When does evaporation occur?
When energy from solar radiation hits the surface of the water or land and causes liquid water to change state to a gas.
What 4 things does the rate of evaporation depend upon?
The amount of solar energy
Availability of water
Humidity of the air
How does air humidity affect the rate of evaporation?
The closer the air is to the saturation point, the slower the rate of evaporation.
How does the air temperature affect the rate of evaporation?
Warmer air can hold more water vapour
How do all terrestrial plants lose water?
What can intercept rain as it falls?
Does evaporation use energy?
What is energy used in the form of?
Does evaporation warm or cool the surroundings?
It cools them as energy is used
What is the dew point temperature?
The temperature at which the air becomes saturated.
What happens at the dew point temperature?
Excess water in the air will condense
What is needed for condensation to occur?
Condensation nuclei or surfaces that are below the dew point temperature.
What is condensation nuclei?
Give an example of a form of condensation nuclei.
Dust, smoke, salt
What happens if the condensation nuclei or surfaces are below freezing?
The water sublimates, changing from gas to solid in the form of hoar frost.
What is condensation the direct cause of?
All forms of precipitation
When does condensation occur?
When the air temperature is reduced to dew point but its volume remains constant.
Or when the volume of air increases but there is no addition of heat (adiabatic cooling).
When does the air temperature reduce but the volume of air stay constant?
When warm, moist air passes over a cold surface.
On a clear winter’s night when heat is radiated out into space and the ground gets colder, cooling the air it is in direct contact with.
When does adiabatic cooling take place?
When air rises and expands in the lower pressure of the upper atmosphere.
When does air rise and expand in the lower pressure of the upper atmosphere?
As a result of:
The orographic effect (relief)
The frontal effect
The convectional effect
What is the orographic effect?
Air is forced to rise over hills
What is the frontal effect?
Masses of air at different temperatures and densities meet, the less dense warm air rises over the colder, denser air.
What is the convectional effect?
Localised warm surfaces heat the air above. This expands, becomes less dense and rises.
What is ablation?
Melting of ice
When does permafrost occur?
When air temperatures are so low that they freeze any soil and groundwater present.
Why does permafrost rarely occur under ice?
The temperatures are not low enough.