Simulation of a heavy rainfall event of 11 June 2007 over Chittagong, Bangladesh using MM5 model

Abstract

bl 'kks/k i= esa ikapoh ih<+h ¼tsujs’ku½ ds ih- ,l- ;w-@,u- lh- ,- vkj- eslksLdsy ekWMy 5   ¼,e- ,e- 5½ dk mi;ksx djrs gq, caxykns’k ds fpV~Vxkao esa fnukad 11 twu] 2007 dks gqbZ Hkkjh o"kkZ dh ?kVuk dks le>kus dk iz;kl fd;k x;k gSA ;g vlkekU; o"kkZ dh ?kVuk fpV~Vxkao {ks= esa gqbZ vkSj ml fnu 24 ?kaVs dh vof/k esa 425 fe- eh- o"kkZ vfHkysf[kr dh xbZA blds ifj.kkeLo:i vkdfLed ck<+ vk tkus vkSj Hkw&L[kyu gksus ls tku&eky dk Hkkjh uqdlku gqvkA e/; vof/k iwokZuqeku ¼,e- vkj- ,Q-½ xzgh; ifjlhek Lrj ¼ih- ih- ,y-½ ;kstuk ds lkFk ,UFkhl-dqvks ¼vFkkZr ,- ds-½ diklh izkpyhdj.k ;kstuk ¼lh- ih- ,l-½ dk mi;ksx djrs gq, f=&Lrjh; {ks=ksa esa 45] 15] 5 fd-eh- ds {kSfrt foHksnu esa bl ,e- ,e- 5 ekWMy dks pyk;k x;kA ,e- ,e- 5 ls izkIr  fd, ifj.kkeksa ls irk pyk gS fd fpV~Vxkao ds LFkkuh; {ks= esa Hkkjh o"kkZ dk dkj.k o`gRr iSekus ij lfØ; ekWulwu iz.kkyh ds lkFk eslksLdsy ds rhoz laoguh; ifØ;kvksa dk ijLij izHkko FkkA fo’ys"k.k ls irk pyk gS fd fpV~Vxkao ds Åij fufeZr laoguh; lsy ¼es?kiqat½ vR;kf/kd l?ku ijarq vYidkfyd Fks vkSj mlds fy, caxky dh [kkM+h ls vko’;d ueh feyh FkhA bl ,e- ,e- 5 ekWMy esa diklh izkpyhdj.k dk lqxzkfgrk ijh{k.k Hkh fd;k x;k gSA bu ifj.kkeksa ls irk pyrk gS fd izsf{kr Vh- vkj- ,e- ,e- o"kkZ dh rqyuk esa MCY;w- vkj- ,Q- ih- ch- ,y- lw=hdj.k ls ,- ds- lh- ih- ,l- }kjk bl ekWMy esa fpV~Vxkao esa gqbZ o"kkZ dh vf/kd ek=k dk vkdyu fd;k x;k gS vkSj xsy] ds- ,Q-] ch- ,e- }kjk ds- ,Q- 2 ds diklh es?k izkpyhdj.k ;kstukvksa }kjk o"kkZ dh de ek=k dk vkdyu fd;k x;k gS rFkk ch- ,e- Mh- vkj- ,u- lh- dh rqyuk esa laiw.kZ lh- ih- ,l- dk de vkdyu fd;k x;k gSA varr% ,e- vkj- vkQ- ih- ch- ,y- ds lkFk ,UFkhl dqvks diklh ;kstuk dks caxykns’k esa gqbZ o"kkZ ds vkdyu ds fy, csgrj ik;k x;k gSA bl ekWMy ds dk;Zfu"iknu dk vkdyu vkSlr leqnz ry nkc] Åijh ,oa fupys Lrj esa ok;q ifjlapj.k] iou vi:i.k] lkisf{kd Hkzfeyrk] vfHklj.k] ueh ,oa o"kkZ tSls iwokZuqeku ds fHkUu&fHkUu izkpyks dh tkap djds fd;k x;k gSA bu ifj.kkeksa ls irk pyrk gS fd ,e- ,e- 5 ekWMy dks NksV&NksVs {ks=ksa] {kSfrt foHksnu ,oa diklh izkpyhdj.k ;kstuvksa ds lgh feJ.k ls Hkkjh o"kkZ dh ?kVuk vkSj blls lacaf/kr flukWfIVd fo’ks"krkvksa dh lgh tkudkjh nh tk ldrh gS fQj Hkh o"kkZ ds iSVuZ ds laca/k esa dqN iwokZxzg gSA

 The present study attempts to simulate a heavy rainfall event that occurred on 11 June 2007 over Chittagong, Bangladesh using the Fifth-Generation PSU/NCAR Mesoscale Model (MM5). This extraordinary rainfall event was localized over Chittagong region and recorded 425 mm of rainfall within a span of 24 hrs on that eventful day. The event resulted in large human and economic losses due to flash flood and land slide. The MM5 model was run on triple-nested domains at 45, 15, 5 km horizontal resolution using Anthes-Kuo (i.e., AK) cumulus parameterization scheme (CPS) with medium range forecast (MRF) planetary boundary layer (PBL) scheme. The results obtained through MM5 suggest that the highly localized heavy rain over Chittagong was the result of an interaction of the mesoscale severe convective processes with the large scale active monsoon system. The analysis shows that the convective cells formed over Chittagong were very intense but short-lived and required moisture have been supplied from the Bay of Bengal. A sensitivity test of cumulus parameterizations in MM5 model has also been conducted. The results show that the model simulated rainfall amount over Chittagong has been overestimated by AK CPS with MRF PBL formulation and underestimated by Grell, KF, BM and KF2 cumulus parameterization schemes compared to the observed TRMM rainfall and all CPS are underestimated as compared with BMD RNG. Finally, the Anthes-Kuo cumulus scheme with MRF PBL has been found to perform better in estimating rainfall over Bangladesh. The model performance was evaluated by examining the different predicted parameters like mean sea level pressure, upper and lower level circulations, wind shear, relative vorticity, convergence, moisture and rainfall. The results indicate that the MM5 model with the right combination of the nesting domain, horizontal resolution and cumulus parameterization schemes was able to simulate the heavy rainfall event, and associated synoptic features reasonably well, though there are some biases in the rainfall pattern.