Recent changes in the trend, prominent modes, and the interannual variability of Indian summer monsoon rainfall centered on the early twenty-first century
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In this study, the recent changes in rainfall trend, prominent modes, and interannual variability of Indian summer monsoon rainfall (ISMR) for the period 1980–2014 is investigated. Rainfall observations showed a decreasing trend during 1980–2000 (period 1) which changed to a significant increasing mode for the period 2001–2014 (period 2). The analysis shows that two prominent changes in the second period can induce the recent increasing trend of ISMR. The first one is the increased easterly wind anomalies from the equatorial Pacific associated with recent cooling in the eastern Pacific, and the second one is the increased cross-equatorial flow in the Indian Ocean as a result of increased land-sea thermal contrast. During the period 2, the dominant mode of ISMR variability increased and the connection with boundary forcing has intensified. The first mode of ISMR became strongly related to central and east Pacific SST (El Niño Southern Oscillation (ENSO)) anomalies after 2000, while its relationship with major SST indices was weak before that. The second mode contributed to around 14% of variability after the 2000s and is strongly related to Indian Ocean Dipole mode. These modes represent the interannual variability of ISMR during both the periods, and it increases considerably in the second period. Another significant difference between the two periods is that during period 1, many of the severe monsoon events are independent of ENSO; contrary during period 2, many were associated with that. Thus along with the significant change in trend, ISMR has stronger interannual variability, which is the prominent mode of Indian summer monsoon rainfall in the recent period.
Authors acknowledge the Director, IITM for the support. The work is carried out as part of the Master’s dissertation of the first author. Datasets are downloaded from respective websites. Plots are prepared using GrADS software.
IITM is fully funded by the Ministry of Earth Sciences (MoES), Govt. of India.
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