zone thermale

CONT: Silas McDowell (1795-1879) was a southern pomologist and a botanist of renown ... during the 1850s. ... He was the originator of the ""thermal belt"" concept which is a zone on a mountainside where frost and freezes are less common than in the valleys and on the mountaintops.
OBS: The air flowing down the slopes is warmed by mixing with the air above ground level and to some extent also by adiabatic compression. The frostless zone is not a fixed belt but varies in level from night to night and season to season according to the initial temperature, the length of the night, and the clearness of the sky. Its lower limit is sometimes clearly marked by the upper limit of frost damage to crops, following the hillsides at a small angle to the horizontal.