An Examination of the Effects of Explicit Cloud Water in the UCLA GCM

[摘要] The effects of explicit cloud water are examined by adding the mixing ratios of cloud ice and cloud liquid water to the prognostic variables in the UCLA GCM. A simple cloud model and the published radiation schemes are incorporated in the model. Besides a grid-scale condensation process, the other source of cloud ice and cloud liquid water is the detrainment from the cumulus. The detrained cloud ice and cloud liquid water are obtained by the microphysical calculation in the Arakawa-Schubert cumulus scheme. The results are compared with the observations, concerned with cloudiness, planetary albedo, OLR and the dependence of cloud water content on temperature. The dissipation process of cloud ice with use of a realistic ice fallspeed produces realistic simulations. Cloud ice detrained from the cumulus simulates anvil clouds in the tropics. These clouds coexist with those due to grid-scale condensation, such as thin cirrus. Even at low temperatures, anvil clouds have dense cloud ice content which is one to two order larger than that of clouds due to grid-scale condensation. Anvil clouds produce low OLR, high planetary albedo and strong shortwave absorption in the tropical convective regions. Grid-scale condensation is active in moist environment due to the sublimation of the detrained cloud ice, and produces a net positive heating rate in the upper troposphere. The sublimation and melting of cloud ice, and the evaporation of rain produce a net cooling rate in the lower troposphere.

[学科分类] 大气科学