SHORT-RANGE PRECIPITATION FORECASTS USING ASSIMILATION OF SIMULATED SATELLITE WATER-VAPOR PROFILES AND COLUMN CLOUD LIQUID WATER AMOUNTS

These observing system simulation experiments investigate the assimila tion of satellite-observed water vapor and cloud liquid water data in the initialization of a limited-area primitive equations model with th e goal of improving short-range precipitation forecasts. The assimilat ion procedure presented includes two aspects: specification of an init ial cloud liquid water vertical distribution and diabatic initializati on. The satellite data is simulated for the next generation of polar-o rbiting satellite instruments, the Advanced Microwave Sounding Unit (A MSU) and the High-Resolution Infrared Sounder (HIRS), which are schedu led to be launched on the NOAA-K satellite in the mid-1990s. Based on cloud-top height and total column cloud liquid water amounts simulated for satellite data, a diagnostic method is used to specify an initial cloud water vertical distribution and to modify the initial moisture distribution in cloudy areas. Using a diabatic initialization procedur e, the associated latent heating profiles are directly assimilated int o the numerical model. The initial heating is estimated by time averag ing the latent heat release from convective and large-scale condensati on during the early forecast stage after insertion of satellite-observ ed temperature, water vapor, and cloud water information. The assimila tion of satellite-observed moisture and cloud water, together with thr ee-mode diabatic initialization, significantly alleviates the model pr ecipitation spinup problem, especially in the first 3 h of the forecas t. Experimental forecasts indicate that the impact of satellite-observ ed temperature and water vapor profiles and cloud water alone in the i nitialization procedure shortens the spinup time for precipitation rat es by 1-2 h and for regeneration of the areal coverage by 3 h. The dia batic initialization further reduces the precipitation spinup time (co mpared to adiabatic initialization) by 1 h.