Gopalakrishnan, G., A. C. Subramanian, A. J. Miller, H. Seo and D. Sengupta, 2019:

Estimation and prediction of the upper ocean circulation in the Bay of Bengal.

Deep-Sea Research II, sub judice.

Abstract. The upper ocean stratification and circulation in the Bay of Bengal (BoB) plays a key role in the northward propagating monsoon intraseasonal oscillation during the months of June – August. This region is highly influenced by the strong, seasonal atmospheric forcing and the oceanic circulation is characterized by dominant mesoscale variability and strong gradients in salinity and temperature during the monsoon period. Given the key role of the BoB ocean state in the monsoon circulation, it is important to produce an accurate state estimate of the BoB ocean circulation. Hence, we use a high-resolution, regional implementation of Massachusetts Institute of Technology general circulation model (MITgcm) and its adjoint-based four-dimensional variational (4DVAR) system to assimilate satellite-derived Sea Surface Height (SSH) and Sea Surface Temperature (SST) data in the BoB for a period of one month (June 1 – 30, 2017). It is shown that the MITgcm-4DVAR assimilation system is able to significantly improve the model consistency with the assimilated observations in the BoB region. The state estimation reduced the model-data misfit by 50% and provided a reasonably accurate and dynamically-consistent BoB ocean circulation for the one-month hindcast period. We further tested the state estimate by performing forecasting experiments using optimized solutions to initialize the forecast for a period of 30-days (July 1 – 30, 2017) from the end of the hindcast period. These forecasts used either atmosphere reanalysis and ocean analysis forcings or monthly climatology of atmosphere reanalysis and ocean analysis forcings, therefore do not represent a “true” regional ocean forecast forced using actual atmosphere and ocean forecasts. The model forecast cross-validation showed that the initial conditions from the state estimate improves the prediction of sea surface state in the BoB. The model hindcast and forecast were also cross-validated with independent, three-dimensional Argo temperature and salinity observations in the BoB. Additional state estimation experiments for other periods showed similar model performance with improved hindcasts and forecasts for the BoB region.

Preprint (pdf)