Impact of All-Sky Microwave Radiance Assimilation of Megha-Tropiques SAPHIR Data on Short-Range Weather Forecasts

Accuracy of the ab initio state of the atmosphere is crucial for improvement in forecast skill of any Numerical Weather Prediction (NWP) model. The data deficiency over open ocean is tackled with the use of space-borne sensors such as satellites which provide data continuously at a high resolution spatially as well as temporally. Several studies have shown the positive impact of clear sky radiance data from different microwave sensors on the forecast accuracy. Cloud and precipitation-affected radiances from microwave satellite sensors when incorporated in the data assimilation system has a huge potential in further improving the accuracy. Megha-Tropiques is an Indian Space Research Organisation/Centre National d’Etudes Spatiales joint satellite mission for studying the water cycle and energy exchanges in the tropics. SAPHIR (Sounder for Atmospheric Profiling of Humidity in the Inter-tropics by Radiometry) is a six channel microwave sounder aboard Megha-Tropiques satellite. In this study, an attempt is being made to assimilate the all-sky radiance (clear sky and cloudy sky) from the microwave sounder present in SAPHIR by employing the multiple scattering radiative transfer model RTTOV-SCATT. To examine the importance of cloud-affected radiance data during the Indian Summer Monsoon, all-sky radiance simulation will be carried out for the month of July 2016 over the Indian subcontinent. The all-sky radiances from SAPHIR will be ingested into the WRF model using a Four-Dimensional Variational Assimilation(4D-Var) technique. The daily accumulated rainfall data simulated from the WRF model will be validated against the India Meteorological Department (IMD) gridded dataset and Tropical Rainfall Measuring Mission (TRMM) data to assess the impact of the assimilation. The effect of assimilation on winds and moisture over land and ocean regions will also be studied.

References:

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