Numerical study of western disturbances over western Himalayas using mesoscale model

Hkkjrh; {ks= esa ’khr _rq ds nkSjku if’peh fo{kksHkksa ¼MCY;w-Mh-½ dh egRoiw.kZ fo’ks"krkvksa dks izfr:fir djus ds fy, isu LVsV ;wfuoflZVh&us’kuy lsUVj Qksj ,V~eksLQsfjd fjlpZ ¼ih-,l-;w-&,u-lh-,-vkj-½ la;qDr jkT; vejhdk ds xSj ty LFkSfrd :ikUrj ds rkSj ij eslksLdsy ekWMy ¼,e- ,e- 5½ dk mi;ksx fd;k x;k gSA bl v/;;u esa nks xzgh; ifjlhek Lrj i)fr;ksa uker%&CySdknj ,oa gkSax&iSu rFkk pkj laogu izkpyhdj.k i)fr;ksa uker% dqvks] xzsy] dSufÝz’k ,oa csV~l&feYyj ds 60 fd- eh- ds {kSfrt foHksnu ekWMy dk mi;ksx djds vkB lqxzkfgrk iz;ksx fd, x, gaSA blesa {kSfrt foHksnu ekWMy rFkk LFkykÑfr ds egRo ds nks dkjdksa&30 fd-eh-] 60 fd-eh- ,oa 90 fd- eh- ds {kSfrt foHksnu ekWMy ftlesa ,d fLFkfr esa LFkykÑfr ij fopkj ugha fd;k x;k gS rFkk nwljh esa lkekU; LFkykÑfr ij fopkj fd;k x;k gS] ds vk/kkj ij N% iz;ksx djds v/;;u fd;k x;k gSA bl v/;;u ds fy, nks lfØ; if’peh fo{kksHkksa dk p;u fd;k x;k gS ftlds dkj.k if’peh fgeky; {ks= esa Hkkjh o`f"V gqbZA izFke v/;;u ds fy, 18 tuojh ls 21 tuojh] 1997 rd dh vof/k ds nkSjku ds if’peh fo{kksHk dk p;u fd;k x;k gS rFkk nwljs iz;ksx ds fy, 20 tuojh ls 25 tuojh] 1999 dh vof/k ds nkSjku ds if’peh fo{kksHk dk p;u fd;k x;k gSA blesa vkjafHkd rFkk lhekar fLFkfr;ksa ds fy, us’kuy lsUVj QkWj bu~okbjWuesUV fizMhD’ku&us’kuy lsUVj QkWj ,V~eksLQsfjd fjlpZ ¼,u- lh- b- ih-&,u- lh- , - vkj-½ la;qDr jkT; vejhdk }kjk iqufoZ’ysf"kr vkaadM+ksa dk mi;ksx fd;k x;k gSA bl v/;;u ls ;g irk pyk gS fd gkSax&iSu vkSj csV~l feYyj dh Øe’k% xzgh; ifjlhek Lrj rFkk es?k laogu izkpyhdj.k i)fr ds la;kstu dk izn’kZu mi;ksx dh xbZ vU; la;kstu i)fr;ksa ds rqyuk esa lcls vPNk jgk gSA vkn’kZ HkkSfrdh ¼ekWMy fQftDl½ vU; la;kstu i)fr;ksa dh rqyuk esa bl la;kstu ds }kjk leqnz ry dk nkc T;knk lgh izfr:fir djus esa l{ke jgh gSA blds vykok LFkykÑfr jfgr {ks= esa if’peh fo{kksHk dk izfr:i.k lkekU; LFkykÑfr esa izfr:fIkr if’peh fo{kksHk dh rqyuk esa de o"kkZ dh ek=k dks n’kkZrk gSA tc blesa lkekU; LFkykÑfr dks ’kkfey fd;k x;k rks fgeky; {ks= ds vkl&ikl Hkkjh o"kkZ gqbZA o"kkZ ds {ks=ksa ds ,dhÑr ekWMy lR;kfir fo’ys"k.k ds vuq:Ik ik, x, gaSA o"kkZ {ks=ksa ds lqxzkfgrk v/;;u ls irk pyk gS fd NksVs izHkko& {ks= ¼30 fd-eh-½ ds izfr:fir ekWMy vPNs ifj.kke nsrs gSaA ” A non-hydrostatic version of the Penn State University - National Center for Atmospheric Research (PSU-NCAR), US, Mesoscale Model (MM5) is used to simulate the characteristic features of the Western Disturbances (WDs) occurred over the Indian region during winter. In the present study sensitivity eight experiments are carried out by using two planetary boundary layer schemes, viz., Blackadar and Hong-Pan, and four convection parameterization schemes, viz., Kuo, Grell, Kain-Fristch and Betts-Miller, with 60 km horizontal model resolution. And also the role of horizontal model resolution and topography is studied by carrying out six experiments based on two factors: horizontal model resolution of 30 km, 60 km and 90 km with assumed no topography and normal topography. For this study two active WDs are chosen which yielded extensive precipitation over western Himalayas. WD from 18 to 21 January 1997 is chosen for study one and WD from 20 to 25 January 1999 is chosen for experiment two. National Center for Environmental Prediction – National Center for Atmospheric Research (NCEP-NCAR), US, reanalyzed data is used for initial and boundary conditions. It is found that the performance of combination of the Hong-Pan and Betts-Miller as planetary boundary layer and cloud convection parameterization schemes respectively is best compared to the other combinations of schemes used in this study. The model physics could able to simulate sea level pressure better with this combination as compared to the combinations with other schemes. Further, WD simulations with assumed no topography shows lesser amount of precipitation compared to WD simulations with normal topography. When normal topography is included, intense localized of precipitation was observed along the Himalayan range. Model integrations of precipitation fields are found close to the corresponding verification analysis. Sensitivity studies of precipitation field shows that finer domain (30 km) of the model simulation gives better results.