July droughts over Homogeneous Indian Monsoon region and Indian Ocean dipole during El Nino events

The monthly summer monsoon rainfall over the Homogeneous Indian Monsoon region (HI) that represents most of the variance of all-India monsoon rainfall is investigated using observational data from 1880 to 2002. Severe droughts in July occur mostly during El Nino events of the boreal summer monsoon season. They occurred frequently in the late 19th to early 20th century, rarely in the middle of the 20th century, and again occasionally occurred after the 1960s. During El Nino events, severe droughts in July over HI are significantly associated with smaller sea surface temperature-(SST) based Indian Ocean Dipole mode index (SSTDMI) in May and July compared to the years without these outstanding events. The evolution of SSTDMI that usually starts around May/June during Et Nino events tends to delay when July precipitation over HI is abnormally low. Nino3 values from May through October are not significantly associated with severe droughts over HI in July during El Nino events indicating that the strength of El Nino events is not related to the occurrences of severe droughts in July. Copyright (c) 2008 Royal Meteorological Society