Lecture 10 Clouds And Precipitation Flashcards
Warmer air can hold more or less water vapor?
More
Vapor pressure
- air molecules all contribute to pressure
- each subset of molecules exerts a partial pressure
- the vapor pressure is the pressure exerted by water vapor molecules in the air
Saturation vapor pressure
Is the pressure that the water vapor molecules would exert if the air were saturated with vapor at a given temperature
Saturation vapor decreases or increases with temperature?
Increases
Relative humidity
Is the ratio of the amount of water vapor actually in the air to the maximum amount of water vapor required for saturation at that particular temperature and pressure
RH (Relative Humidity) Equation
(Actual vapor pressure/ saturation vapor pressure)* 100%
The higher the dew point
The more water vapor in the air
Why so many moisture variables?
- useful conceptually
- useful in conservation equations
- useful for describing how life is affected by humidity
- useful because they can be measured
Two categories of indices
- a measure of moisture content (absolute humidity, specific humidity, mixing ratio, vapor pressure, dew point temperature)
- a measure of how near the air is to being saturated (relative humidity)
Cooling causes?
Condensation
What is a cloud?
A visible aggregate of tiny water droplets or ice crystals suspended in the air
Four basic types of clouds by their appearance
- Stratus
- Cumulus
- Cirrus
- Nimbus
Stratus cloud
Latin for “layer” sheet like clouds
Cumulus cloud
Latin for “heap” puffy clouds
Cirrus clouds
“Curl of hair” wispy clouds
Nimbus cloud
Violent rain
How to change air temperature
- absorption of heat (by radiation, conduction, sensible heat)
- mixing warm and cold air (convection)
- phase change of water (latent heat, condensation releases heat and warms the surrounding air)
A fourth category of process that changes air temperature
Adiabatic process
Adiabatic process
No interchange of heat with other objects. It involves change in pressure
We have an air parcel with pressure larger than the surrounding environment. What will happen to the air volume and air temperature?
- the air parcel will expand due to the pressure difference
- as it expands it does work to the environment
- doing work consumes energy. So, the air parcel temperature drops
The raising parcel expands and cools by
10 degrees Celsius per 1000 m
The rate with which the parcel temperature decreases with height is called?
Lapse rate
The 10 degrees/km is called the
Dry Adiabatic lapse rate
Natural mechanisms of lifting air
- orographic lifting
- frontal lifting
- convergence
- localized convection
Orographic lifting
Forced lifting along a topographic barrier like a mountain
Frontal lifting
Buoyancy deflects warm air over cold air
Convergence
Winds converge and air is forced upward
Localized convection
Buoyancy lifts warm air parcels; smaller scale
(Warm air is lighter and thus more buoyant than cold air)
Atmospheric stability
Air susceptibility to uplift
Stable
Returns to original position after displacement
Unstable
Moves farther away from its original position
Neutral
Remains in new position after being displaced
Adiabatic lapse rate of air parcel
How much air parcels temperature will change when lifted
Environmental lapse rate
Actual temperature of surrounding still air at each altitude
Environmental lapse rate is _________ than DRY Adiabatic lapse rate of air parcel
Larger
Environmental lapse rate is ________ than MOIST Adiabatic lapse rate of air parcel
Smaller
Environmental temperatures determine
Stability for raising parcels
