Summertime turbulent heat fluxes at East Antarctica over neighbouring rocky and ice shelf sites

During the ninth Indian Scientific Expedition to Antarctica, in the year 1990, a micro-meteorological tower was installed at Maitri (70° S, 12° E) on the rocky terrain and on an experimental basis, on the nearby ice-shelf at the location of Dakshin Gangotri (70° 7¢ S, 11° 7¢ E). The synoptic features strongly influencing over the sites are the southeasterly katabatic winds from the polar cap and/or northerly low level warm and humid winds from the sea. These flows are responsible for the formation of strong surface based inversion and strong convective conditions at the ice shelf and rocky terrain during the minimum and maximum insolation periods, respectively. This paper presents a study of surface layer structure over two contrasting surfaces on near-coastal Antarctica and deals with the significance of the energy exchange processes over the rocky Antarctic region and the parameterization of turbulent fluxes over surfaces having strong inversion/convection conditions. The paper makes use of turbulence structure functions which are different from the conventional one given by Panofsky and Dutton (1984).

Exceptional heavy rainfall over Ajoy, Mayurakshi and Kansabati catchments and QPF verification during flood season of September 2009

Ajoy, Mayurakshi, Kansabati are three important river catchments of West Bengal and Jharkhand state, received very heavy rainfall during two consecutive days of flood season in the month of September 2009. The contribution of heavy rainfall & combined discharges from Damodar Valley Corporation (DVC) reservoirs during the period of heavy rainspells over these catchments enhanced flood situation in some districts of West Bengal. The synoptic features based on weather charts, cloud imageries of satellite and radar pictures have been taken to analyse. The realized areal average precipitation (AAP) as per rainfall recorded at 0300 UTC of next day have also been taken to verify the quantitative precipitation forecast (QPF) of 6&7 September 2009.

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.

Progression of mid-tropospheric stable layer over Delhi region during May 1989 –A case study

The paper presents details of the formation and di~sipa1ion of upper air inversions between 500 and 300 hPa from 20 to 28 May 1989 over Delhi and adjoining areas and discusses the associated synoptic features.

A diagnostic study of contrasting rainfall epochs over Mumbai

An attempt has made to diagnose the synoptic features and some dynamic and thermodynamic parameters associated with contrasting rainfall situations (on consecutive days) during the monsoon season, over Mumbai. Study has been made for two contrasting monsoon years, viz. 1987 (Bad monsoon year) and 1988 (Good monsoon year). For this study RS data of Mumbai have been used. In many cases heavy rainfall on an isolated day over Mumbai is associated with the following synoptic systems (a) a trough on sea level chart running along west coast through Maharashtra Coast and (b) a cyclonic circulation (CYCIR) over Gujarat in the lower/middle tropospheric level. At least one of the above two systems ceased to exist on the days of light rainfall. Weighted average value of moist static energy is more on the day of heavy rainfall. In most of the cases convective available potential energy (CAPE) is also more on the day of heavy rainfall. LFC, on most of the cases, is seen to have lowered down on the days of heavy rainfall. Variation in upper air flow pattern and scorer parameter also gave very interesting clues to variation of rainfall on contrasting days.

Some characteristics of recurving cyclones of the Indian seas

The present study deals with some of the characteristics of recurving cyclones of the Indian seas like speed, intensity and latitude of recurvature etc. The synoptic features, which are responsible for recurvature, are also studied. Analysis of 200 hPa wind composites indicates some predictive signature atleast 24 hours (IST) prior to recurvature.

Southwest monsoon rainfall in India : Part II - Principal components in temporal domain

An attempt has been made towards objective identification of phases of the southwest monsoon by principal component analysis (PCA) in temporal domain (T-mode). The method utilizes the relationship of weekly rainfall activities with principal components (PCs) of southwest monsoon. Based on the relationships, subgroup of weeks with similar spatial patterns have been identified. Synoptic features of these subgroups have been brought out with the help of synoptic charts. The first four significant PCs are associated with four kinds of active phases of the southwest monsoon when the low pressure systems have typical characteristics corresponding to each PC. Thus, the study suggests a method of interpretation of PCs with the help of synoptic charts by objective identification of phases of southwest monsoon.

Floods in Karnataka during 2009 : A synoptic study

Karnataka a State in south peninsular India receives 73% of its annual rainfall during southwestmonsoon season. Because of the complex physiographical features, the rainfall pattern over the State shows large spatialvariation from 50 to 350 cms. The coefficient of interannual variation of the monsoon rainfall is about 15% over coastalKarnataka (CK) and between 20-30% over interior Karnataka. The precipitation over this State is mainly dominated bysemi permanent systems like off shore trough running along the west coast, low pressure systems forming over the Bay ofBengal during the monsoon season. A well marked low pressure area during 28 September - 3 October 2009 over the Bayof Bengal caused widespread damage to life and property in north Karnataka. In this study, an attempt has been made toexamine the synoptic features of this system that caused heavy rainfall over many districts of the State leading towidespread destruction.

Precipitation regionalization of southwest monsoon by hierarchical cluster analysis

An attempt has been made to identify coherent zones of southwest monsoon rainfall over the Indian region by employing hierarchical cluster analysis. Examination of dendrograms produced by different fusion strategies revealed the presence of 13 nuclei clusters of meteorological subdivisions. Formation of these nuclei clusters could be interpreted by their average principal component (PC) scores and associated synoptic features of PCs. Higher level inter-nuclei joinings have occurred in various fusion strategies to produce different types of clusters of subdivisions. A flexible strategy providing well separated groups of meteorological sub-divisions has been found to be suitable. The method has identified six homogeneous regions of rainfall over India. The meteorological subdivisions have been found to be evenly distributed in these coherent zones. The clustering obtained by this method has been reasonable and largely interpretable.

A Synoptic analogue model to issue QPF over Gangetic West Bengal and adjoining Jharkhand

In this study the Areal Average Precipitation (AAP) data for each day over each of the six catchments of Gangetic West Bengal (GWB) and adjoining Jharkhand namely river catchments of Mayurakhshi, Ajoy, Kansabati, Damodar, Barakar and Lower Valley of Damodar Valley Corporation during monsoon season for 25 years from 1990 to 2014 have been analyzed by grouping the AAP in three different ranges (11-25 mm, 26-50 mm, 51-100 mm and more), excluding Mainly Dry and 01-10 mm. The associated main synoptic features viz., trough at mean sea level, low pressure area, well marked low pressure area, cyclonic storm and cyclonic circulation for each day and their location with respect to the river catchments, viz., over the catchment, neighbourhood of the catchment (within 200 km South or North) and outside the catchment (more than 200 km South or North) have also been studied. The association of AAP ranges over six catchments with different categories of synoptic features has been examined. The distribution of percentage frequency of AAPs associated with the category of synoptic feature for the period 1990 to 2014 has led to development of a Synoptic Analogue Model (SAM) for issue of Quantitative Precipitation Forecast (QPF). The results obtained from SAM have been verified for rainfall data and calculated AAPs of monsoon season of 2015 over all the catchments and different skills scores also presented in this study.