Understanding of anomalous Indian Summer Monsoon rainfall of 2002 and 1994

This study focuses on understanding of the deficient rainfall of 2002 and excess rainfall of 1994 of the Indian Summer Monsoon and its association with large-scale circulation features. Outgoing longwave radiation (OLR) and 200 hPa flow regimes have been compared during a deficient year (2002) with those during an excess rain year (1994) for the northern summer months. The main emphasis is on the month of July (2002) when rainfall was the lowest during the past 100 years. Positive OLR anomalies of substantial magnitude are prominent over large parts of the Indian Ocean, Arabian Sea, most parts of India. Negative OLR anomalies prevailed over the north Pacific in July 2002. These positive OLR anomalies during the deficient Summer Monsoon of 2002 indicate very weak convection over the Indian subcontinent. The opposite patterns of OLR anomalies are found in the excess rain monsoon of 1994. Examination of upper tropospheric (200 hPa) circulation fields indicates significant changes in velocity potential, stream function, and geopotential height anomalies during 2002 and 1994. The field of geopotential height anomalies shows cyclonic (anticyclonic) anomalous circulation developed over the Caspian Sea near central Asia during 2002 (1994) rain years. The upper level stream function anomalies show weak (strong) upper level high in 2002 (1994) over large parts of India and surrounding areas in July.