A study on high resolution mesoscale modeling systems for simulation of tropical cyclones over the Bay of Bengal

Abstract

LFky izos’k djus okyk m".kdfVca/kh; pØokr ¼Vh- lh-½ izk—frd vkinkvksa esa ls ,d gS ftldh otg ls cgqr rst gok,¡ pyrh gS] ewlyk/kkj o"kkZ gksrh gS] blds LFky izos’k ds LFkku ls dbZ fdyksehVj rd ck<+ vk tkrh gS vkSj rwQkuh leqnzh rjaxsa ehyksa rd rVorhZ {ks=ksa dks izHkkfor djrh gSa ftlds QyLo:i tkusa pyh tkrh gSa vkSj laifRr dh {kfr gksrh gSA ;g vkink caxky dh [kkM+h ¼ch-vks-ch-½ ls lVs {ks=ksa esa vf/kd vkrh gSA blfy, Hkkjr ekSle foKku foHkkx ¼vkbZ- ,e- Mh-½ us m".kdfVca/kh; pØokr dk csgrj iwokZuqeku nsus ds fy, caxky dh [kkM+h esa cuus okys m".kdfVca/kh; pØokr dh mRifRr] mldh rhozrk vkSj jpuk dh foLr`r tkudkjh izkIr djus ds fy, ‘QksjdkLV fMekWUlVsª’ku izkstsDV ¼,Q-Mh-ih-½ vkWQ ysaMQkWfyax lkbZdyksal’ uked ,d QhYM ifj;kstuk vkjaHk dh gSA LFky izos’k djus ds fy, m".kdfVca/kh; pØokrksa us vuq:i.k gsrq ,Q-Mh-ih- ¼2008&2011½ ds vkjafHkd pj.k esa vR;k/kqfud eslksLdsy ekWMqyu iz.kkfy;ksa tSls & ,Mokal fjlpZ osnj fjlpZ ,.M QkWjdkfLVx ¼,- vkj- MCY;w-½] MCY;w- vkj- ,Q- ¼,u- ,e- ,e-½ dk vnzoLFkSfrd eslksLdsy ekWMy rFkk gjhdsu  osnj fjlpZ ,.M QkWjdkfLVx ¼,p- MCY;w- vkj- ,Q-½ vkfn ds O;kid dk;Zfu"iknu  dks izLrqr fd;k x;k gSA fHkUu & fHkUu ekWMqyu iz.kkfy;ksa dk ijLij rqyuk djuk bl 'kks/k dk vk’k; ugha gSA bl 'kks/k i= esa N% m".kdfVca/kh; pØokrksa uker% jf’e ¼2008½] dSeqd ¼2008½] fu’kk ¼2008½] fxjh ¼2010½] ty ¼2010½ vkSj Fkk.ksa ¼2011½ dks fy;k x;k gSA ;|fi bl 'kks/k i= esa m".kdfVca/kh; pØokr ds fHkUu & fHkUu igyqvksa tSls & VSªd] rhozrk] ljapuk vkSj o"kkZ ds  ckjs esa foLr`r v/;;u fd;k x;k gSA bl 'kks/k i= esa VSªd ,oa rhozrk ds iwokZuqeku rFkk blls lacaf/kr =qfV;ksa ds Åij eq[; :i ls tksj fn;k x;k gSA

blds ifj.kke ls ;g irk pyk gS fd mPp foHksnu eslksLdsy ekWMqyu iz.kkfy;k¡ 72 ?kaVksa rd m".kdfVca/kh; pØokrksa ds iwokZuqeku nsus ds fy, csgrj ekxZn’kZu nsrh gSA gkyk¡fd tc bu ekWMyksa dh 'kq:vkr vifj"—r fo;kstu HkweaMyh; fo’ys"k.k ,oa iwokZuqeku {ks=ksa ds lkFk dh xbZ rks buesa VSªd ,oa rhozrk =qfV;k¡ vis{kk—r vf/kd ikbZ xbZ gaSA  ekWMy ds vkjafHkd voLFkkvksa esa vfrfjDr LFkkuh; izs{ks.kksa dks lekfgr djrs gq, bu =qfV;ksa dks lkFkZd :i ls de fd;k tk ldrk gSA VSªd iwokZuqeku =qfV;ksa dh x.kuk Hkkjr ekSle foHkkx ds csLV VSªd izs{k.kksa ds vk/kkj ij dh xbZ gSA ,- vkj- MCY;w- iz.kkyh esa Lokaxhdj.k iz;ksx ds fcuk iwokZuqeku =qfV;k¡ 138] 135 ,oa 182 fd- eh- ikbZ xbZ gSaA ,Q-Mh-ih-vof/k ds nkSjku lHkh miyC/k izs{k.kksa dks ekWMy dh vkjafHkd voLFkk esa lfEefyr fd, tkus ij =qfV;ksa esa 72] 99 ,oa 126 fd-eh- dh deh Øe’k% 24] 48 ,oa 72osa ?kaVs esa ikbZ xbZ gS vkSj blls yxHkx 47 izfr’kr dk lq/kkj ns[kk x;k gSA ,u-,e-,e- ekWMy ds ekeys esa vLokaxhdj.k iz;ksx dh rqyuk esa vk¡dM+ksa ds Lokaxhdj.k iz;ksx ls vkSlr VSªd =qfV;k¡ ¼30 mi fLFkfr;ksa ij vk/kkfjr½ esa yxHkx 32 izfr’kr] 22 izfr’kr] 23 izfr’kr] 28 izfr’kr] 24 izfr’kr ,oa 16 izfr’kr dk lq/kkj Øe’k% 00] 24] 48] 72] 96 ,oa 120 ?kaVs ij gqvk gSA ,p-MCY;w-vkj-,Q- ekWMy dh vkjafHkd fLFkfr ,oa ljapuk esa egRoiw.kZ :i ls lq/kkj bl fy, gqvk D;ksafd blds oksjVsDl&fjyksds’ku ,oa vkjafHkd izfØ;kvksa esa lq/kkj gqvk gSA blfy, blls m".kdfVca/kh; pØokr fxjh ds rhoz xfr ls vkxs c<+us dk vkxkeh ?kaVs esa iwokZuqeku fn;k tk ldkA

Landfalling tropical cyclone (TC) is one of the natural disasters producing extremely strong winds, torrential rains, floods influencing many kilometers from the point of landfall and storm surges that overwhelm miles of shores resulting loss of lives, and damages to properties. This disaster is higher in the regions covering Bay of Bengal (BoB). Therefore, the India Meteorological Department (IMD) initiated a field project, “Forecast Demonstration Project (FDP) of landfalling cyclones” over the BoB to acquire detailed understanding of genesis, intensity, and structure evolution of TCs so as for better TC forecasting. A comprehensive performance of state-of-the-art mesoscale modeling systems such as Advanced Research Weather Research and Forecasting (ARW), non-hydrostatic mesoscale model of WRF (NMM) and Hurricane Weather Research and Forecasting (HWRF) etc for the simulation of landfalling TCs during pilot phase of FDP (2008-2011) is presented. The study is not meant for the inter-comparison of different modeling systems. In the present study, six TCs namely Rashmi (2008), KhaiMuk (2008), Nisha (2008), Giri (2010), Jal (2010) and Thane (2011) are considered. Though different aspects of the TC such as track, intensity, structure and rainfall are studied in detail, this paper is mainly emphasized on the track and intensity prediction and associated errors.

Results indicates that the high resolution mesoscale modeling systems provide better guidance for TC forecast up to 72 hours. However, the track and intensity error is relatively more when these models are initialized with coarser resolution global analyses and forecast fields. This error can be significantly reduced with the assimilation of additional regional observations into model initial conditions. The track forecast errors are calculated with respect to IMD best track observations. In case of ARW system, the forecast errors are 138, 135 and 182 km from no-assimilation experiment. The assimilation of all available observations during FDP period into model initial condition decreases the errors 72, 99 and 126 km at 24, 48 and 72 hour, respectively with an improvement of about 47%. In case of NMM model, the mean (based on 30 sub-cases) track errors are improved by about 32%, 22%, 23%, 28%, 24% and 16% at 00, 24, 48, 72, 96 and 120 hrs, respectively with data assimilation experiments compared to no-assimilation experiment. The HWRF model improved the initial position and structure significantly because of its improved vortex-relocation and initialization procedures and hence captures the rapid intensification of the TC Giri in the subsequent forecast hour.