472 Linkage between Seasonal Seychelles-Chagos Thermocline Ridge and MJO formation

Monday, 11 January 2016
Subrahmanyam Bulusu, University of South Carolina, Columbia, SC; and J. D'Addezio

Previous research has shown that MJO impacts the Seychelles-Chagos thermocline ridge, SCTR, (55E-65E, 5S-12S) located in the southwest tropical Indian Ocean (SWTIO), but no one has investigated the possibility of SWTIO internal air-sea dynamics producing MJO events on a seasonal or interannual basis. For the first time we demonstrate that SWTIO near surface heat build up and barrier layer formation in boreal fall can produce seasonal MJO events. We utilize salinity from the NASA's Aquarius/SAC-D and ESA's Soil Moisture and Ocean Salinity (SMOS) satellite missions to successfully observe the MJO that forms within the SWTIO as well as the propagating barrier layer that follows in its wake. The eastward propagating barrier layer is caused by both an equatorially trapped downwelling Kelvin wave and anomalous precipitation both of which are consequences of the active phase of the MJO. The Kelvin wave suppresses the thermocline and thus the isothermal layer, while low surface salinity due to precipitation keeps the mixed layer shallow. Aquarius salinity mission gives the most complete representation of the dynamics involved by resolving the shallow mixed layer induced by high near surface salinity stratification. However, Argo and SMOS do not observe the shallower mixed layer and therefore miss critical dynamics associated with air-sea interactions. Because of the location and time of year in which this phenomenon occurs, seasonal MJO genesis within the SWTIO likely plays an important role in Australian monsoon interannual variability. Finally, critical information on salinity stratification in the SWTIO is being left out of widely used model and reanalysis simulations, which is likely one of many reasons why MJO forecasting is still inadequate after decades of research work. Including this new information in forecasting efforts will likely yield better outcomes for annual monsoon prediction.
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