Time of Formation and Burn Off of Nocturnal Inversions at Detroit

Abstract

Four resistance thermometers which are installed on the WJBK-TV tower in Detroit provide continuous records of the temperatures at heights of 20, 300, 600, and 870 ft. From these records, times of formation and burn off of nocturnal inversions have been logged for the period 1 December 1956 to 31 March 1958. Time of formation, defined as appearance of an inversion between 20 and 300 ft, has been related to time of sunset. When this is done two regimes appear, as follows. During the 5 months, January through May, inversions tend to form about 2 hours after sunset. During the 5 months, July through November, they tend to form at sunset. The months of June and December appear to be transitional months. Time of burn off, defined as time of disappearance of an inversion from the layer 20 ft to 870 ft, has been related to time of sunrise with the following results. During the interval April through August burn off occurs most frequently about 3 hours after sunrise. During the interval 1 September to 31 March, burn off occurs about 2 hours after sunrise.