Moisture, Adiabatic Process, Latent Heat, Humidity Flashcards

1
Q

what are some characteristics of water in the atmosphere?

A
  • 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
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2
Q

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

A
  • yes
  • ideal gas: molecules behave elastically, don’t exchange energy
  • volume and pressure are proportional to the number of molecules present
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3
Q

partial pressure and what determines it?

A

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

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4
Q

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

A

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

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5
Q

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

A

because mass is directly related to molecule weight of combined gases

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6
Q

which is lighter, moist or dry air?

A

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

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7
Q

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

A

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

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8
Q

latent heat

A

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

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9
Q

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

A
  • 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
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10
Q

humidity

A

measure of amount of water vapor in atmosphere

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11
Q

absolute humidity

A
  • mass of water vapor/volume of air
  • g/m^3
  • affected by changing volume
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12
Q

specific humidity

A
  • mass of water vapor/ total mass of air
  • g/kg
  • not affected by volume changes
  • mixing ratio
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13
Q

mixing ratio

A
  • mass of vapor/mass of dry air
  • g/kg
  • similar to specific humidity
  • both SH and MR are constant unless moisture changes
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14
Q

relative humidity

A
  • 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
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15
Q

saturation vapor pressure

A

max partial pressure for a given temp

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16
Q

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

A

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

17
Q

as temp increases, relative humidity___.

18
Q

how would you increase relative humidity?

A

add moisture or decrease temp

19
Q

dew point

A

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

20
Q

frost point

A

when dew point falls below freezing

21
Q

what does adiabatic mean?

A

without heat - temp changes without adding or removing heat

22
Q

expansion causes ____, compression causes ____

A

cooling, warming

23
Q

dry adiabatic lapse rate (DAR)

A
  • rate at which dry air changes temp as it rises
  • DAR = 10C/1000m
24
Q

moist adiabatic lapse rate (MAR)

A
  • rate at which air at saturation changes temp as it rises
  • MAR = 6C/1000m (technically 4-9.9C)
25
why is MAR < DAR
because latent heat is released by condensing water
26
lifting condensation level (LCL)
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
27
environmental lapse rate (ELR)
- actual decrease in temp with increase in altitude at a given location - ELR ~ 6.4C/1000m - varies by local conditions
28
stability
a measure of the tendency for vertical motion to continue in the direction of displacement from a starting point
29
stable conditions
- ELR
30
unstable conditions
- ELR>DAR>MAR - parcel is warmer and less dense - does not resist
31
conditionally unstable
- DAR>ELR>MAR - resists if unsaturated
32
absolutely unstable
-ELR>MAR>DAR - does not resist
33
what are two ways to promote stability
1. cool surface - loss of LW at night or advection of cool air 2. warm upper atmosphere - under high pressure, sinking air will warm
34
what are two ways to promote instability?
1. heat surface - daytime heating, advect warm air 2. cool air aloft
35
when is air typically most and least stable?
most: evening and early morning least: mid-afternoon