Monitoring Intraseasonal Oscillations in the Indian Ocean Using Satellite Observations

Intraseasonal oscillations (ISOs) in the Indian Ocean play a significant role in determining the active (wet) and break (dry) cycles of the southwest monsoon rainfall. In this study, we use satellite-derived precipitation, sea level anomalies (SLAs), sea surface salinity (SSS), sea surface temperature, and surface winds to monitor the 30-90-day, 10-20-day, and 3-7-day ISOs, and how they influence local dynamics. The main focus of this work, however, is showing the importance of using SLA and SSS to monitor ISOs. Mixed Rossby gravity waves were found to induce convection associated with the southern cell of the 10-20-day mode, with surface winds from the northern cell modulating coastal Kelvin waves in the Bay of Bengal. The 10-20-day SSS response is instead more closely related to wind-induced upwelling in the central Bay of Bengal and river runoff in the northern Bay. The 3-7-day mode was found to have a weak oceanic signal, as the monsoon trough is mainly positioned over land, though SSS captured the structure of the signal most clearly. This study highlights the need for high spatial resolution SLA in order to adequately capture 3-7-day oscillations in the monsoon trough.