July droughts over Homogeneous Indian Monsoon region and Indian Ocean dipole during El Niño 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 Niño 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 Niño 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 El Niño events tends to delay when July precipitation over HI is abnormally low. Niño3 values from May through October are not significantly associated with severe droughts over HI in July during El Niño events indicating that the strength of El Niño events is not related to the occurrences of severe droughts in July. Copyright  2008 Royal Meteorological Society