Answer
A parcel of air travels upwards ----- Air expands and cools at dry adiabatic rate----- Parcel of air cools to dew point ----- Air continues to cool at wet adiabatic rate.
Step-by-step explanation:
The correct order is as follows
A parcel of air travels upwards ----- Air expands and cools at dry adiabatic rate----- Parcel of air cools to dew point ----- Air continues to cool at wet adiabatic rate.
An adiabatic process is one which involves no heat exchange between the air parcel and the surroundings. When a parcel of air is lighter then it starts to move upwards. It gradually cools since there is no heat exchange between the surrounding air with the air parcel (Also because in troposphere, there is decrease in temperature with altitude). This cooling is called dry adiabatic lapse rate and is usually 10°C/ km for unsaturated air.
Since the decrease in temperature is taking place, condensation takes place. Then the air parcel cools to the dew point. Since the heat within the air parcel was not able to be released since it is an adiabatic process, so during condensation that heat is released, which enhances the cooling even more, such that it becomes wet adiabatic lapse rate (5°C/km). The heat is released due to change in state of the water due to condensation taking place.