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    Impact of PBL on the Simulation of Heavy Rainfall Events in the Monsoon Season Over Bangladesh Using WRF-ARW Model
    (Khulna University of Engineering & Technology (KUET), Khulna, Bangladesh., 2013-07) Islam, S. M. Rafiqul; Alam, Prof. Dr. Md. Mahbub
    In the present study the Advanced Research WRF (ARW) model version 3.2.1 has been used to simulate the heavy rainfall events of 27-29 July 2009, 15-16 August 2009, 26-27 June 2010 and 7-8 September 2011 over Bangladesh during monsoon season. To simulate the heavy rainfall events Lin et al. microphysics in combination with Kain-Fritsch (KF) cumulus parameterization (CP) scheme in a nested configuration has been used. In this study, six different planetary boundary layer (PBL) parameterizations schemes have been used to study the heavy rainfall events in monsoon season. The different PBL schemes have been considered are YSU, MYJ, QNSE, MYNN3, ACM2 and BouLac. The model domains consist of 9 km outer and 3 km inner domain horizontal resolution with 28 vertical sigma levels. NCEP FNL data have been used for the initial and lateral boundary condition. The WRF model has been run 72 hours for the heavy rainfall event 27-29 July 2009 and 48 hours for all other cases. Sensitivity experiments have been conducted with the WRF model to test the impact of Planetary Boundary Layer (PBL) schemes in capturing the extreme weather event. The rainfall, wind speed, relative humidity, accumulated upward heat flux, accumulated upward latent heat flux, downward long wave flux, outgoing long wave radiation, reflectivity, PBL thickness, kinematics and thermodynamic characteristics have been studied to identify the effect of PBL schemes on different heavy rainfall events. The simulated rainfall is maximum at the position where the outgoing long wave radiation, Accumulated upward heat flux and downward long wave flux are minimum. The simulated rainfall is maximum at the position where the reflectivity and the accumulated upward latent heat flux are also maximum. The simulated relative humidity at 850 hPa level is almost 98- 100% at different places over the country where maximum rainfall has been simulated. The simulated rainfall has been compared with observed rainfall of Bangladesh Meteorological Department (BMD) and TRMM 3B42RT rainfall. For the simulation of four heavy rainfall events with four initial conditions, the BouLac PBL scheme has given the better result. After BouLac PBL scheme, YSU and ACM2 have given the better result for the simulation of heavy rainfall events.
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    Study on Sensitivity of Microphysics for the Simulation of Rainfall for the Month of May 2015 over Bangladesh using High Resolution WRF
    (Khulna University of Engineering & Technology (KUET), Khulna, Bangladesh, 2019-03) Khan, Md. Salman; Alam, Prof. Dr. Md. Mahbub
    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.