Diagnostic analyses of the ageostrophic Q vector in the non-uniformly saturated, frictionless, and moist adiabatic flow

摘要

Because of the discontinuity of the latent heat release in the thermodynamic equation in the transitional area between the unsaturated and saturated air, the condensation probability function (q/q s) k (q and q s are specific humidity and saturated specific humidity, respectively, k = 9) is introduced into the thermodynamic equation. Then, the ageostrophic diabatic ω equation, in which ▽ · Q um is the single forcing term, is derived in a non-uniformly saturated moist atmosphere. Qum includes the effects of both latent heat and relative humidity, and it is generated only in nearly saturated regions by the effect of the condensation probability function. To diagnose Qum, a rainfall case associated with the Meiyu front in the midlower reaches of the Yangtze River in China is numerically simulated using the Weather Research and Forecasting model. The results show that the divergence of Qum diagnoses the occurrence and evolution of rainfall better than those of dry Q vector and Qm in the lower troposphere do, and that ▽ · Qum is a better precursor for the future 6-hour precipitation.