1997: The El Niño of the Century and the Response of the Indian Summer Monsoon

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Abstract
The year 1997 was characterized by the rapid development of an El Niño whose strength exceeded any previously observed this century. The basic understanding of the influence of El Niño on the Asian summer monsoon suggested that the monsoon should be substantially deficient, yet the all-India rainfall (AIR) was 2% above normal. The reasons for this have been investigated in terms of both the seasonal-mean, large-scale circulation anomalies and the subseasonal, regional weather events. By comparing the results with a similar analysis of two previous major El Niño events in 1982 and 1987, the common and disparate features of the response have been identified. On the large scale, the basic hypothesis that, in El Niño years, the strength of the monsoon is influenced by a modulation of the Walker circulation, in which there is implied additional subsidence over the west Pacific and southeast Asia, is generally supported by the results. However, the results have shown that the modulation of the local Ha... Abstract The year 1997 was characterized by the rapid development of an El Niño whose strength exceeded any previously observed this century. The basic understanding of the influence of El Niño on the Asian summer monsoon suggested that the monsoon should be substantially deficient, yet the all-India rainfall (AIR) was 2% above normal. The reasons for this have been investigated in terms of both the seasonal-mean, large-scale circulation anomalies and the subseasonal, regional weather events. By comparing the results with a similar analysis of two previous major El Niño events in 1982 and 1987, the common and disparate features of the response have been identified. On the large scale, the basic hypothesis that, in El Niño years, the strength of the monsoon is influenced by a modulation of the Walker circulation, in which there is implied additional subsidence over the west Pacific and southeast Asia, is generally supported by the results. However, the results have shown that the modulation of the local Ha...

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