Recent changes in the major modes of Asian summer monsoon rainfall: influence of ENSO-IOD relationship

• Published in: Theoretical and applied climatology 2021-02, Vol.143 (3-4), p.869-881
• Main Authors: Pillai, Prasanth A, Ramu, D. A., Nair, Ravikumar C
• Format: Article
• Language: English
• Subjects: Analysis; Anomalies; Aquatic Pollution; Atmospheric Protection/Air Quality Control/Air Pollution; Atmospheric Sciences; Climate science; Climatology; Decay; Dipoles; Earth and Environmental Science; Earth Sciences; El Nino; El Nino phenomena; El Nino-Southern Oscillation event; El Nino-Southern Oscillation event-rainfall relationships; Flavors; Interannual variability; Monsoon circulation; Monsoon rainfall; Monsoons; Oceans; Original Paper; Precipitation variability; Rain; Rain and rainfall; Rainfall; Rainfall variability; Sea surface; Sea surface temperature; Sea surface temperature anomalies; Southern Oscillation; Summer; Summer monsoon; Surface temperature; Tropical circulation; Tropical climate; Tropical environments; Variability; Waste Water Technology; Water Management; Water Pollution Control; Wind
• ISSN: 0177-798X; 1434-4483
• DOI: 10.1007/s00704-020-03454-3

Indo-Pacific Ocean sea surface temperature (SST) anomalies in the form of Indian Ocean Dipole (IOD) and El Niño-Southern Oscillation (ENSO) have a major role in determining the climate of the tropics and extratropics. The tropical Pacific variability was dominated by canonical ENSO (EOF1) and El Niño Modoki (EOF2) during the 1980–1998 period (period 1), while during the 1999–2017 period (period 2), both the flavors of ENSO contributed to EOF1. This Pacific Ocean variability weakened the ENSO-IOD relationship also. The present study estimates the changes that occurred to the major modes of Asian summer monsoon (ASM) rainfall during these two periods and addresses the role of the recent changes in SST boundary forcing in ASM interannual variability. During period 1, the first mode (EOF1) of ASM rainfall was associated with ENSO and IOD with 32% variability. But after 1998, EOF1 depends only on the ENSO flavors (canonical and Modoki ENSO) and has slightly reduced variability (26%). The second mode was controlled by the decay phase of ENSO during the 1980–1998 period (12%), while the eastern Indian Ocean and central-northeast Pacific SST variability contributed to EOF2 (15%) during period 2. EOF3 is controlled by IOD in both periods. Further analysis indicates that the extended warming pattern from central to eastern Pacific of ENSO during period 2 weakened ENSO-IOD co-occurrence through the modification of tropical circulation. In the absence of IOD, ENSO-monsoon teleconnection becomes stronger during period 2 than in the previous period. Indian summer monsoon rainfall (ISMR) relationship with the developing phase of ENSO became stronger after 1998, and that of the decay phase of ENSO is decreased. The ISMR-ENSO Modoki relationship has a phase shift from summer maxima to winter maxima. Meanwhile, the ISMR-IOD relationship in the absence of ENSO became slightly stronger in the 1999–2017 period. Thus, the Pacific variability in these two periods influenced ASM rainfall variability through the modulation of its relationship with tropical Indo-Pacific SST anomalies.