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Understanding Rapid Intensification (RI) is crucial for improving the Tropical Cyclone (TC) intensity forecast skill and TC induced disaster preparedness. The physical processes that lead to RI are not well studied over the North Indian Ocean (NIO) region. Two TC cases, i.e., Titli (exhibited RI) and Phethai (not exhibited RI) from the 2018 post-monsoon season are considered to understand the environmental conditions responsible for making RI happen. The Hurricane Weather Research and Forecasting (HWRF) model produced simulations for Titli and Phethai are analyzed to understand the intensification changes. The purpose of this study is to investigate the environmental and storm structure characteristics that led to the RI of TC Titli when compared to TC Phethai. The Phethai and Titli simulations are initially validated against the best estimations by India Meteorological Department (IMD) and compared in terms of the environmental vertical wind shear as this parameter is often negatively correlated with TC intensification. Area averages of the deep-layer and mid-layer vertical wind shear over the TC environment suggest that shear did not affect the intensification of the Titli simulation. Initially, Titli contained higher magnitudes of relative humidity throughout the troposphere within the storm’s circulation. This steered to a higher upward mass flux in the troposphere and rapid intensification of relative vorticity (circulation) in the middle troposphere prior to any significant change ensued at the surface. After a deep vortex was established, the mass flux (and lower-tropospheric convergence) continued to rise, leading to RI. These results offer a basis for future research to understand better and forecast the development of RI.

A study has been undertaken to find out different characteristics like frequency, intensity, movement, region of occurrence etc. of low pressure systems (LPS) including low, depression and cyclonic storm etc. developing over Orissa and neighbouring sea and land regions during excess and deficient monsoon rainfall months (June – September) over Orissa. The study is based on data of 20 years (1980-1999). The principal objective of this study is to find out the contribution of LPS to extreme monsoon rainfall activity over Orissa. The number of LPS days rather than frequency of formation of LPS over different regions better explain the excess and deficient rainfall over Orissa. The excess rainfall over Orissa during June is not significantly related with the number of LPS days. Significantly less than normal number of LPS days over northwest (NW) Bay of Bengal and Gangetic West Bengal (GWB) and higher number of LPS days over west central (WC) Bay off north coastal Andhra Pradesh (NCAP) cause deficient rainfall over Orissa during June. While significantly higher than normal number of LPS days over NW Bay and Orissa leads to excess rainfall during July, less than normal number of LPS days over WC Bay off NCAP is associated with excess rainfall during August. The less number of LPS days over Orissa due to less frequent movement of LPS across Orissa from the Bay of Bengal leads to deficient rainfall over Orissa during both July and August. Significantly higher/less than normal number of LPS days over NW Bay leads to excess/deficient rainfall over Orissa during September.

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.

& 29 vDrwcj] 1999 dks mM+hlk ds rV ij vk;k egkpØokr mM+hlk ds vc rd ds bfrgkl dk lcls izpaM rwQku Fkk ftldh 250 fd-eh- izfr ?kaVk dh rhoz xfr okyh iouksa us jkT; ds 12 rVh; ftyksa dks rgl&ugl dj MkykA rwQku ds LFky ls Vdjkus ds i'pkr~ 36 ?kaVs ls Hkh vf/kd le; rd iouksa dh izpaMrk cuh jghA bl rwQku ls tku eky dk dkQh uqdlku gqvkA yxHkx 10]000 yksxksa dh tkusa xbZA bl v/;;u esa rwQku ds eslksLdsy izfr:Ik dks csgrj cukus ds fy, dqN egRoiw.kZ igyqvksa dh tk¡p gsrq O;kid la[;kRed iz;ksx fd, x, gSaA bu igyqvksa esa xSj nzoLFkSfrd xfrd] fun’kZ {kSfrt foHksnu vkSj egRoiw.kZ izR;{k izfØ;kvksa ds izkpyhdj.k 'kkfey gSaA rwQku dk 5 fnolh; izfr:Ik ¼123 ?kaVksa ds yxkrkj lekdyu½ rS;kj djus ds fy, eslksLdsy fun’kZ ,e- ,e- 5 dk mi;ksx fd;k x;k gSA blesa le:ih foHksnu ¼30 fd-eh-½ vkSj le:ih le; J`a[kyk ds lkFk nzoLFkSfrd ¼,p-,l-½ rFkk xSj nzoLFkSfrd ¼,u- ,l-½ xfrdksa ds lg;ksx ls rwQku ds izfr:i esa xSj nzoLFkSfrdrk ds izHkko dh tk¡p dh xbZ gSA bl fof/k ls rwQku vkSj fo’ks"k :Ik ls bldh rhozrk dk xSj nzoLFkSfrd xfrdksa ds lkFk lgh izfr:i.k gksrk gSA xSj nzoLFkSfrd xfrdksa ds lkFk 90 fd-eh-] 60 fd-eh- vkSj 30 fd-eh- ds foHksnuksa ij rwQku dk izfr:i.k djrs gq, fun’kZ dh laof/kZr {kSfrt foHksnu dh egRrk dh tk¡p dh xbZ gS vkSj rwQku ds izfr:i.k esa bldk izR;{k izHkko ns[kk x;k gSA egRoiw.kZ izR;{k izfØ;k okys diklh laogu xzgh; ifjlhek Lrj ¼ih- ch- ,y-½ vkSj fofdj.k gsrq fun’kZ esa miyC/k izkpyhÑr ;kstukvksa ds csgrj lEHkkO; leUo; dk irk yxkus ds fy, la[;kRed iz;ksx Hkh fd, x,A lh- lh- ,e- 2 fofdj.k izkpyhÑr ;kstuk lesr xzsy diklh laogu vkSj gk¡x&isu ih- ch- ,y- ;kstuk ds lkFk leUo;u okyh ;kstuk ds vU; ijhf{kr ;kstukvksa dh rqyuk esa lcls csgrj ifj.kkeksa dk irk pyk gSA The super cyclone that crossed Orissa coast on 29 October 1999 was the most intense storm in the history of Orissa with 12 coastal districts of the state were battered by winds reaching 250 kmph. The fury of winds continued for more than 36 hours after landfall of the storm. The storm caused huge damage to properties and nearly 10,000 people lost their lives. In the present study, extensive numerical experiments are conducted to investigate some important aspects that may lead to the improvement in mesoscale simulation of the storm. The aspects that are addressed here include non-hydrostatic dynamics, model horizontal resolution and parameterization of important physical processes. The mesoscale model MM5 is used to produce 5-day simulation of the storm. The influence of non-hydrostaticity is investigated by simulating the storm with hydrostatic (HS) and non-hydrostatic (NS) dynamics at same resolution (30 km) and with same time step. The storm, in particular its intensity is better simulated with non-hydrostatic dynamics. The importance of increasing model horizontal resolution is investigated by simulating the storm at 90 km, 60 km and 30 km resolutions with non-hydrostatic dynamics and found to have perceptible impact in simulation of the storm. Numerical experiments also are conducted to find the best possible combination of the parameterization schemes available in the model for the important physical processes cumulus convection, planetary boundary layer (PBL) and radiation. The combination of Grell cumulus convection and Hong-Pan PBL scheme along with CCM2 radiation parameterization scheme is found to provide the best result compared to the other schemes tested.

Northwest India is comprised of various Himalayan mountain ranges. These ranges are having different altitude and orientations all along this region. During winter season enormous amount of precipitation is received in this region due to westward moving low pressure synoptic weather systems called Western Disturbances (WD). Variable terrain gives rise to low level circulation during the passage of these systems. Surface weather elements like temperature, pressure and relative humidity are highly dependent on local topography. To draw projected weather, uncertainties involved in the relationship between upper level circulation and surface weather is tried to be formally expressed in statistical terms. Perfect Prognostic Method (PPM) is used to forecast Probability of Precipitation (PoP) occurrence, followed by Quantitative Precipitation Forecast (QPF) model. The objective is to give projected weather in lead time of 24 hour at one of the specific sites, Sonamarg, situated in Great Himalayan range. Analysis data from the National Center for Environmental Prediction (NCEP), US and station data of three stations from India Meteorological Department (IMD), India is used for development of model. Data of December, January, February and March (DJFM) months for 12 year (1984-96) is taken for developmental mode. Whereas IMD data with (i) NCEP analysis, (ii) NCMRWF analysis and (iii) NCMRWF’s T80 day 1 forecast for DJFM months for 1996-97 is considered for the verification purpose. Result shows that PoP model could predict with 90.4% accuracy for developmental set, whereas in verification cases best prediction is made with accuracy of 86.8%. In case of QPF model percentage correct forecast is made with 45.0% in developmental set, whereas maximum 54.2% accuracy is achieved in verification sample.

Onset of south west monsoon (SWM) over Kerala is associated with intense convection followed by heavy rainfall over the west-coast of India. The intense rainfall events are usually associated with meso-scale convective systems embedded in large scale synoptic system over the Arabian Sea. Such deep and intense cumulus convection can have an important effect on the dynamics and energetics of large-scale atmospheric systems, because of the large magnitudes of the energy transformations associated with changes of phase of water in precipitating cumulus clouds as well as the strong updrafts and downdrafts in the troposphere. The prime objective of this study is to understand the convective structure (active/suppressed) of the atmosphere over the west-coast of India during ARMEX-I (Arabian Sea Monsoon Experiment). This study uses an approach to obtain the average structure of a cloud cluster and its interaction with the environment that enables in distinguishing the variation of kinematic and convective parameters from suppressed to convectively active process. Upper air observations obtained from four coastal land stations viz., Bombay, Goa, Mangalore and Trivandrum, alongwith that obtained over ORV Sagar Kanya are used to calculate both the convective and the kinematic parameters at the centre of the polygon formed by these observation locations. Time averaged circulation kinematic parameters and vertical velocity during active and suppressed convective phases off the west coast of India were discussed. The apparent heating and the apparent moisture sink are also estimated through residuals of the thermodynamic equations during intense and weak phases of SWM.

Arabian Sea Monsoon Experiment (ARMEX) 2O02 was carried out from mid June to mid August to study the presence of off-shore trough (OST) and embedded vortices. Four cases of heavy rainfall along the west coast (rainfall exceeding 12 cm in 24 hour) of India were recorded on 14-16 June, 20-22 June, 26-28 June and 7-10 August 2002. The heavy rainfal1 event of 26-28 June was due to a low pressure system that moved from Bay of Bengal across Madhya Pradesh to Gujarat and adjoining Rajasthan. The other three heavy rainfall events were associated with the off shore trough and /or off shore vortices. Of the various sea buoys deployed in the Arabian Sea, only one buoy located off Goa, did give hint of an OST both in strong and weak wind conditions. However, surface wind data from other buoys and QSCAT surface wind did not always support the presence of OST. The indications were very subtle and it was found difficult to observe them on the NCMRWF (National Centre for Medium Range Weather Forecasting) analysis or forecast charts. In the present study it has been observed that off shore trough may be observed in weak as well as strong monsoon conditions. However, heavy rainfall events were noticed only when the monsoon current is strong both in the Arabian Sea as well as Bay of Bengal in association with some synoptic systems. In addition, an east-west shear line in wind flow pattern extending from lower to middle or upper tropospheric levels and joining the circulation features in the Arabian Sea and Bay of Bengal has been noticed in all cases of heavy rainfall events. Meso-scale vortices/organized convection systems were also identified during heavy rainfall events on the basis of cloud features noticed in the satellite pictures and TRMM rain rate patterns.

An attempt is made to numerically simulate one heavy rainfall event observed during 7-9 August 2002 along the west coast of India using mesoscale modeling system (MM5). The prime objective of the present study is to investigate the impact of analysis nudging using conventional and non-conventional observations at high-resolution in the mesoscale model. Two numerical experiments are carried out with MM5 having a double nested domain viz. 60 km (coarse) and 20 km (inner) to study this heavy rainfall event. The first experiment, namely the control simulation (CNTL), global analyses is used as initial and boundary conditions. It is noticed that the model is not able to comprehensively capture the prominent features associated with organized convective processes. A second experiment, called the nudging simulation (NUDG), is carried out where the model initial and boundary conditions are improved after the insertion of observational data. Thereafter, 12 hrs analysis nudging is also applied to further improve the initial condition, before the model is allowed for free integration. Results indicate that the simulations are improved when four dimensional data assimilation using analysis nudging is performed.

During ARMEX-I several special observations were taken over Arabian Sea region and adjoining west coast of India, which gave an opportunity to study this region more thoroughly. To handle such voluminous data, ARMEX data center has been established at National Centre for Medium Range Weather Forecasting (NCMRWF), in collaboration with India Meteorological Department (IMD) and Indian Institute Technology (IIT), Delhi. One of the tasks of this center is to produce reanalysis for ARMEX period, utilizing these observations. It is essential to assimilate every observation from all available sources, especially over the data sparse oceanic regions for accurate determination of the three-dimensional structure of the atmospheric circulation. Before assimilating these data in global data assimilation system of NCMRWF, an attempt has been made to validate some of these data against observational facts from other sources. Upper-air observations (Digicora) from Dabolim, Goa have been compared with RS/RW observation of IMD, at Panjim, Goa. Though the trend in variations of all the meteorological parameters of these two stations is similar but there is a large difference in their absolute values. Reanalysis generated using the specially collected upper-air observations have been compared with the operational analysis of NCMRWF. The impact of these special observations on analysis and forecast system is found to be confined over the Arabian Sea region only in the lower troposphere. However, in the upper troposphere and stratosphere the impact is seen also over the equatorial Indian Ocean region.

The Arabian Sea Monsoon Experiment (ARMEX) addresses monsoon and associated convective activity, laying emphasis on the monsoon onset processes and intense rainfall events over the west coast of India. The prime objective of this paper is to study the variation observed in the surface and upper air parameters obtained over the west-coast of India during ARMEX. Conserved Variable Analyses (CVA) of viz., potential temperature, virtual potential temperature, saturation equivalent potential temperature and specific humidity etc. were also carried out at every point up to 3 km from the surface to cover the boundary layer over convectively active and suppressed regimes along the west-coast of India during this period. Analyses of the surface parameters such as sea-surface temperature (SST), air temperature, wind speed and moisture along the ORV Sagar Kanya (ORVSK) cruise track were carried out. Similar analysis was also carried along a few of the west-coast land stations viz. Vijaydurg, Karvar, Honavar and Goa. The structure of the boundary layer was found to be varying depending on the various factors that influence lower atmosphere and the general trend being a pronounced increase in the boundary layer height during an active convection process just before the heavy rainfall event.

In this study, an attempt is made to develop an objective method for forecasting the direction and speed of the gusty winds associated with thunderstorms at Delhi. For this purpose, surface and upper-air data for April, May and June (AMJ) for the years 1985-90 are utilized. Multiple regression equations are developed for forecasting the direction and speed of the gusty winds, using stepwise screening method, for which a total of 181 potential predictors are utilized. The developed dynamical-statistical models are tested with independent data sets of 1994 and 1995 for April, May and June. The dynamical-statistical models give satisfactory results with the developmental as well as the independent data sets. The root mean square error of the direction vary between 58° and 77° and the speed forecast vary between 9 and 12 knots. Possible reasons for large deviations of the forecast, noticed on a very few occasions, have also been examined.

At present the approach to forecasting visibility is synoptic and personal experience of the weather forecaster. The month of December typically a winter month, is associated with poor visibility. Aviators require visibility forecast in terms of a definite quantitative value at a specific place in specific time frame. Therefore, in this study an attempt is made to develop a suitable model for forecasting visibility in December at a place Hindon near Delhi in a quantitative manner. In the development process of forecasting visibility, different approaches such as auto-regression, multiple regression, climatology and persistence have been attempted. The models are developed using seven years (1984-90) data of December. The model is evaluated with the independent data sets from the recent years 1994-95. It is found that climatology-persistence method provides better results as compared to the multiple regression and auto-regression methods. The developed model provided positive skill scores as high as 70% on development as well as independent data sets.

The performance of a Global Spectral Model (T-80) operational at the National Centre for Medium Range Weather Forecasting (NCMRWF), New Delhi in predicting the cyclogenesis of six tropical cyclones over Indian Seas formed during 1995-96 has been evaluated. It has been found that the model has the capability to predict cyclogenesis in wind field at least 72 hours in advance although the positions of predicted vortices are seen to be displaced from those of analysed ones in some cases. The quantitative estimates of the atmospheric conditions favourable for cyclogenesis also confirm the conclusions drawn from the qualitative analysis of cyclogenesis predictions of the model in terms of appearance of cyclonic circulation. It also follows from this analysis that the predicted circulations at the cyclogenesis stage are in general more intense and stronger as compared to the corresponding analysis in terms of wind and mass fields. On examining the model systematic errors of prediction it is found that the model has a clear bias for predicting more intense vortex during genesis and weakening stages. On the order hand it predicts relatively less intense vortex during intensification process.

The severe cyclonic storm with a core of hurricane winds of 4-11 May 1990, which crossed the Indian east coast near Machilipatnarn (Andhra Pradesh), was one of the most intense cyclones in recent years over the Bay of Bengal region of the north Indian Ocean. The storm reported the minimum sea level pressure of 912 hPa, the lowest observed value for any cyclone in the region. The storm exhibited certain interesting structural characteristics. The most striking feature observed was the formation of secondary convective rings wrapped around the primary eyewall. These features were observed for nearly two days by four cyclone detection radars (CDR) located on the east coast of India. The paper presents an analysis of these features. We find that the double eye-wall structure of the storm has undergone a repetitive cycle characterized by the contraction of the outer eyewall and the weakening of the inner eyewall during the life of the cyclone. These interesting characteristics are observed for the first time in the north Indian Ocean for any cyclone. Some of the related aspects of double eyewall features, such as, the possible role of double eyewall structure on the recurvature or turning of the storm and the effect of land obstacle in the development of a secondary eyewall are discussed.

A ~IUt ly of PbllWIHI") lt cundury l.nycr (PUll in the lIIunsllun llflllgh !"l'l:illll ha:oo h! 't'11 Carrl,'t11l1l1based on MONTDl EX 1989 pilot experiment d ata PilI. structure over land !>hllw'IO lAid l' , pati,11 lIn,1 tem poralvariatums. TIlrCCtypes of PRL- .'IOha llu\oli convective . monsoon ~11111 111) convective boundaryl a yers haw been obv-rved. Ch ar act eri st ic features :I!I:"Ul"i:JI~lt wilh Jill"t'relll types of POL have been iJe- l\lilit... 1and p rcscnr c..t in th e p:Jlll'r.With the help of observe...1rill ,structure over-eastern. ceutral and wcsrcm M'11m suf llu' ll1tlll~ IHn tmullii. ;1111"'1111'1hash«'11 made to develop "PlIl '(" e ro s e-sec tio ns of PUL UH'r Ind o -G a ngetic plains llu rilli' act ive. wcuk ,lilt' bren kmonsoon co nd itio n s.

The thermodynamic structure of boundary la)l:r over Calcutta on the eastern secto r of the monsoontrough has been exam ined byint~ratina I one-dimensional TKE closure planetary bound ary laye r model fortropics which inJcudes interaction oCclo udiness and radiation with turbulence and counter , radient transports ofheal moistu re and momentum. Data sets cf pilct-esperiment phase ofMONTBLEX in 1988 have been used formispurpo se. two specific situations, o ne 'When liquid water is present and the other ~tlcn very strona: winds are prevailinain the boundary layer 8~ considered. Diurn al varialion oCturbulent kinetic ener'ly.lhe TKE budget and the veelicalprofiles otTKE and eddy exchange coefficient ha ve revealed the importance DC counter gradient transports notonly aCheat and moisture but also oC momentum. Combined role DC presence of liquid water and counter gradientsin buoyant production and role of counter a:radienu of momentum in shear production have beenestablished.

A coastal zone numerical model has been used to estimate the surge generated by the 67 June 1982 Orissa cyclone. In this model the analysis area extends from 6 N to about 22 N along the east coast of India and there is an open-sea boundary situated, on average, about 300 km from the coast The model utilises a curvilinear boundary treatment to represent the coastlines and uses a non-uniform off-shore grid-spacing adjacent to the coastal boundaries. This allows an increased resolution near the Orissa coast. Using a forcing wind-stress distribution representative of the Orissa cyclone, we compare the model predicted surges with the observed sea-surface elevations along part of the Orissa coast north of Paradip. The predicted peak surge elevation above mean sea level compares well with the observed values at the Paradip port and Dhamra harbour.

A number of numerical experiments are carried out to find a suitable dynamic initialization scheme for tropics. The experiments are carried out with a multi-level primitive equations model with sigma as the vertical coordinate. The performance of different initialization schemes are evaluated from the initialized 12 and 24 hours forecast fields. It is found that all the different types of dynamic initialization yield almost, similar results. However, on the basis of the overall performance and computational economy considerations, the Okamura scheme is preferred.

Using the data on air and sea surface temperature and total cloud cover recorded of the country, by a fixed polygon of ships over the Bay of Bengal during MONEX-79 from 11 to 23 July 1919, the effective long-wave radiation from the sea surface was calculated by a semi-empirical relation. This relation was found to agree satisfactorily with observed values of outgoing radiation during Monsoon- 77. A statistical analysis revealed very good negative correlation between the effective outgoing radiation and the total cloud cover (N). In view of this correlation, we performed a spectral analysis of the effective outgoing radiation and the total cloud cover. The paper presents the results of the spectral analysis, including the square of the coherency and the phase difference between these two variates.

A number of empirical expressions have been used to estimate the effective outgoing long wave radiation from a sea surface. We have used the observations recorded during the Indo-USSR Monsoon Experiment of 1977 to test the efficiency of these expressions, We find that an expression derived by Girduk et at. ( 1973) tends to provide a better fit with the actinometric observations than the other empirical expressions currently in use.

The effect of large scale moisture and moist static energy (MSE) budget on the onset and activities of summer monsoon is investigated. The data base for this study consists of twice daily First GARP Global Experiment (FGGE) level IIIb analysis of temperature, relative humidity, geopotential and wind fields for a tropical belt from 20 deg. S to 40 deg. Nand 0 deg. E to 150 deg. E, during May-July 1979. The daily variation, vertical distribution and period averages of the various terms in latent heat energy (LHE) and MSE budget equation are closely examined to find out their influence on the activities of monsoon. The study indicates significant increase in the net LHE, horizontal. Convergence of moisture and diabatic moisture sink (indicator of excess condensation than evaporation) about two week before the onset pf monsoon over Kerala coast. Further, a decreasing trend is observed in horizontal convergence of moisture and moisture sink about one week before the break monsoon condition, which started over India on 16 July 1979. However, the various terms of the MSE budget equation do not depict my significant trend with the advance of the monsoon. The vertical distribution, period averages and the boundary fluxes also confirm the above findings.

An algorithm for computation of the parameters of a quasi-stationary barotropic planetary boundary layer (PBL) IS discussed. On the basis ~f the results of a number of numerical experiments, relations between the observed meteorological fields and the Internal parameters of the PBL have been established. A method is proposed to parameterize eddy momentum flux and frictional vertical velocity for their use in multi-level primitive equations (PE) models.

A numerical procedure is illustrated for computing stream function and velocity potential fields from the vorticity and divergence of the horizontal wind field. A mixed type of boundary condition is suggested in the present work. The computations are performed with a number of existing methods and the method proposed in this study, on a spherical grid over the tropical belt (3.7SN-30N and 45E-105E) with observed wind field as basic input. Horizontal wind fields are reconstructed from the computed fields of stream function and velocity potential and compared with the observed wind field. The results of both qualitative and quantitative intercomparison among the various methods show that the reconstructed total wind obtained by the method suggested in the present study is the best representation of the original observed wind.

During Monsoon- 77 experiment four USSR research vessels collected six hourly RS and RW data, over the Bay of Bengal in August 1977 in a stationary polygon position. This study presents certain statistical characteristics of the meteorological parameters observed during the period.

A number of numerical experiments on dynamical initialization of geopotential and wind fields in the lower latitudes are carried out within the framework of a regional barotropic primitive equation (P .E.) model. In the earlier works of Kivganov and Mohanty 0979) an optimal procedure of dynamical initialization with consideration of an initial-value and boundary-value problem of a P .E. model in the lower latitudes is stated. In this paper with use of this initialization procedure and velocity field as input data some of the important properties of the dynamical initialization in the lower latitudes and the effectiveness of the integration of a P.E. model with the use of balanced data are demonstrated.

The effect of large scale moisture and moist static energy (MSE) budget on the onset and activities of summer monsoon is investigated. The data base for this study consists of twice daily First GARP Global Experiment (FGGE) level IIIb analysis of temperature, relative humidity, geopotential and wind fields for a tropical belt from 20 deg. S to 40 deg. Nand 0 deg. E to 150 deg. E, during May-July 1979. The daily variation, vertical distribution and period averages of the various terms in latent heat energy (LHE) and MSE budget equation are closely examined to find out their influence on the activities of monsoon. The study indicates significant increase in the net LHE, horizontal. Convergence of moisture and diabatic moisture sink (indicator of excess condensation than evaporation) about two week before the onset pf monsoon over Kerala coast. Further, a decreasing trend is observed in horizontal convergence of moisture and moisture sink about one week before the break monsoon condition, which started over India on 16 July 1979. However, the various terms of the MSE budget equation do not depict my significant trend with the advance of the monsoon. The vertical distribution, period averages and the boundary fluxes also confirm the above findings.