Atmospheric moisture and precipitation Flashcards
Why do we need the hydrological cycle?
To manage the constant great inputs and outputs of water to sustain global climate
How does evaporation transport heat?
Through latent heat
When can more water be held in the air?
At higher temperatures
What is absolute humidity?
Mass of water held by particular volume of air
What is relative humidity %?
Ratio of aired actual vapour to the maximum it could hold at that temperature
What happens to air parcels when the rise and sink?
When they rise the surrounding pressure decreases (parcel has higher pressure) so it expands, does work and cools (decreases adiabatically)
Parcel contracts when sinking and warms (goes to area go high pressure)
What is an adiabatic process?
No energy is added or taken away from system
What does a parcel of air cool at if it hasn’t reached saturation?
Dry adiabatic lapse rate
What is lapse rate?
Way temperature changes with height of atmosphere
What is saturated adiabatic lapse rate?
When parcel of air is saturated latent heat is released, slowing rate of cooling
What is needed for latent heat of melting/ vaporisation?
Energy must be applied to break the bonds
What happens to energy during sublimation, condensation and freezing?
Energy returned to atmosphere as sensible heat (warms up surroundings)
What are the different atmospheric stabilitys?
Unstable - air parcel warmer than surroundings (rise)
Neutral - air parcel same temp as surroundings (remain)
Stable - air parcel cooler (move down)
What is the lifting condensation level?
Level at which a parcel of moist air lifted dry adiabatically becomes saturated
What 4 ways is air lifted?
- Orographic lifting (over mountain)
- Frontal uplift (warm over cold air mass)
- Convectional lifting (heating of warm surface)
- Convergence and uplift
How is fog formed?
- Warm mass of air passes over cold land, lowest layers may be cooled to dew point creating fog
- Cold air moves over warm sea (advection fog)
How it radiation fog formed?
Calm clear nights, land cool lowest layers to below dew point, once fog forms upper layer of fog radiates heat away thickening the fog
How does Vally fog form?
Downslope movement of cold air (dense), if air is moist enough and cools below dew point
How does a cloud drop become a rain drop?
- cloud drop needs to be heavy enough to fall and not be held up by currents
- must not evaporate before ground
- for snow crystals must not melt
What is needed to form precipitation?
- Saturated air
- Lifting mechanism
- Condensation nuclei
What is the collision-coalescence process?
- Takes place in warm clouds
- Bigger drops fall faster and overtaken and absorbs smaller drops
- Small drops swept aside
What is the Bergeron-Findeisen process?
- Occurs in mixed ice-water clouds
- Iice crystals form on ice nuclei
- Water vapour moves towards ice crystals and makes them bigger
What are the 2 process which droplets form?
Bergeron-Findeisen proces
collision-coalescence process
What are the 3 cloud types?
Stratus clouds - sheet like (pure status clouds below 2000m)
Cumulus clouds - individual clouds with visible outline (vertical growth)
Cirrus clouds - short detached hair like clouds at high altitudes (above 6000m)
What is an alto stratus cloud?
Mid level sheet like
What is a nimbostratus cloud?
Mid level sheet like, associated with rain
What is a cumulonimbus cloud?
verticle cloud associated with rain, lower than 200m
