Interdecadal Changes in the ENSO–Monsoon System

Interdecadal Changes in the ENSO–Monsoon System

AUGUST 1999 | CHRISTOPHER TORRENCE, PETER J. WEBSTER
The paper examines the significant interdecadal changes in variance and coherency between the El Niño-Southern Oscillation (ENSO) and the Indian monsoon over the past 125 years. Wavelet analysis is applied to sea surface temperature (Niño3 SST), the Southern Oscillation index (SOI), and all-India rainfall. The results show that there are three distinct time intervals: 1875-1920, 1920-1960, and 1960-present, with high and low variance in ENSO-monsoon interactions. The 12-20-year modulation of ENSO and monsoon amplitudes is also identified. The annual-cycle variance of Niño3 SST and Indian rainfall is negatively correlated with interannual ENSO signals, suggesting a transfer of energy between the annual cycle and ENSO on interdecadal timescales. Wavelet coherency analysis reveals high coherence between Niño3 SST and Indian rainfall during high variance intervals, indicating clear ENSO-monsoon relationships. The findings are robust across different datasets and analysis methods, suggesting that these changes may be part of the internal variability of the tropical climate system or influenced by external factors.The paper examines the significant interdecadal changes in variance and coherency between the El Niño-Southern Oscillation (ENSO) and the Indian monsoon over the past 125 years. Wavelet analysis is applied to sea surface temperature (Niño3 SST), the Southern Oscillation index (SOI), and all-India rainfall. The results show that there are three distinct time intervals: 1875-1920, 1920-1960, and 1960-present, with high and low variance in ENSO-monsoon interactions. The 12-20-year modulation of ENSO and monsoon amplitudes is also identified. The annual-cycle variance of Niño3 SST and Indian rainfall is negatively correlated with interannual ENSO signals, suggesting a transfer of energy between the annual cycle and ENSO on interdecadal timescales. Wavelet coherency analysis reveals high coherence between Niño3 SST and Indian rainfall during high variance intervals, indicating clear ENSO-monsoon relationships. The findings are robust across different datasets and analysis methods, suggesting that these changes may be part of the internal variability of the tropical climate system or influenced by external factors.
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Understanding Interdecadal changes in the ENSO-monsoon system