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Intraseasonal variability of the upper ocean in the Seycelles-Chagos Thermocline Ridge Region and its impact on MJO initiation and development

The Seycelles-Chagos Thermocline Ridge (SCTR) is a zonally oriented shallow ridge– like feature in the thermocline of the southern tropical Indian Ocean centered around 8!S. The shallow thermocline and mixed layer makes the region favorable to strong air– sea interactions. Indeed longer period (50-100 days) Madden Julian Oscillation events (MJOs) are centered near 8!S with strong signatures in the intraseasonal variability of outward longwave radiation (OLR) and sea surface temperature (SST) in the austral summer. Scale interactions link the diurnal cycle, MJO activity and interannual variability (the Indian Ocean Dipole, IOD, and ENSO). Air/sea fluxes of heat, lateral advection by ocean currents, and turbulent mixing all play a role in changing the SST which in turn affects atmospheric convection. Understanding the controlling factors on SST variability in the SCTR region and how this feeds back to MJO initiation and development is the primary goal of this proposal.

As part of the international program CINDY/DYNAMO intense oceanic and atmospheric measurements were taken from the R/V Mirai over a two month period (Oct.– Nov., 2011) within the SCTR region at 8!S, 80.5!E. The data will be used to estimate the impact of individual processes on the SST and upper ocean heat content, including vertical ocean mixing, diurnal variations, heat and freshwater fluxes, the radiation of near-inertial waves, and lateral advection (when combined with satellite and RAMA mooring data). A suite of models will be used to complement the results based on observations and to extend the analysis both spatially and in time. Numerical experimentation with a regional coupled model of the Indian Ocean will be used to assess the impact of upper ocean processes on the coupling between ocean and atmosphere and the evolution of MJO events. The expected outcomes include: (a) the determination of the factors controlling the SST and upper ocean heat content in the SCTR region before, during and after the development of an MJO event, (b) an evaluation of the representativeness of the ocean response to MJO events observed during the DYNAMO period, and (c) a determination of the impact of the presence of the thermocline ridge, surface fluxes (in particular precipitation) and associated upper ocean variability on the initiation and development of MJO events.

The potential of improving the simulation and prediction of MJO in models, and the associated societal benefits, underlie the goals of this proposal. This also applies to assessing the changes to MJO activity, and its impact on the monsoons and tropical cyclones, brought about by climate change. As such the proposal is aligned with the first of the five–year climate objectives outlined in NOAA’s Next Generation Strategic Plan (NGSP), namely: Improved scientific understanding of the changing climate system and its impacts. The proposal is directly related to area (1) of the NOAA Climate Program Office Earth System Science 2013 call: Understanding and Improving Prediction of Tropical Convection Using Results from the DYNAMO Field Campaign.

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