Rainfall estimation of landfalling tropical cyclones over Indian coasts through satellite imagery

lkj & m".kdfVca/kh; pOokrksa ds rV ls Vdjkus dk lcls egRoiw.kZ izHkko ;g gksrk gS fd blls cgqr vf/kd o"kkZ gksrh gSA bl 'kks/k i= dk eq(; mn~ns'; izpkyukRed iwokZuqekudrkZvksa dks bu pOokrksa ds rV ls Vdjkus ds ckn izHkkfor {ks=ksa esa gksus okyh o"kkZ dh laHkkoukvksa dks n'kkZusa ds fy, dqN ekxZn;u ls ;g irk pyk gS fd m".kdfVca/kh; pOokr dh xfr ds izFke oRrikn esa vf/kdre o"kkZ gqbZ gS) mlds f}rh; oRrikn esa o"kkZ gqbZ gS vkSj pOokrksa ds ekxZ ds utnhdh {ks=ksa esa o"kkZ gqbZ gSA izR;sd pOokrksa ds fy, 24 ?kaVksa esa gqbZ o"kkZ dk leo"kkZ fo'ys"k.k djus ls irk pyk gS fd rwQku dsUnz ls 150 fd- eh- dh f=T;k esa gh lkekU;r% Hkkjh o"kkZ gksrh gS vkSj djhc 300 fd- eh- rd o"kkZ gksrh gS rFkk o"kkZ dh ek=k /khjs&/khjs de gksrh tkrh gSA o"kkZ gksus okys {ks= vDlj laoguh; es?kksa ls vkPNkfnr jgrs gS vkSj bl flLVe ds LFky izos'k ds iwoZ vkSj ckn esa ckny 'kh"kZ ds rkieku -80 ls -60 fMxzh lsfYl;l rd gksrs gSaA v/;;u fd, x, 14 ?kVukvksa esa ls 93 izfr'kr m".kdfVca/kh; pOokr gS) blesa ls 70 izfr'kr dk laogu ekxZ ds nk,i rjQ gqvk gSA laogu forj.k esa fo"kerk ds dkj.k gqbZ o"kkZ dh fo"kerk dh tkip djus ds fy, mixzg vojDr fp= vkidM+ksa ls es?k 'kh"kZ ds rkieku izkIr fd, x, gS ftls izkSDlh vkWQ LVakix duosD'ku ds :i esa fy;k x;k gSA bl v/;;u ls ;g irk Hkh irk pyk gS fd rhoz xfr ls c<+us okys m".kdfVca/kh; pOokrksa dh rqyuk esa /kheh xfr ls c<+us okys m".kdfVca/kh; pOokrksa ls Hkkjh o"kkZ gksrh gSA caxky dh (kkM+h esa fufeZr pOokr tks leqnz rV dks pOokrh rwQku rFkk izpaM pOokrh rwQku ds :i esa ikj fd, muls 0&10 ls- eh- rd dh lhek esa 71-4 izfr'kr o"kkZ) 11&20 ls- eh- dh lhek esa 22-8 izfr'kr o"kkZ vkSj 21&30 ls- eh- dh lhek esa 4-3 izfr'kr o"kkZ pOokrh rwQkuksa ds dsUnz ls 300 fd- eh- dh f=T;k okys {ks=ksa esa gqbZA vjc lkxj esa fufeZr m".kdfVca/kh; pOokrksa ls lkekU;r% 24 ?kaVksa esa 16&25 ls- eh- dh lhek esa yxHkx 70 izfr'kr o"kkZ gqbZ gSA ABSTRACT. One of the most significant impacts of landfalling tropical cyclones is caused by the copious rainfall associated with it. The main emphasis of present study is to provide some guidance to the operational forecasters for indicating the possible rainfall over the areas likely to be affected by the cyclones after landfall. Study of 14 past landfalling cyclones reveals that the maximum rainfall occurred in the first forward quadrant of tropical cyclone movement, followed by the second quadrant and the areas near the track of the cyclones. Isohyetal analysis of 24 hours rainfall for each cyclone reveals that occurrence of heavy rainfall is generally confined up to 150 kms radius from the storm centre and rainfall is found to generally extend up to 300 kms with gradual decrease in amount. The rainfall receiving areas are mostly covered with convective clouds with cloud top temperatures of -80 to -60 oC, prior to and after the landfall of the systems. In 93% of tropical cyclones out of the 14 cases studied, 70 % convection lay to the right of the track. To examine the rainfall asymmetry due to asymmetry in distribution of convection, cloud top temperatures derived from satellite infrared imagery data have been taken as the proxy of strong convection. It is also revealed in the study that the slow moving tropical cyclones cause heavy rain rather than fast moving tropical cyclones. The Bay of Bengal cyclones which crossed coast as cyclonic storm and very severe cyclonic storm caused 71.4% rainfall within the range 0- 10 cm, 22.8% rainfall in the range 11-20 cm and 4.3% rainfall within the range 21-30 cm in the area of radius of 300 kms from the centre of the cyclonic storms. For the Arabian Sea tropical cyclones, in general, about 70% rainfall occurred within the range 16-25 cm in 24 hours.