Crop yield in India in relation to EI-Nino

ABSTRACT. Association between the EI- Nino events in the Pacific Ocean and the crop yields in India has been examined. Five districts,viz. Churu, Gwalior, Rewa, Palamau and Bankura located on the normal monsoon trough zone and cultivating altogether different, mostly rainfed crops, were selected for the study. Crop and seasonal rainfall data from 1951-88 were utilised in the analysis. The results indicate that the EI-Nino phenomenon does not exert much influence on the kharif. In wave models with cons crops in India.

PLANETARY BOUNDARY LAYER STRUCTURE IN THE MONSOON TROUGH REGION

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.

SODAR STUDIES OF THE MONSOON TROUGH BOUNDARY LAYER AT JODHPUR (INDIA)

A monostatic sodar was set up at Jodhpur, the extreme end of the monsoon trot*, to study the thermal boundary layer up to a height of 700 m. This effort was a part of the co-ordinated multi institutional project to study the monsoon dynamics. The usual structures of thermal plumes, ground based stable layers, elevated/multi- layers with or without undulations and dot echoes were seen. However, erosion of the inversion layer normally observed in the morning in the form of a rising layer over land areas was absent all through the period of observation from June to August 1990. In the paper, a study of the observed data in relation to the rainfall activity has been made. A preliminary examination shows that sodar structures may provide addi• tional information, not available normally through the conventional meteorological tools.

An insight into the severe floods in India during 2005, 2006 & 2007

In this paper severe flood during South West monsoon seasons of 2005, 2006 & 2007 have been identified with the related synoptic features. A total of 22 states reeled under severe floods during 2005, 2006 & 2007. In the south peninsula only Karnataka and Kerala were affected by severe floods. During 2006 & 2007 severe floods continued for a longer period and affected many states where as during 2005 severe floods affected most of the states except peninsular India but they continued for short periods comparatively.Formation of excess No’s of low pressure areas and depressions in the Bay of Bengal during July, Aug and Sept 2006, in succession , and their WNW movements upto M.P. and east Rajasthan caused severe floods in Gujarat, Maharashtra, Rajasthan, Madhya Pradesh, Chattisgarh, Orissa and Andhra Pradesh for a longer period i.e. from 28 July to 12 September 2006. During 2007, Shifting of monsoon trough, presence of secondary monsoon trough and trough in westerly, caused severe floods in most of the North eastern states from 12 July to 10 October 2007.

Variation of boundary layer heights and eddy diffusivities over dry and moist convective regions of monsoon trough during different phases of monsoon

Temperature, wind, and humidity data at 6 levels over meteorological towers at Kharagpur and Jodhpur and fast data at Jodhpur (Sonic anemometer at 4m and Gill anemometer 15 m) and Kharagpur (Sonic anemometer at 8m and Gill anemometer at 15m) were analysed. Diurnal variation of boundary layer heights and eddy diffusivity coefficient of moment, heat and moisture at dry convective region Jodhpur (26° N, 73°E) and moist convective region Kharagpur (22.3°N, 87.2°E) of monsoon trough during onset of monsoon, mid-monsoon and end-monsoon phases of the Indian southwest monsoon are studied using micro meteorological tower data. Boundary layer height is computed by eddy correlation (direct method) and profile method {indirect method). Indirect method underestimates the boundary layer height.

Monsoon variability in recent years from synoptic scale disturbances and semi-permanent systems

In the recent decade from 1987 to 1996, the Indian summer monsoon rainfall has shown less interannual variability in comparison with its earlier decade. Except 1987 and 1988, the area weighted average monsoon rainfall of all other years are within 10% (normal) of its long period average value over India. The paper discusses monsoon rainfall and several other associated circulations features with their variability in interannual scale during 1987-96. The results show that though the variability of monsoon rainfall is less during the decade, there is a significant interannual variation in the number of synoptic systems, their days, intensities and number of days of presence of monsoon trough and Tibetan anticyclone. The years with positive side (negative side) of normal seasonal rainfall are characterised by more (less) number of days of synoptic disturbances and more (less) number of days of presence of monsoon trough and Tibetan anticyclone in their favourable positions. However, overall activity of heat low, tropical easterly jet and sub-tropical westerly jet in the season have no direct relation with seasonal monsoon rainfall. In addition, the dates of onset and withdrawal of monsoon over India and the number of days monsoon took to over all India also have no relation with the monsoon rainfall.

Daily summer monsoon rainfall over northeast India due to synoptic scale systems

The summer monsoon rainfall over northeast India mostly depends on the synoptic systems over the region and neighbourhood and the convection due to the interaction of orography with the synoptic and sub-synoptic scale systems. Hence, an attempt is made to analyse the mean daily rainfall distribution over northeast India due to different synoptic systems like Low Pressure Systems (LPS) and cyclonic circulations (cycir) extending upto lower/middle tropospheric levels over different regions. The mean daily rainfall due to monsoon trough over various locations in northeast India is also analysed. For the above purpose, the rainfall data over 50 uniformly distributed stations in northeast India during summer monsoon season (June-September) for a period of 10 years (1991-2000) are considered. The principal objective of the study is to find out the contribution of the different synoptic systems to the spatial variability of monsoon rainfall over northeast India. The developed synoptic analog maps may be useful to the forecasters for 24 hours rainfall forecast with the knowledge of location, intensity and movement of the synoptic systems. Based on larger data set, the results confirm the earlier findings (Srinivasan et al., 1972) with respect to rainfall due to monsoon trough and LPS. The Low Level Cycir (LLC) also plays significant role on the rainfall variability over northeast India, as the number of LLC days is significantly higher over the region, contrary to the days of occurrence of LPS. The study finds out the regions of excess/deficient rainfall and active/weak monsoon conditions due to different synoptic systems.

Relative contribution of synoptic systems to monsoon rainfall over Orissa

ABSTRACT. The low/depression over northwest (NW) Bay of Bengal is the largest contributor to seasonal monsoon rainfall over all stations in Orissa and Orissa as a whole. The Low Pressure Systems (LPS) and cyclonic circulation (cycir) extending upto 500 hPa level over NW Bay of Bengal alone contribute about 22% to the seasonal monsoon rainfall through about 12 days. The monsoon trough without any significant embedded systems over Orissa and adjoining regions contributes about 28% to seasonal rainfall through about 55 days. All types of LPS including low, depression and cyclonic storm yield maximum rainfall in their left forward (southwest) sectors. The maximum rainfall belt lies more southward due to a depression compared to that due to a low. The spatial distribution of rainfall due to cycir is less systematic. The interaction due to Eastern Ghat plays a significant role in spatial distribution of rainfall over western and eastern sides of the Eastern Ghat due to monsoon lows and depressions over Orissa and adjoining Bay and land regions. The orographic interaction due to Eastern Ghat with the cycirs over Orissa and adjoining Bay and land regions is significantly less leading to no significant difference in spatial distribution of rainfall over eastern and western sides of the Eastern Ghat.