Moisture in the Atmosphere Flashcards
What three factors is evaporation governed by?
- Amount of moisture already in the air; 2. Availability of moisture; 3. Availability of heat energy
How does wind contribute to evaporation?
It is a minor factor that replaces saturated air with unsaturated air
What is the main source of evaporation for the atmosphere?
Warm oceanic areas
At what point will evaporation into overlying air cease?
When the air becomes saturated
What does vapor (e) pressure represent?
The amount of water held in the air
What does saturated vapor pressure (es) represent?
The maximum amount of water vapor which an air parcel can hold at the same temperature
Water will continue to evaporate until (?) = (?)
E = Es
Why is heat required for evaporation?
To provide the latent heat of evaporation
What wind direction in respect to Uk geographic location would bring cold and dry air?
North or east winds
What wind direction in respect to UK geographic location would bring warm, moist air?
West or South West
What is relative humidity defined as?
RH is a measure of the %amount of moisture in the atmosphere
How is relative humidity calculated?
e/es * 100
When does condensation occur
This is when vapour pressure is equivalent to saturated vapour pressure, (e=es), and relative humidity is 100%
When is molecular kinetic energy greater?
At a higher temperature
What is the dew point temperature?
The temperature at which condensation occurs (RH=100% and e=es).
What is a high Td indicative of?
Moister air
What is a low Td indicative of?
Dryer air
What is Adiabatic process
Lifting and cooling to form condensation can be considered adiabatic. This is when no heat energy is exchanged with outside air.
How does Adiabatic cooling occur?
As an air parcel rises it expands because the surrouding pressure gets lower; when it expands work is done and therefore heat is lost. This causes internal energy to decrease and cooling of the air to occur.
What is adiabatic heating
The reverse of adiabatic cooling - the effects of descending air.
How does adiabatic heating occur?
As the iar subsides, it contracts due to increasd pressure; then work is done and warms the air.
What sort of mass air movement can adiabatic heating be associated with?
Links to anticyclone behaviors because the increasing temperature, due to the decent, means that the air tends to dry out as it warms
What are the main characteristics of ‘stable air’
It doesn’t rise from free convection; this is when air is colder below that the air above.
What does air stability depend on?
The temperature of the rising air relative to the temperature of the stationary surrounding air.
What does air stability determine?
Whether clouds form when air is uplifted and which type of cloud forms.
What is potential instability of air?
A layer of air which is forced to rise may become unstable and freely convect in certain circumstances.
How does potential instability occur?
If the DALR > ELR then the air is stable and cooling more quickly than the air it travels in; however if the DALR < ELR then the air is unstable as it cools less quickly than the air it passes through.
What is stability a function of in terms of the ocean?
A function of density - which is function of temperature and salinity.
What is the Mass mixing Ratio?
The mass of water vapour in grams per kilogram of dry air.
When does the dew point temperature occur?
Temperature at which saturation occurs if air is cooled at constant pressure without addition or removal of vapour.
What happens when the air pressure and dew point are equal?
The relative humidity is 100%
What 4 types of instrument can atmospheric moisture be measured with?
Wet-bulb thermometer; Psychrometer; Dew-point hygrometer; Hydrograph
How does a wet-bulb thermometer work?
Bulb of a standard thermometer wrapped in Muslin, which is kept moist by a wick from a reservoir of pure water. Evaporative cooling of the wet bulb gibes a reading that can be used in conjunction with a simultaneous dry-bulb temperatue
What is a dew-point hygrometer.
Detects when condensation first occurs on a cooled surface.
What is the latent heat required to evaporate 1kg of water at 0C?
2.5 * 10^6 J
How is the energy requirded for evaporation obtained?
From the removal of heat from immediate surroudings - causing apparent heat loss, (latent heat).
What factors does the rate of evaporation depend on?
The differecne betwen the SVP at the water surface and the vapour pressure of the air and the existence of a continual supply of energy to the surface.
How does wind velocity affect evaporation rate?
The wind is generally associated with the advection of unsaturated airm which will absorb the available moisture.
