Influences Of Sub-grid Convective Processes On Cloud Forecast In GRAPES Global Model

The purpose of the research is to improve the prediction of the hydrometeors watercontent, cloud fraction and grid precipitation by the Global/Regional Assimilation andPrediction System (GRAPES) global model at50km spatial resolution for the low latitudesand equatorial regions. This study adopts a new scheme that considering the impact of thissub-grid convective process by adding source-sink terms in the prediction equations of cloudwater/ice and cloud fraction. Distinct forecast results from the previous cloud scheme areobtained. The forecasts of cloud and precipitation in the low latitudes and equatorial regionshave been significantly improved after consideration of the effect of the sub-grid convectiveprocess. Moreover, compared with the observational data from the Clouds and the Earth’sRadiant Energy System (CERES) and CloudSat and Tropical Rainfall Measuring Mission(TRMM), it is confirmed that the forecasting capability of the GRAPES global model hasbeen promoted especially for the cloud and precipitation in the tropics, The proportion ofgrid-scale precipitation enhances grows from5%to25%. Further analysis reveals that theinfluence of the sub-scale convectiveprocess on gird-scale cloud and precipitation depends onthe distribution and intensity of updraft mass flux, which turns into larger from the newscheme, in the tropics, leading to notable increases of cloud and precipitation there. Inaddition, the maximum updraft mass flux resides in the450-650hPa layer, resulting inpronounced improvement in forecast of middle-level clouds than high clouds and low-levelclouds, and causes cloud top to rise while cloud bottom to drop downward in the vertical.