Nonstationarity and potential multi-decadal variability in Indian Summer Monsoon Rainfall and Southern Annular Mode teleconnection

While the El Nino-Southern Oscillation and Indian Summer Monsoon Rainfall (ISMR) relationship is weak in recent years, a strong correlation between May Southern Annular Mode Index (SAMI) and June-July (JJ) ISMR is a southern hemispheric source of ISMR predictability. Here, using observed and reanalysis data, we find that the SAMI-ISMR relationship is non-stationary with a potential multi-decadal variability. Both during high/low correlation periods (1980-2010)/(1949-1979), a Southern Indian Ocean Dipole (SIOD) pattern of JJ sea surface temperature anomaly is found to reverse sign during strong and weak SAMI years. The changes in the strength and location of the northern pole of SIOD during the two time blocks are consistent with corresponding changes in the cross equatorial flow and monsoon south-westerlies together with change in SAMI-ISMR correlations. Our analysis indicates teleconnection pathways through which the Atlantic Multidecadal Oscillation (AMO) may be responsible for the multi-decadal swings of SAMI-ISMR correlations through modulation of the SIOD.

Automated summary

This study found that the relationship between the Southern Annular Mode Index (SAMI) and Indian Summer Monsoon Rainfall (ISMR) is non-stationary and may have multi-decadal variability. However, there is a strong correlation between SAMI and June-July ISMR, which is linked to sea surface temperature anomalies in the Southern Hemisphere.