Atmospheric Hydrology of the Anomalous 2002 Indian Summer Monsoon

Abstract

The 2002 Indian summer monsoon season is unique because of its exceptional weakness, its association with a relatively weak El Niño, and its precedence by over a decade in which ENSO events fail to be associated with significant monsoon anomalies. In this study, atmospheric hydrology during the 2002 summer monsoon and its relationship to monsoon seasons accompanying El Niño events since 1948 are assessed using reanalysis and satellite fields. Strong hydrologic deficits are identified for July and September 2002. During July, the impact of the disturbed Hadley and Walker circulations in the African and Indian Ocean region on vertically integrated moisture transport (VIMT) in the Arabian Sea and India is found to be key to the Indian drought. Interhemispheric coherence in satellite-derived surface wind anomalies is also identified. During September, VIMT and surface wind anomalies, both to the east and west of India, contribute to anomalous moisture divergence in India. Bay of Bengal SST and Indian CAPE anomalies are found to act in response to the season?s major break episodes, contrary to other studies that suggest their role as instigators of break periods. The 2002 season is also found to exhibit characteristics that are common to other recent weak monsoons accompanying El Niño, such as strong westerly VIMT anomalies in the western Pacific Ocean and easterly VIMT anomalies in the Arabian Sea. Hydrologic anomalies that distinguish many recent normal monsoon seasons coinciding with El Niño from the El Niño distribution overall are not evident in 2002. In many respects, the 2002 season thus represents a reemergence of the hydrologic anomalies that have accompanied a strong monsoon?ENSO teleconnection over the past 50 yr and may present a challenge for perspectives that suggest a lasting decoupling of the monsoon?ENSO systems.