Diurnal variability of the hydrologic cycle in a general circulation model

Abstract

This paper presents an analysis of the diurnal and semidiurnal variability of precipitation, evaporation, precipitable water, horizontal moisture flux convergence, cloudiness, and cloud radiative forcing, as simulated by the Colorado State University General Circulation Model (GCM). The model produces an afternoon precipitation maximum over land in warm rainy regions, such as the tropics and the midlatitude summer continents, and an early morning maximum over the oceans far from land. An oceanic diurnal cycle of precipitation occurs even in the absence of neighboring continents and tends to have a morning maximum. Several experiments have also been performed with a one-dimensional version of the GCM, in which time-dependent large-scale vertical motion can be prescribed. The results show that even in the absence of any systematic daily variation of the large-scale vertical motion, the model produces a diurnal cycle of precipitation with an amplitude of about 1 mm day-1, and a morning maximum. -from Authors