Weather and Climate Extremes (Dec 2021)
Is the Indian monsoon rainfall linked to the Southern Ocean sea ice conditions?
Abstract
In the background of global warming, the necessity for finding a new predictor of Indian summer monsoon rainfall (ISMR) is realised recently as the relationship between the ISMR and the predictive physical parameters keeps changing both in space and time. We developed a linkage between the satellite-derived sea ice over the Southern Ocean and ISMR through the interaction of physical processes occurring between the cryosphere, hydrosphere, and atmospheric environment. The statistical and possible physical linkage were explored using consistent and reliable 38-year time series observations. Lead-lag cross correlation indicated a significant relationship between Southern Ocean sea ice (SOSI) extent and ISMR over the Bellingshausen–Amundsen Sea (BAS). The most significant relationship was obtained in austral autumn (r = −0.5, p < 0.05) with no time lag. We analysed atmospheric circulation pattern over the BAS and Ross Sea corresponding to extreme rainfall events. Excess (deficit) rainfall years showed anomalous cyclonic (anticyclonic) wind patterns that led to anomalous positive (negative) air temperature that facilitated anomalous negative (positive) sea ice conditions in BAS. Hence, the excess rainfall (deficit) events were observed corresponding to a large negative (positive) anomalous sea ice condition in the BAS. This linkage likely occurred through El Niño–Southern Oscillation (ENSO) associated sea surface temperature (SST) variability. To find out the dominant mode of variability and common frequency distribution in the SOSI extent, Niño3.4 SST and ISMR, we have performed the wavelet analysis for exploring the coherence between the respective variables. The spectral analysis showed that both the SOSI extent and ISMR have dominant oscillations in 2–8 years frequency bands similar to the ENSO variability. This observed relationship can be used as the input for future works for physically linking the BAS sea ice condition with the ISMR through the dynamic and thermodynamic ocean-atmospheric components.
