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Data

Gridded wind (both u and v) and temperature data with a horizontal resolution of 2.5º lat x 2.5º lon are available for 17 levels, from surface to 10 hPa in the NCEP/NCAR reanalysis data set (Kalnay et al, 1996). Monthly mean values of wind at 300, 200, 150, 100, 70, 50, 30, 20 and 10 hPa levels for the period 1979-1994 are used for the present analysis. Temperature data at all the 17 levels have been analysed to understand the tropopause break. Gridded monthly mean total ozone data (version 7) measured by the TOMS instrument onboard Nimbus-7 spacecraft is used for the ozone analysis (Stanford et al, 1995). This data set has 1º lat x 1.25° lon spatial resolution and covers the period November 1978 to April 1993.

Indian summer monsoon rainfall data has been taken from Parthasarathy et al (1994). ISMR is the area weighted average June to September rainfall of 306 stations well distributed over India. The long period average ISMR is 852.4 mm and its standard deviation is 84.69 mm. Table 1. gives the ISMR for the 1979-93 period. The 3 dry years are the years of maximum rainfall deficiency while the 3 wet years are the years of maximum rainfall excess. During the study period 1979-1993 the years 1979, 1982 and 1987 are dry monsoon years and 1983, 1988 and 1990 are wet monsoon years. All these years have rainfall excess/deficiency more than one standard deviation from the long period average except 1990 (Table.1).

                               Table.1  Indian Summer Monsoon Rainfall (mm) (Parthasarathy et al 1994)