SMAP Salinity Observations Detect Indian Monsoon Intraseasonal Oscillations
[14-Dec-2018] Bulusu, S.
Presented at the 2018 AGU Fall Meeting
Indian Southwest monsoon (or Summer monsoon) has strong intraseasonal oscillations in the form of active and break spells of monsoon rainfall within the monsoon season. These Intraseasonal oscillations (ISOs) are a critical driver of air-sea fluxes in the Indian Ocean. The impacts of ISOs at three major periodicities (30-90 days, 10-20 days, and synoptic 3-7 day periods) were investigated using satellite-derived estimates of sea surface salinity (SSS) from NASA's Soil Moisture Active Passive (SMAP) mission. The 30-90 day signal corresponds with the Madden-Julian Oscillation (MJO) events, which induce eastward- and northward-propagating oscillations between active and break spells. The quasi-biweekly 10-20 day signal signifies a westward-propagating atmospheric double-cell system (either two highs or two lows) centered about 15-20° N and the equator. Oscillations in the monsoon trough are responsible for the 3-7 day synoptic signal. Similar results were found in the salinity of the Climate Forecast System version 2 (CFSv2) salinity, though CFSv2 underestimated the amplitude of ISOs due to an underestimation of freshwater flux. A uniform signal between the 10-20 day signal of SMAP salinity, E-P, and OLR was found. The 10-20 day and 3-7 day ISOs showed a strong response to seasonality, peaking in amplitude before and after the summer monsoon season.