On the Recent Change of the Indian Summer Monsoon-ENSO Relationship

A remarkable change in the relationship between the El Niño-Southern Oscillation (ENSO) and Indian summer monsoon (ISM) during the last five decades is examined using a fine resolution rainfall data set, ENSO indices and a large-scale monsoon circulation index. Although the all-India monsoon rainfall (IMR) index represents rainfall variations particularly over central and western parts of India, it does not represent rainfall variability in northeast India, which leads to the weakening correlation between IMR and the large-scale monsoon index in recent decades. The relationship between ISM and ENSO was strong in late summer over central and northwest India before the late 1970s but, after the late 1970s, the strongest relationship between ISM and ENSO shifted to early summer and also moved to over northeast India. In effect, the recent weakening relationship between ISM and ENSO based on the use of IMR represents a change in dominance of the spatial correlation pattern, from northwest-central parts to northeast part after the late 1970s.