Evaporation of Rain Falling Below a Cloud Base Through a Deep Atmospheric Boundary Layer Over an Arid Region

[摘要] The evaporation of rain falling through a dry subcloud layer was investigated by using a one-dimensional, time-dependent model only including sedimentation and evaporation. The model assumed a stratiform-type; weak rain under a condition of a dry, deep atmospheric boundary layer typical of the northwest China desert region in summer. Two kinds of experiments were conducted. In the first experiment, the air was assumed to be at rest. With a medium rain intensity (9.5mmh-1) surface rain occurred at about 1h after rain started at the model top, whereas with a light rain intensity (0.97mmh-1) surface rainfall occurred at about 11.5h. The amount of rain depleted by evaporation varied widely according to the fall distance from the top and rain intensity. With a constant amount of total rain provided at the top, the amount of evaporated rain increased with rain intensity. In the second experiment, constant downward vertical velocity was prescribed to examine the effect of subsidence warming on the rain evaporation. Only a descent of a few tens of cms-1 significantly enhanced the rain depletion. Compared with the surface observations in the desert, it was suggested from the model results that evaporation of rain is a dominant cause of the observed changes typical of a desert rain event.

[学科分类] 大气科学