METHODS OF SHORT-TERM FORECASTING OF NONCONVECTIVE CLOUDS AND PRECIPITATION USING A MOISTURE TRANSFORMATION MODEL, WITH MICROPHYSICS PARAMETRIZATION. 1. MOISTURE TRANSFORMATION MODEL AND NONCONVECTIVE CLOUD FORECASTING

L. R. Dmitrieva-Arrago

A large-scale model of moisture transformation in the atmosphere is presented, consisting of the equations of continuity and of dew point deficit and liquid water content transfer. A method is suggested of the specification of liquid water content initial data. The model is run in the stereographic projection of the Northern Hemisphere with 75 × 75 and 150 × 150 km horizontal steps and 15 levels in the vertical direction. The model is designed to compute nonconvective clouds and precipitation. A method of subgrid cloud parametrization is developed. The total cloud amount computation error for 36-h forecast is within 2 points. The computed liquid water content corresponds to measured typical values for St and Sc clouds, to 0.2—0.4 g/m3, and integral water content corresponds to satellite radiometer data (to 1.4—1.5 kg/m2). For the model running, data on horizontal wind components and temperature are necessary. At present, the output data from the spectral model of the Hydrometeorological Center of Russia are used. Spatial distribution of clouds and liquid water content computed by the moisture transformation model is used in the technique of nonconvective cloud microphysical pro¬cess description and in a precipitation determination diagnostic method which are presented in the second part of the paper.

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