Evaluation of microwave radiances of GPM/GMI for the all-sky assimilation in RTTOV framework

Abstract. This study evaluates the all-sky GPM/GMI radiances towards assimilation in regional mesoscale model at 183 ± 7 GHz. The radiative transfer model (RTM) namely RTTOV-SCATT is used for the simulation of three tropical cyclones (hudhud, vardah and kyant respectively). Within the RTM, the performance of non-spherical Discrete Dipole Approximation (DDA) shapes (sector snowflake, 6-bullet rosette, block-column and thinplate) are evaluated. The input data used in RTTOV-SCATT includes vertical hydrometeor profiles, humidity and surface fluxes. In addition, the first guess simulations from Weather Research Forecast (WRF) model were executed at 15 km resolution using ERA-Interim reanalysis datasets. Results indicate that observed minus first guess (FG departures) are symmetric with DDA shapes. The normalized probability density function of FG departures shows large number of spatially correlated samples between clear-sky and poorly forecasted region. Quality control (QC) method was performed to eliminate large FG departures due to instrumental anomalies or poor forecast of clouds and precipitation. The goodness of fit test, h-statistics and skewness of observed and simulated distribution show optimum results for thinplate shape in all the convective events. We also tested the high resolution ERA-5 reanalysis datasets for the simulation of all-sky radiances using thinplate shape. Results illustrate a potential to integrate the GMI sensor data within a WRF data assimilation system.