Abstract
AbstractThe positive Indian Ocean Dipole (IOD) event in 2019 was among the strongest on record, while the Indian Summer monsoon (ISM) was anomalously dry in June then very wet by September. We investigated the relationships between the IOD, Pacific sea surface temperature (SST), and ISM rainfall during 2019 with an atmospheric general circulation model forced by observed SST anomalies. The results show that the extremely positive IOD was conducive to a wetter‐than‐normal ISM, especially late in the season when the IOD strengthened and was associated with anomalous low‐level divergence over the eastern equatorial Indian Ocean and convergence over India. However, a warm SST anomaly in the central equatorial Pacific contributed to low‐level divergence and decreased rainfall over India in June. These results help to better understand the influence of the tropical SST anomalies on the seasonal evolution of ISM rainfall during extreme IOD events.
Highlights
The Indian Ocean Dipole (IOD) is one of the dominant modes of variability of the tropical Indian Ocean which was discovered and named at the end of the 1990s (Saji et al, 1999; Webster et al, 1999)
We investigated the relationships between the IOD, Pacific sea surface temperature (SST), and Indian Summer monsoon (ISM) rainfall during 2019 with an atmospheric general circulation model forced by observed SST anomalies
The results show that the extremely positive IOD was conducive to a wetter-than-normal ISM, especially late in the season when the IOD strengthened and was associated with anomalous low-level divergence over the eastern equatorial Indian Ocean and convergence over India
Summary
The Indian Ocean Dipole (IOD) is one of the dominant modes of variability of the tropical Indian Ocean which was discovered and named at the end of the 1990s (Saji et al, 1999; Webster et al, 1999). The mean structure of moisture convergence and meridional specific humidity distribution undergoes significant changes in contrasting IOD years, which in turn influences the meridional propagation of BSISO and the related precipitation anomalies over India (Ajayamohan et al, 2008; Kikuchi et al, 2012; Konda & Vissa, 2019; Singh & Dasgupta, 2017). At this timescale, the ocean-atmosphere dynamical coupling has been found to be important to the extended Indian summer monsoon break of July 2002 (e.g., Krishnan et al, 2006).
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