Association between extreme monsoons and the dipole mode over the Indian subcontinent

The relationship of summer monsoon over India with the Indian Ocean Dipole Mode has been investigated applying simple statistical techniques. While a long time series of 132 years based on 1871-2002 for both summer monsoon rainfall as well as dipole mode index has been used in this study, the NCEP-NCAR reanalysis data (1948-2002) are used to examine the circulation features associated with the extreme dipole and monsoon phases. These flow patterns bring out the dynamics of the dipole - monsoon relationship. Lead/lag correlations between the dipole mode index and the Indian monsoon rainfall are computed. Results reveal that numerically the relationship is stronger following the monsoon. The lower troposphere flow patterns at 850-hPa associated with the extreme phases of the dipole and monsoon are consistent with the correlation analysis. Further a strong (weak) summer monsoon favours the development of the negative (positive) dipole event in autumn. The sliding correlations between Indian monsoon rainfall and the dipole mode index suggest that the impact of monsoon over dipole is weakening after 1960s. This weakening relationship has been evidenced by the composites of sea-surface temperature anomalies and circulation patterns. All the above analysis suggests that the summer monsoon has more influence on the dipole mode than vice-a-versa