Thunderstorm is a mesoscale system (from a km to below thousands of km and sustaining less than one hour). Two pre-monsoon thunderstorms events are analyzed in this study which are named as event-1 (0030-0150 UTC of 19 April 2018 over Chattogram) and event-2 (0600-1000 UTC of 4 May 2018 over Dhaka). To predict these events Mean Convective Available Potential Energy (mCAPE), Mean Convective Inhibition Energy (mCINE), K Index (KI), Total totals Index (TTI), wind distribution, and relative humidity (RH) are investigated.The model simulated mCAPE and mCINE values, 18 hours before the events, are found greater than 1700 J/Kg and less than 100 J/Kg respectively which satisfies the conditions for thunderstorms to occur.The KI values are close to 400C and TTI values are greater or equal to 450C for both events. The wind patterns and the high value of mid –tropospheric RH also favors the formation of severe thunderstorm. Dhaka Univ. J. Sci. 67(2): 151-156, 2019 (July)

Heat waves (HWs) are an extreme temperature condition that has a direct impact on human lives. In recent years, a large number ofpeople have died all over the world due to hot weather. The purpose of this study is to predict HWs accurately to mitigate the casualtiescaused by them. Two HW events are selected for this study (Event-1: 0000 UTC of 18 May to 0000 UTC of 25 May 2015, Event-2:0000 UTC of 05 April to 2100 UTC of 08 April 2015). At first, sensitivity tests have been done using different combinations ofphysics schemes. Sensitivity of Planetary boundary layer (PBL) and surface layer (SL) schemes combinations (YSU-Revised MM5,YSU-MM5, MYJ-Eta, and ACM2-Revised MM5) and land surface models (RUC, Noah, Noah-MP, and CLM4) are investigated topredict Comfort Index (CI), which is identified by using Physiological Equivalent Temperature (PET). To simulate PET, the primarymeteorological variables 2-m air temperature (T2), 2-m relative humidity (rh2), mean radiant temperature (TMRT), wind speed at 10m (ws10), and cloud cover data have been used. These parameters were simulated by the WRF model using both single and nesteddomains. The experiments found that the combination of the YSU-MM5 scheme and the Noah land surface model predicted theWRF simulated variables very well. The study also found that the CI exists between the slight heat stress to extreme heat stress andthe maximum PET values were found to be 47.6 ºC and 48.5 ºC for Rajshahi and Khulna event respectively. Dhaka Univ. J. Sci. 70(1): 70-78, 2022 (January)

Metal halide perovskites that do not contain lead are non-toxic and offer a wide range of uses in low-cost photovoltaic and optoelectronic systems. In this report, density functional theory is used to explore the influence of pressure (0-150 GPa) on the structural, electronic and optical characteristics of RbSrCl3 perovskite metal halide. At 0 GPa, RbSrCl3 was found to be an indirect wide-bandgap semiconductor. Under pressure, the electronic band gap transforms to visible range direct band gap which is suitable for optoelectronic devices. Higher absorption for RbSrCl3 was found in the ultraviolet region under the influence of different pressures. As the pressure on the halide perovskite increased, absorption peak is shifted to higher energy range. The optical conductivity, reflectivity and extinction coefficient were significantly changed due to induced pressures. The results suggest that under uniform pressure RbSrCl3 can be used in optoelectronic applications.

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