Assessing the Forecast Impact of a Geostationary Microwave Sounder using Regional and Global OSSEs

Forecast observing system simulation experiments (OSSEs) are conducted to assess the potential impact of geostationary microwave (GeoMW) sounder observations on numerical weather prediction forecasts. A regional OSSE is conducted using a tropical cyclone (TC) case that is very similar to hurricane Harvey (2017), as hurricanes are among the most devastating of weather-related natural disasters, and hurricane intensity continues to pose a significant challenge for numerical weather prediction. A global OSSE is conducted to assess the potential impact of a single GeoMW sounder centered over the continental United States versus two sounders positioned at the current locations of the National Oceanic and Atmospheric Administration Geostationary Operational Environmental Satellites (GOES) East and West. It is found that assimilation of GeoMW soundings result in better characterization of the TC environment, especially before and during intensification, which leads to significant improvements in forecasts of TC track and intensity. TC vertical structure (warm core thermal perturbation and horizontal wind distribution) is also substantially improved, as are the surface wind and precipitation extremes. In the global OSSE, assimilation of GeoMW soundings leads to slight improvement globally and significant improvement regionally, with regional impact equal to or greater than nearly all other observation types.

Recent advances in observational support from space-based systems for tropical cyclones

fiNys pkj n’kdksa ls m".kdfVca/kh; pØokrksa ¼Vh-lh-½ ds egRoiw.kZ izs{k.k miyC/k djkus esa ekSle foKkfud mixzgksa dh {kerkvksa ls lHkh ifjfpr gSA Hkw&LFkSfrd ekSle foKkfud mixzgksa ls izkIr n`’;] vojDr vkSj ty ok"i pSuyksa ls i`Foh ds es?kkPNknu ds yxkrkj izkIr gksus okys fp= vkSj bu vk¡dM+ksa ls ek=kRed mRiknksa dks rS;kj djus dh {kerk lcls egRoiw.kZ gSA ekSle foKkfud mixzg v/;;u lgdkjh laLFkku ¼lh-vkbZ-,e-,l-,l-½ foLdkasflu ;wfuoflZVh] ;w-,l-,- esa fiNys dqN o"kksZa esa fd, x, vuqla/kku ,oa fodkl iz;klksa ls m".kdfVca/kh; pØokrksa ds Lopkfyr fo’ys"k.k ds fy, ,d mUur M~oksjd rduhd ¼,-Mh-Vh-½ dk fodkl fd;k x;k gSA mRrjh vVykafVd vkSj dSfjfc;u lkxj esa vkus okys pØokrksa ds fo’ys"k.k ds fy, bl rduhd dk izpkyukRed mi;ksx fd;k tk jgk gSA tcfd Hkkjrh; leqnzksa esa ijEijkxr M~oksjd rduhd ¼Mh-Vh-½ csgrj dk;Z djrh gS rFkkfi gekjs {ks= esa bl le; izpkyukRed vk/kkj ij ,-Mh-,- dk mi;ksx bruk dkjxj ugha gSA lh-vkbZ-,e-,l-,l- esa fiNys dqN o"kksaZ esa vuqla/kku ,oa fodkl iz;klksa ls mixzg ds vk¡dM+ksa ls izkIr fd, x, ek=kRed mRiknksa esa Hkh dkQh lq/kkj gqvk gSA bu mRiknksa esa fuf’pr :i esa m".kdfVca/kh; pØokrksa ds fo’ys"k.k esa lq/kkj vk;k gS vkSj ;s m".kdfVca/kh; pØokrksa dh Hkkoh xfr fn’kk dk iwokZuqeku djus ds fy, egRoiw.kZ lwpuk miyC/k djkrs gaSA Hkkjrh; mixzgksa ds vk¡dM+ksa ls orZeku esa izpkyukRed mRiknksa dh xq.koRrk midj.kksa ds vifj"—r foHksnu ij vk/kkfjr gSA vxys o"kZ ¼2013½ ls bulSV Ja[kyk ds u, mixzg ls vf/kd csgrj xq.koRrk ds vk¡dM+sa miyC/k gksus ls mRiknksa dh xq.koRrk esa vkSj vf/kd lq/kkj vkus dh vPNh laHkkouk gSA lw{e rajx vk/kkfjr midj.kksa ls izkIr vk¡dMsa+ Hkh m".kdfVca/kh; pØokr ds fo’ys"k.k ds fy, vfrfjDr mi;ksxh lwpuk miyC/k djkrs gSaA Åijh {kksHkeaMy esa m".k dksj folaxfr m".kdfVca/kh; pØokr dh rhozrk dk mi;ksxh lwpd gSA Capabilities of meteorological satellites to provide vital observations on Tropical Cyclones (TC) are well known since more than last four decades. Most important are the frequent pictures of earth’s cloud cover in the visible, IR and water vapour channels obtained from Geostationary meteorological satellites together with the capability of generating a number of quantitative products from these data. R&D efforts of last several years at the Cooperative Institute of Meteorological Satellite Studies (CIMSS), Wisconsin University, USA have culminated into development of an Advanced Dvorak’s Technique (ADT) for automatic analysis of Tropical Cyclones. It is in operational use for analysis of North Atlantic and Caribbean Sea cyclones. It has been used on experimental basis at Satellite Meteorology Center, IMD while the conventional Dvorak Technique (DT) works well over the Indian seas, experience of using ADT does not permit at present its use on operational basis over our region. R&D efforts of last several years at CIMSS have also resulted in lot of improvements in the Quantitative products derived from the satellite data. These products have certainly improved the analysis of TC and have provided useful information for predicting the future intensity/movement of TCs. Quality of currently operational products from Indian satellite data is limited by the coarser resolution of the instruments. With the availability of much better quality of data from the new satellite of INSAT series from year (2013) onward there is a good possibility of making further improvements in the quality of products. Data obtained from microwave based instruments also provides useful additional information for TC analysis. The warm core anomaly in the upper troposphere is a useful indicator of the TC intensity.

Some structural characteristics of pre-monsoon depression in the Bay of Bengal

During the period 6 to 16 May. 1995. three deep depressions formed one after another over west Bay of Bengal and moved from south to north. In this paper, structural characteristics of these systems are investigated from the distribution of thermal and thermodynamical field observed around the depression center utilising daily Rs/Rw and other available coastal observations during the period, Major findings of the study are: (i) The depressions have low level cold core and middle and upper tropospheric warm core. (ii) Thermal and moisture fields tilt north ward with height but vertical tilt of contour height is .not uniform at all levels, (iii) During intensification of the system significant increase in temperature and moisutre occurs above 700 hPa and significant fall of contour height occurs below 300 hPa.

Deep Eye Clouds Observed in Tropical Cyclone Trami (2018) during T-PARCII Dropsonde Observations

The sporadic formation of short-lived convective clouds in the eye of Tropical Cyclone (TC) Trami (2018) is investigated using dropsonde data and simulation results from a coupled atmosphere–ocean model. According to the satellite data, top height of the convective clouds exceeds 9 km above mean sea level, considerably taller than that of typical hub clouds (2–3 km). These clouds are located 10–30 km away from the TC center. Hence, these convective clouds are called deep eye clouds (DECs) in this study. The dropsonde data reveal increase in relative humidity in the eye region during the formation of DECs. Short-lived convective clouds are simulated up to the middle troposphere in the eye region in the coupled model. Investigation of thermodynamic conditions shows a weakened low-level warm core and associated favorable conditions for convection in the eye region during the formation of DECs. DECs are formed after the weakening and outward displacement of convective heating within the eyewall. To elucidate the influence of the changes in convective heating within the eyewall on the formation of DECs, we calculate secondary circulation and associated adiabatic warming induced by convective heating within the eyewall using the Sawyer–Eliassen equation. In the eye region, weakenings of subsidence and associated vertical potential temperature advection are observed as DECs are formed. This suggests that the weakening and outward displacement of convective heating within the eyewall create favorable conditions for the sporadic formation of DECs.

On forecasting tracks of tropical disturbances using ATOVS data over Bay of Bengal

lkj &,d m".kdfVca/kh; vonkc ds thou pØ ds vkadMs+ rFkk nks m".kdfVca/kh; pØokrh rwQkuksa ds o"kZ 2002&03 dh vof/k ds vkadMs+ mPp Vh- vks- oh- ,l- ¼,- Vh- vks- oh- ,l-½ /kzqod{kh; mixzgksa ,u- vks- ,- , 15 rFkk 16] ftuesa mPp lw{e rjaxh; ifjKkiu bdkbZ ¼,- ,e- ,l- ;w½ yxh gqbZ gaS ls izkIr fd, x, gSa ftudk fo’ys"k.k bu rwQkuksa ds ekxZ dk iwokZuqeku djus ds fy, fd;k x;k gSA bu ekSle fo{kksHkksa ds 700&400 gsDVkikLdy ¼gs-ik-½ Lrj esa e/; {kksHkeaMyh; m".krk e/; Lrjh ckfgokZg ds dkj.k gksrh gS tks rwQku ds 200&700 fd-eh- vkxs rd foLrkfjr gksrh gS rFkk fo{kksHkksa dh xfr’khyrk dk djhc 6 ls 24 ?kaVs igys iwokZuqeku djus esa iwoZ ladsrd dk dk;Z djrh gSA ;g fo{kksHk yxHkx mlh v{k dks vuqxeu djrk gS tks e/; {kksHkeaMy esa foLrkfjr ¼vkxs c<s+ gq,½ ftg~okdkj m".k {ks= dks dsUnz ls tksM+rk gSA e/;e rhozrk okys nks HkweaMyh; pØokrksa dh fLFkfr esa tc 7º ls 13º lsfYl;l rkieku dk m"edksj Åijh {kksHkeaMyh; Lrj ¼250&200 gs-ik-½ ds djhc dsafnzr jgk ml le; vonkc dh fLFkfr esa fdlh fo’ks"k m".krk dk irk ugha pyk gSA Advanced TOVS (ATOVS), comprising the Advanced Microwave Sounding Unit (AMSU), data obtained from polar orbiting satellites NOAA 15 and 16 during the life cycle of a tropical depression and two tropical cyclonic storms during 2002-03 have been analysed to predict the track of these disturbances. The mid-tropospheric warming due to altostratus outflow from these weather disturbances in the layer 700 – 400 hPa which protrudes about 200 -700 km ahead the storm acts as a pre-cursor to predict the movement of the disturbances with a lead time of about 6 to 24 hours. The disturbance almost follows the axis connecting the centre with the warm tongue that protrudes ahead of the disturbance in the mid-troposphere. While warm core of 7 to 13° C is centered around the upper tropospheric level (250 – 200 hPa) in the case the two moderate intensity tropical cyclones, no significant warmness could be seen in the depression stage.

The evaluation of Kain-Fritsch scheme in tropical cyclone simulation

lkj & bl v/;;u esa 25&30 vDrwcj 1999 rd dh vof/k esa mM+hlk esa vk, egkpØokrksa ds ewY;kadu dk izfr:i.k djus ds fy, dSu fÝ’k ds diklh izkpyhdj.k ;kstuk ds lkFk ,u- lh- ,- vkj- ,e- ,e- 5 dk mi;ksx fd;k x;k gSA 25 vDrwcj 1999 ds 0000 ;w Vh lh ij 90] 30 vkSj 10 fd-eh- ds f}iFkh vk/kkfjr {kSfrt iz{ks=ksa ¼Mksesu½ okys ,u- lh- ,- vkj- ,e- ,e- 5 dks 5 fnu dh vof/k ds fy, lesfdr fd;k x;k gSA bl v/;;u ds fy, izkjfEHkd vkSj ifjlhek dh fLFkfr;ksa dks ,d va’k ds varjky ij miyC/k gq, ,u- lh- bZ- ih- ,Q- ,u- ,y- fo’ys"k.k vk¡dM+ksa ls fy;k x;k gSA ;g izfr:fir fun’kZ 954 gSDVkikLdy ij izkIr fd, x, leqnz ry ds e/; nkc vkSj 58 feuV izfr lSdaM dh vf/kdre iouksa ds lkFk mM+hlk esa vk, egkpØokr dh fodklkRed fLFkfr;ksa dks izLrqr djrk gSA bl fun’kZ ls vfuok;Z vfHky{k.kksa uker% m".k ØksM] dsanz vkSj dsanz fHkfRr izfr:i.k] gjhdsu ØksM iouksa dks izkIr fd;k x;k gSA ;g fun’kZ pØokr ds LFky Hkkx esa izos’k djus ds mijkar ml LFky ds fudV 40 ls-eh- izfrfnu dh vf/kdre o"kkZ dk iwokZuqeku yxk ldrk gS A ;g fun’kZ 24 ?kaVksa es 120 fd-eh- =qfV;ksa vkSj 120 ?kaVksa esa 0 fd-eh- dh deh ds lkFk egkpØokr ds iFk dk ,dne lgh vkdyu izLrqr djrk gSA In this study NCAR MM5 with the cumulus parameterization scheme of Kain-Fritsch is used to simulate the evaluation of Orissa Super Cyclone for the period 25-30 October 1999. The NCAR MM5 with two-way nested horizontal domains of 90, 30 and 10 km are integrated for five days starting from 0000 UTC of 25 October, 1999. The initial and boundary conditions for this study have been taken from NCEP FNL analysis data available at 1° resolution. The model simulation produces the development of the Orissa Super Cyclone with attained central sea level pressure of 954 hPa and maximum wind of 58 msec-1. The essential characteristics such as warm core, eye and eye-wall simulation, hurricane core winds were obtained by the model. The model could predict a maximum rainfall of 40 cm/day near the landfall point. The model produces a very good estimate of track with errors of 120 km at 24 hours and decreasing to 0 km at 120 hours.

Numerical prediction of the Orissa super cyclone (1999) : Sensitivity to the parameterisation of convection, boundary layer and explicit moisture processes

& ih- ,l- ;w- @ ,u- lh- ,- vkj- ,e- ,e- 5 dk mi;ksx djds mM+hlk esa 1999 esa vk, egkpØokr dh xfrfof/k;ksa vkSj mldh rhozrk ds la[;kRed iwokZuqeku dk bl 'kks/k&i= esa v/;;u fd;k x;k gSA laogu] xzgh; ifjlhek Lrj vkSj fuf’pr ueh Ldheksa dh izkpyhdj.k ;kstukvksa dh Hkwfedk dk v/;;u djus ds fy, laosnu’khyrk iz;ksx fd, x, gSaA caxky dh [kkM+h esa 90] 30 vkSj 10 fd-eh- {kSfrt varjkyksa ds rhu ikjLifjd iz{ks=ksa ¼Mksesu½ dk irk yxkus ds fy, bl ekWMy dh ifjdYiuk dh xbZ gSA ,d va’k ds varjky ij miyC/k gq, ,u- lh- bZ- ih- ,Q- ,u- ,y- vk¡dM+ksa dk mi;ksx djds izkjafHkd {ks=ksa vkSj fHkUu le; ds ifjlhek ifjorhZ rFkk 12 ?kaVs ds varjky ij leqnz lrg rkieku miyC/k djk, x, gSaA laogu] xzgh; ifjlhek Lrj vkSj fuf’pr ueh izfØ;kvksa ds laca/k esa pØokr ds ekxZ dk iwokZuqeku vkSj mldh rhozrk dh laosnu’khyrk dk v/;;u djus ds fy, rhu iz;ksx fd, x, gSaA blls izkIr gq, ifj.kkeksa ls pØokr ds ekxZ ds iwokZuqeku esa laoguh; izfØ;kvksa dh egRoiw.kZ Hkwfedk dk irk pyk gS rFkk dSu&fÝ’k 2 Ldhe ls pØokr ds ekxZ dk lcls lVhd <ax ls irk yxk;k tk ldk gSA blds vykok ;g irk pyrk gS fd xzgh; ifjlhek Lrj izfØ;k,¡ esyj&;eknk Ldhe ds lg;ksx ls lcls izpaMre pØokr dh rhozrk dks Kkr dj ldrh gSaA fuf’pr ueh izfØ;k,¡ pØokr dh xfr dks fu;af=r djrh gSa tks Hkhrjh iz{ks= ¼Mksesu½ ds 10 fd-eh- ds lw{e foHksnu ds QyLo:Ik laHko gks ldrk gSA dSu&fÝz’k 2 vkSj esyj&;eknk dh la;qDr pj.kc) ;kstuk ls pØokr ds ekxZ vkSj mldh rhozrk ds laca/kksa dks csgrj <ax ls izfr:fir fd;k x;k gSA fdlh ,dek= iz;ksx dh rqyuk esa lHkh feystqys iz;ksxksa ls pØokr ds ekxZ vkSj mldh rhozrk dk csgrj vkdyu fd;k tk ldk gSA izfr:fir pØokr esa ,diw.kZ fodflr pØokr ds] m".k ØksM] dsanz vkSj dsanz&fHkfRr tSls lHkh y{k.k ik, x, gSaA ekWMy ls izfr:fir o"kkZ forj.k vkSj rhozrk izs{k.kksa ds vuq:Ik ikbZ xbZ gSA Numerical prediction of the movement and intensification of the Orissa Super Cyclone (1999) is studied using PSU/NCAR MM5. Sensitivity experiments were made to study the role of the parameterisation schemes of convection, planetary boundary layer and explicit moisture schemes. The model is designed to have three interactive domains with 90, 30 and 10 km horizontal resolutions covering the Bay of Bengal region. The initial fields and time varying boundary variables and sea surface temperatures at 12 hour interval are provided from NCEP FNL data available at 1° resolution. Three groups of experiments were performed to study the sensitivity of the cyclone track prediction and intensification to the schemes of convection, planetary boundary layer and explicit moisture processes. The results indicate that convective processes play an important role in the cyclone track prediction and the scheme of Kain-Fritsch 2 produces the best track and the planetary boundary layer processes control the intensification with the scheme of Mellor-Yamada producing the strongest cyclone. The explicit moisture processes modulate the movement of the cyclone, which may be due to the fine resolution of the 10 km for the innermost domain. The mixed-phase scheme in combination with Kain-Fritsch 2 and Mellor-Yamada produce the best simulation in terms of the track as well as intensification. The ensemble mean of all the conducted experiments estimate the track positions and intensification better than any individual experiment. The simulated cyclone shows all the characteristics of a mature cyclone, with warm core, formation of the eye and eye wall. The model simulated rainfall distribution and intensity have good agreement with the observations.

Development of a Monsoon Depression and Its Interaction with the Large-Scale Background: A Case Study

Structure and time evolution of the large-scale background and an embedded synoptic-scale monsoon depression and their interactions are studied. The depression formation is preceded by a cyclonic circulation around 400 hPa. The Fourier-based scale separation technique is used to isolate large (wavenumbers 0–8) and synoptic-scale (wavenumbers 12–60). The wavelength and depression center is determined objectively. The synoptic-scale depression has an average longitudinal wavelength of around 1900 km and a north–south size of 1100 km; it is most intense with a vorticity of 20.5 × 10 −5 s −1 at 900 hPa. The strongest cold core of −3.0°C below 850 hPa and the above warm core of around 2.0°C are evident. The depression is tilted southwestward in the midtroposphere with no significant vertical tilt in the lower troposphere. The mean maximum intensity and upward motion over the life cycle of depression are in close agreement with the composite values. A strong cyclonic shear zone is developed in the midtroposphere preceding the depression. The necessary condition for barotropic (baroclinic) instability is satisfied in the midtroposphere (boundary layer). Strong northward transport of momentum by the depression against the southward shear is found. The strong growth of the MD in the lower troposphere is due to downward transfer of excess energy gained in the midtroposphere from the barotropic energy conversion and east–west direct thermal circulation as the vertical energy flux. The baroclinic interaction contributes to the maintenance of the cold core in the lower troposphere. The diabatic heating rate is computed and its role in the genesis and growth of MD is investigated.

Analysis of the Transition of an Explosive Cyclone to a Mediterranean Tropical-like Cyclone

This study investigates the dynamics of the development phases of a Mediterranean tropical-like cyclone (medicane) in the southern Ionian Sea, on 28 September 2018 that caused high impact phenomena in the central and eastern Mediterranean, focusing on the transition from explosive cyclone to medicane. The symmetry and the warm core structure of the system have been demonstrated via phase space diagrams determining three phases of the system development that are then supported on a dynamical basis. During the first phase of the system, baroclinic instability triggered the formation of the explosive cyclone, when strong upper-level PV anomalies at the dynamic tropopause level moved towards a pre-existed area of enhanced low-level baroclinicity over the coastal areas of Libya along with positive SST anomalies. The surface frontal structure was enhanced under the influence of the upper-level dynamic processes. During the second phase when the medicane formed, low-level diabatic processes determined the evolution of the surface cyclone, without any significant support from baroclinic processes in the upper troposphere. The distortion of the low-level baroclinicity and the frontal structure began after the initial weakening of the upper-level dynamics. During the third phase, the system remained barotropic, being affected by similar mechanisms as in the second phase but with lower intensity. The transition mechanism is not only the result of the seclusion of warm air in the cyclone core but, mainly, the continuation of an explosive cyclone or an intense cyclone when the occlusion began to form.