Atmospheric Moisture - Chap 6 Flashcards
Absolute humidity
(Upside down A - V)
Mass of water vapor in given VOLUME of air
(expressed as grams water/cubic meter air)
Specific Humidity
Mass of water vapor in given MASS of air (grams water vapor per kg of air)
Saturation specific humidty
maximum specific humidity at a given temperature
Vapor pressure
contribution of water vapor to total atmospheric pressure
(saturation vapor pressure - max vapor pressure at given temp)
How to calculate relative humidity
(actual water vapor in air / capacity) * 100
Factors affecting relative humidity
amount of evaporation + condensation (affects numerator)
temperature (affects capacity aka denom)
Temperature + relative Humidity relationship
INVERSE
increase in temperature –> decrease in relative humidity
WHY? Increasing temperatures INCREASE capacity to hold water (bigger denom) making overall fraction smaller
Dew point temp
temperature air must cool to saturate
sensible temperature
temperature person’s body feels
what impacts sensible temp
actual air temp, relative humidity, dew point, wind
Condensation
opposite of evaporation, occurs when air is saturated BUT need to have a surface for condensation to occur on
(air can become supersaturated if no surface is available + cooling continues)
Condensation nuclei
tiny particles (particulates) in air
hydroscopic SO serve as collection points for water molecules –> eventually form raindrops
What is the only prominent mechanism for cloud development + rain
adiabatic cooling
(air rising, pressure decreases + expands and cools)
Dry adiabatic rates
when parcel of unsaturated air rises, it cools at rate of 10 degrees C/1000 meters
Lifting condensation level
when parcel of air rises enough to become saturated, start condensation, form clouds
Saturated adiabatic rate
ABOVE LCL
slower cooling bc latent heat released from condensation counteracts the adiabatic cooling,
~6 deg C/1000 meters
Why can’t clouds form going DOWN
Adiabatic warming = descending air warms, which increases water vapor capacity SO condensation will never happen –> no clouds
3 cloud forms
1) Cirriform
2) Stratiform clouds
3) cumuliform clouds
cirriform (lock of hair)
thin, high, ice crystals instead of water droplets
Stratiform (spread out)
grayish sheets covering most of sky, rarely broken into individual units
cumuliform (heap)
massive rounded, with flat base + tend to be very tall
Cloud names
if they have “nimb” in it –> produce precipitation
4 types of fog
1) radiation fog
2) advection fog
3) upslope (orographic) fog
4) evaporation/steam fog
radiation fog
forms when ground radiates heat at night –> air warms up + rises away, replaced by cooler air that turns into fog
collects in low areas
advection fog
develops when warm, moist air ADVECTS (horizontally moves) over cold surface (snow covered ground, ocean current)
air moving from sea to land most common source of advection fog
upslope (orographic) fog, oro = mountain
created by adiabatic cooling when humid air climbs mountain/slope
evaporation/steam fog
water vapor added to cold air that is near saturation
occurs when cold air flows over warm body of water
4 types of atmospheric lifting
Convective, orographic, frontal, convergent
Convective lifting
Parcel of air heated by ground bc of convection + rises by convective lifting
expands + reaches dew point temperature, condenses, forms cumulus cloud
convective precip = showery w. fast large raindrops
orographic lifting
occurs when wind encounters mtn, forced to go up by orographic lifting –> produces precip if rising air cooled to dew point
rain shadow
occurs bc orographic lifting essentially stops climbing up + then starts descending –> leads to adiabatic warming + cloud goes poof
frontal lifting
caused by unlike air masses meeting, forming a front (unlike air masses DO NOT mix)
warm air rises over cool air, adiabatically cools, forms clouds + precip
*characteristic of midlatitudes bc of meeting grounds for cold polar air + warm tropical air
Convergent lifting
when air converges –> general uplift –> causes instability + produces showery precipitation
common in ITCZ + in cyclonic storms
