Air–Sea Interactions during Indian Ocean Monsoon Intraseasonal Oscillations

Monsoon Intraseasonal Oscillations (MISO) are a part of the energetic boreal-summer sub-seasonal (20 to 60 day) variability in the northern Indian Ocean (IO). MISO events appear to originate just south of the equator, and propagate northward into the Bay of Bengal (BOB) while taking a westward turn in the northern BOB. MISO’s are characterized by alternative active (moist convection) and break/dry periods, and the predictability of such phases are frequently noted to be unreliable. It has been pointed out that inclusion of air-sea coupling during the MISO events are essential for high fidelity predictions, especially the MISO propagation and precipitation. A two-month (June 3 to July 20, 2018) comprehensive field study entitled MISO-BOB was conducted in the BOB to investigate the structure and dynamics of MISO events. The US research vessel Tommy G. Thompson and a C-130 aircraft from ‘Hurricane Hunters’ were the major platforms, the latter being deployed for a two-week period. An array of in-situ and remote sensors were used on these platforms to collect data on oceanic and atmospheric variables. The locations for atmospheric data acquisition were selected using satellite derived products from JAXA GSMap, CIMSS and IMD as well as weather forecasts of global climate models and mesoscale models such as GFS and WRF produced by IMD. Northward propagating coherent signals of sea surface temperature (SST), heat, momentum and moisture fluxes, outgoing longwave radiation (OLR) and rainfall anomalies from satellite and ship/aircraft sensors were collected and analyzed to understand the role of air-sea coupling and atmospheric internal dynamics that drive the formation, propagation and westward directional shift of MISO. This presentation deals with a synthesis based on initial campaign-data analysis as well satellite and reanalysis information.