Variation of Zonal Winds in the Upper Troposphere and Lower Stratosphere in Association with Deficient and Excess Indian Summer Monsoon Scenario

Abstract

The Indian summer monsoon is one of the most dominant tropical circulation systems in the general circulation of the atmosphere. The country receives more than 80% of the annual rainfall during a short span of four months (June to September) of the southwest monsoon season. Variability in the quantum of rainfall during the monsoon season has profound impacts on water resources, power generation, agriculture, economics and ecosystems in the country. The inter annual variability of Indian Summer Monsoon Rainfall (ISMR) depends on atmospheric and oceanic conditions prevailed during the season. In this study we have made an attempt to understand the variation of the of zonal winds in the tropical Upper Troposphere and Lower Stratosphere (UT/LS) region during deficient and Excess rainfall years of Indian summer monsoon and its relation to Indian Summer Monsoon Rainfall (ISMR). It is found that in the equatorial Upper Troposphere zonal winds have westerly anomalies during deficient rainfall year’s and easterly anomaly during excess rainfall years of Indian summer monsoon and opposite zonal wind anomaly is noted in the equatorial Lower Stratosphere during the deficient and excess rainfall years of Indian summer monsoon. It is also found that the June to September upper troposphere zonal winds averaged between 15 ° N and 15 ° S latitudes have a long-term trend during 1960 to 1998. Over this period the tropical easterlies and the tropical jet stream have weakened with time.