Study on Sensitivity of Microphysics for the Simulation of Rainfall for the Month of May 2015 over Bangladesh using High Resolution WRF

Abstract

In the present study, the Advanced Research WRF (ARW) model v3.8.1 has been used to simulate the rainfall for the month of May 2015 all over Bangladesh. The initial and boundary conditions are drawn from the global operational analysis and forecast products of National Center for Environmental Prediction (NCEP-FNL) available at 1˚×1˚ resolution. The model was configured in nested domain with 18 and 6 km horizontal grid spacing with 100 × 96 and 103 × 127 grids respectively in the east-west north-south directions with 30 vertical levels. Time step of integration is set to 90 and 30 seconds for maintaining computational stability as the model uses third-order Runge-Kutta time integration scheme. In this research, six different microphysics schemes such as Lin et al., WSM6, Thomson, Morrison Double-Moment (M-2M), Stony Brook University (SBU), and WDM6 coupling with Kain-Fritsch (KF) cumulus parameterization scheme has been used to simulate the monthly total rainfall, monthly heavy rainfall, monthly rainy days and monthly heavy rainy days for the month of May 2015 all over Bangladesh. The outputs obtained by using different microphysics are compared with the observed outputs at 33 meteorological stations of BMD and Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN) output. Standard deviation of all observed, PERSIANN and model simulated parameters have been analyzed and compared. The maximum monthly observed rain of May 2015 at Sylhet is 752 mm but WSM6, M-2M and WDM6 schemes have simulated 831, 788 and 742 mm for day 1 prediction; WSM6, WDM6 and SBU-Lin schemes have simulated 757, 916 and 981 mm for day 2 prediction and WSM6 and WDM6 schemes have simulated 741 and 925 mm for day 3 prediction, respectively and all other MPs have simulated much higher rainfall at domain (D1). The WDM6, M-2M and Lin et al. schemes have simulated 744, 807 and 923 mm for day 1 prediction, WSM6 and WDM6 schemes are 714 and 877 mm for day 2 predictions and WSM6, SBU-Lin and Lin et al. schemes are 802 and 913 and 998 mm, respectively for day 3 prediction at domain (D2). WDM6 scheme gives the better performance of rainfall and rainy days all over the country.