Moisture, Adiabatic Process, Latent Heat, Humidity

Question 1

what are some characteristics of water in the atmosphere?

Answer 1

• a minor, variable gas (0-4%)
• mostly in lower troposphere and mostly from ocean
• transported high by clouds
• transported horizontally by winds
• large fluctuations in concentration, spatially and temporally

Question 2

is water an ideal gas? what is an ideal gas?

Answer 2

• yes
• ideal gas: molecules behave elastically, don’t exchange energy
• volume and pressure are proportional to the number of molecules present

Question 3

partial pressure and what determines it?

Answer 3

the pressure contributed by a single gas in a mixture of gases
- amount of a given gas determines partial pressure

Question 4

what is atmospheric pressure at sea level and how to calculate partial pressure?

Answer 4

at sea level = 1013.2 mb (let’s say 1000)
nitrogen is 78% so so partial pressure is 780 MB, and water is 0-4 mb

Question 5

why is the amount of vapor in an air mass important to it’s mass or density?

Answer 5

because mass is directly related to molecule weight of combined gases

Question 6

which is lighter, moist or dry air?

Answer 6

moist air because water vapor molecules are lighter than other dry air molecules such as nitrogen

Question 7

phase changes:
freezing, melting, evaporation, condensation, deposition, sublimation

Answer 7

freezing = liquid to solid
melting = solid to liquid
evaporation = liquid to gas
condensation = gas to liquid
deposition = gas to solid
sublimation = solid to gas

Question 8

latent heat

Answer 8

energy involved in a phase change of water
- to go from less to more active, you need to get molecules moving faster, thus latent heat is used

Question 9

how much latent heat is released when water vapor condenses? how about during a hurricane?

Answer 9

• 600cal/gram (enough to raise temp of 2.5tsp from freezing to boiling)
• equivalent to 400 20-megaton nuclear bombs, or enough for all USA electrical consumption for 1/2 year

Question 10

humidity

Answer 10

measure of amount of water vapor in atmosphere

Question 11

absolute humidity

Answer 11

• mass of water vapor/volume of air
• g/m^3
• affected by changing volume

Question 12

specific humidity

Answer 12

• mass of water vapor/ total mass of air
• g/kg
• not affected by volume changes
• mixing ratio

Question 13

mixing ratio

Answer 13

• mass of vapor/mass of dry air
• g/kg
• similar to specific humidity
• both SH and MR are constant unless moisture changes

Question 14

relative humidity

Answer 14

• vapor content of air mass/vapor content at saturation
• dependent upon vapor content and temperature
• expressed as a percent
• RH = vapor pressure/saturation vapor pressure

Question 15

saturation vapor pressure

Answer 15

max partial pressure for a given temp

Question 16

why does warm air have a greater capacity for storing moisture?

Answer 16

because as temp increases, molecules move faster, so water vapor is moving so quickly it doesn’t condense out

Question 17

as temp increases, relative humidity___.

Answer 17

decreases

Question 18

how would you increase relative humidity?

Answer 18

add moisture or decrease temp

Question 19

dew point

Answer 19

temp to which parcel must be cooled for water vapor to condense into water

Question 20

frost point

Answer 20

when dew point falls below freezing

Question 21

what does adiabatic mean?

Answer 21

without heat - temp changes without adding or removing heat

Question 22

expansion causes ____, compression causes ____

Answer 22

cooling, warming

Question 23

dry adiabatic lapse rate (DAR)

Answer 23

• rate at which dry air changes temp as it rises
• DAR = 10C/1000m

Question 24

moist adiabatic lapse rate (MAR)

Answer 24

• rate at which air at saturation changes temp as it rises
• MAR = 6C/1000m (technically 4-9.9C)

Question 25

why is MAR < DAR

Answer 25

because latent heat is released by condensing water

Question 26

lifting condensation level (LCL)

Answer 26

where air moving up the atmosphere will cool at the DAR until it reaches condesation (aka clouds form), air then moves up at the MAR

Question 27

environmental lapse rate (ELR)

Answer 27

• actual decrease in temp with increase in altitude at a given location
• ELR ~ 6.4C/1000m
• varies by local conditions

Question 28

stability

Answer 28

a measure of the tendency for vertical motion to continue in the direction of displacement from a starting point

Question 29

stable conditions

Answer 29

• ELR<MAR<DAR
• air mass will be cooler and denser than surrounding air
• resists

Question 30

unstable conditions

Answer 30

• ELR>DAR>MAR
• parcel is warmer and less dense
• does not resist

Question 31

conditionally unstable

Answer 31

• DAR>ELR>MAR
• resists if unsaturated

Question 32

absolutely unstable

Answer 32

-ELR>MAR>DAR
- does not resist

Question 33

what are two ways to promote stability

Answer 33

1. cool surface - loss of LW at night or advection of cool air
2. warm upper atmosphere - under high pressure, sinking air will warm

Question 34

what are two ways to promote instability?

Answer 34

1. heat surface - daytime heating, advect warm air
2. cool air aloft

Question 35

when is air typically most and least stable?

Answer 35

most: evening and early morning
least: mid-afternoon