The SALR depends on the moisture content => the more moisture air contains the slower it will cool.
We use SALR = 1.8ºC/1000 ft in the mid latitudes. Close to the Equator where the air is warm and can contain a lot of moisture. The SALR, however, can be as low as 1ºC/1000 ft.
At the poles where it is very cold, and the air cannot hold much moisture. The SALR can be 2.8ºC/1000 ft as it is virtually dry.
As we go up in the atmosphere the air gets colder and cannot hold the same moisture, so the SALR varies with height. And, with increasing altitude, it tends to become equal to DALR – CIRRUS will be found at those levels.
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