It refers to the natural fall in temperatures with an increase in altitude OR a rise in temperatures with a decrease in altitude. As warm air rises, it expands and cools leading to a fall in temperatures. The increase in temperature or heat is caused by the compression of the air as altitude falls.
Types of Lapse Rate:
The lapse rate is described in three (3) ways:
- Environmental lapse rate It is the rate at which temperatures change with an increase or a decrease in altitude. It is the vertical distribution of the temperature of a given geographical location at a particular period
- Dry adiabatic lapse rate It is the rate at which dry air cools as it rises without affecting the temperature of the surrounding atmosphere. Dry air cools at a faster rate of 1-degree centigrade per 100 metres of ascent
- Saturated (Wet) adiabatic lapse rate refers to the rate at which air saturated with water vapour cools as it rises to greater heights (higher levels) of the atmosphere. Saturated (humid) air cools at a rate which is slightly lower than that of dry air i.e. between 0.3-degree centigrade – 0.9-degree centigrade per 100metres of ascent.