CSIR NET June 2016 Q44: Meteorology
As an air parcel descends through the atmosphere, it moves into a region of higher ambient pressure. Assuming the process is adiabatic (no heat exchange with surroundings) and the parcel remains in pressure equilibrium with its surroundings, it is compressed, and adiabatic compression does work on the parcel, raising its temperature while reducing its volume.
Atmospheric pressure increases toward the surface, so as an air parcel descends from higher altitude to lower altitude, the surrounding (ambient) pressure it must equilibrate with increases. To remain in pressure balance, the parcel is compressed — its volume decreases.
Because this compression happens adiabatically (rapidly enough that negligible heat is exchanged with the surrounding air), the work done in compressing the parcel converts into an increase in its internal energy, raising its temperature. This is the same principle behind the warming of downslope (katabatic-type) winds such as Foehn/Chinook winds.
Because this compression happens adiabatically (rapidly enough that negligible heat is exchanged with the surrounding air), the work done in compressing the parcel converts into an increase in its internal energy, raising its temperature. This is the same principle behind the warming of downslope (katabatic-type) winds such as Foehn/Chinook winds.
Option 1 (volume and temperature both increase) is incorrect; volume decreases, not increases, upon descent.
Option 2 (volume and temperature both decrease) gets the temperature direction wrong; adiabatic compression raises temperature, not lowers it.
Option 3 (volume increases, temperature decreases) describes the opposite process — this is what happens when a parcel rises and expands (adiabatic cooling), not when it descends.
Option 4 is correct: on descent, increasing ambient pressure compresses the parcel (volume decreases) and adiabatic compression heats it (temperature increases).
Option 2 (volume and temperature both decrease) gets the temperature direction wrong; adiabatic compression raises temperature, not lowers it.
Option 3 (volume increases, temperature decreases) describes the opposite process — this is what happens when a parcel rises and expands (adiabatic cooling), not when it descends.
Option 4 is correct: on descent, increasing ambient pressure compresses the parcel (volume decreases) and adiabatic compression heats it (temperature increases).