Wet and dry years of Indian summer monsoon and its relation with Indo-Pacific sea surface temperatures


H. Varikoden, Indian Institute of Tropical Meteorology, Dr. Homi Bhabha Road, Pashan, Pune-08, India. E-mail: hamza@tropmet.res.in


Regional characteristics of Indian Summer Monsoon Rainfall (ISMR) during dry and wet monsoon years associated with El Niño Southern Oscillation (ENSO) and non-ENSO (normal) periods are investigated. Four cases such as wet monsoon years associated with ENSO (EW) and non-ENSO (NW) events and dry monsoon years associated with ENSO (ED) and non-ENSO (ND) events have been discussed. The dry and wet years associated with ENSO and non-ENSO periods show significant differences in the spatial pattern of rainfall. During wet years (EW and NW), the rainfall is abnormally high in the west coastal stations. However, during EW years, anomalous heavy rainfall is observed in the northern part of the west coast while during the NW years, the rainfall is high in southwest coastal regions. In central India, the rainfall is abnormally high only during the wet years associated with non-ENSO events (NW). The west coastal areas receive below normal rainfall during ED, ND years, however, the negative anomalies are large during ED years compared to ND years. The low level (1000 hPa) moisture transport is coherent with the changes in the spatial patter of ISMR. The Indo-Pacific sea surface temperatures (SSTs), low level circulation (at 850 hPa) features and general circulation associated with the four cases of ISMR have also been studied in detail. During wet phases of ISMR, the SST over the pacific ocean is abnormally cool and that during dry phases of ISMR is abnormally warm. However, the areas of cool and warm are different during ENSO and normal years. Copyright © 2012 Royal Meteorological Society