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Abstract The diurnal variation of precipitation is discussed and attention is drawn to the high frequency of night‐time rains over central U.S.A. A new theory for explaining this nocturnal maximum and the relatively low activity of precipitation in daytime is proposed by suggesting that cooling and heating processes during the night and the day set up a large‐scale circulation system east of the Rocky Mountains. The existence of this circulation system is proved by computation of the changes which occur in the convergence‐divergence field at 4,000, 10,000 and 18,000 ft in the free atmosphere.
Bleeker et al. (Sun,) studied this question.