the individual gases in the parcel

total air pressure * % of vapor by volume

formula for actual vapor pressure

more

higher actual vapor pressure, _____ water vapor molecules

saturation vapor pressure

actual vapor pressure when the air is saturated with water vapor at a given T

air temperature; temperature determines rate of escape and return of molecules

on which saturation vapor pressure primarily depends; why?