Adiabatic Processes:
Humidity- the amount of water vapor present in the air.
Absolute Humidity- The amount of water vapor present in a unit volume of air.
Relative Humidity-the ration of the amount of water vapor actually present in the air to the greatest amount possible at the same temperature.
R. H = Actual Water Vapor content/ Water Vapor Capacity (Maximum Capacity that the air can hold)
Saturation Mixing Ratio- The water vapor capacity of air at given temperature.
As temperature increases, water vapor capacity of air also increases.
Dew Point Temperature-
Conceptual Framework:
As temp. of parcel of air decreases R.H. increases
When Parcel of air has cooled to the dew point of temp, it becomes saturated and condensation takes place.
With altitude pressure decreases – as parcel of air rises – it comes under low pressure – and expands.
Adiabatic – a process where the parcel temperature changes due to an expansion or compression, no heat is added or take away from the parcel.
The parcel expands since the lower pressure outside allows the air molecules to push out on the parcel walls.
Since it takes energy for the parcel molecules to push out on the parcel walls, they use up some of their internal energy in the process.
Therefore, the parcel also cools since temperature is proportional to molecular internal energy.
DAR & SAR
If a parcel of rising air is unsaturated (RH is less than 100%) it will cool at Dry Adiabatic Rate. ( 10 degrees Celsius per 1000 metres or 5.5 degrees farenheight).