Lapse Rates MET

There are three lapse rates you need to know: ISAISA —International Standard Atmosphere (2° / 1000 ft), the dry adiabatic lapse rate (3° / 1000 ft) and the saturated adiabatic lapse rate (1.8° / 1000 ft, but which varies - see below).

The ISAISA —International Standard Atmosphere rate is a standard for performance measurement; it does not correspond to anything in the "real world." Dry air cools at 3° / 1000 ft. If the air is saturated, that means that water vapour is condensing, warming the air, so you can think of the saturated lapse rate as the dry rate (3° / 1000 ft) but warmed slightly due to condensing. The amount of warming depends upon the amount of water vapour in air, so, where there is little water vapour, such as at altitude and the poles, there will be little warming and the SALRSALR —Saturated Adiabatic Lapse Rate is almost the DALRDALR —Dry Adiabatic Lapse Rate (sometimes 2.9° / 1000 ft). Where there is lots of water vapour (sea level at the Equator) there will be lots of warming. The average of these figures is taken to be 1.8° / 1000 ft.