Detecting Monsoon Intraseasonal Oscillations in the Indian Ocean in Salinity

Monsoon intraseasonal oscillations (ISOs) significantly influence the variability and strength of precipitation associated with the southwest monsoon and have a profound impact on air-sea interactions and mixed layer dynamics in the Indian Ocean. Northward-propagating ISOs contribute to an increase in momentum and moisture from the tropical Indian Ocean to the Indian subcontinent that intensifies monsoonal rainfall rates. The atmospheric systems associated with ISOs induce circulation shifts that directly impact the strength and timing of active and break monsoon periods, which are respectively characterized by wet and dry conditions. These patterns can be easily translated into the ocean through sea surface salinity (SSS), as salinity is highly dependent on precipitation. This research explores the variability of the southwest monsoon over multiple ISO periods in order to properly identify the individual contributions of the MJO (30-90-day), quasi-biweekly oscillations (10-20-day) and synoptic events from oscillations in the monsoon trough (3-7-day). This works uses satellite-derived salinity from SMAP, Aquarius, SMOS to find that the SSS response to the 30-90-day atmospheric signal propagates northward following the northward propagation of convection and precipitation in the Bay of Bengal (BoB). 10-20-day SSS signals are in response to upwelling in the central BoB but deviate in the northern BoB where riverine input overwhelms the signal. 3-7-day SSS signals are heavily influenced by synoptic weather and tropical systems. In this study, we compare the different satellite salinity products and their associated processing algorithms (combined active passive; CAP vs non-CAP) in order to determine which product most adequately captures the ISO signals in SSS. We find that the best salinity product is SMAP CAP, and that the CAP algorithm increases signal robustness, has higher spatiotemporal resolution, and can reach closer to coastlines.