Spatiotemporal variations of the thermohaline structure and cyclonic response in the northern Bay of Bengal: The evaluation of a global ocean forecasting system

Abstract

Although the performance of the high-resolution global ocean forecasting system, which is based on First Institute of Oceanography surface wave-tide-circulation coupled ocean model (FIO-COM) has been demonstrated to have reasonable accuracy in global context, especially in tropical oceans and some special cases, the assessment needs to be extended in different parts of the global oceans. As such, given the significance of a regional Ocean Forecasting System (OFS) in the world's prominent freshwater dominated basin, the northern Bay of Bengal, a groundwork is crucial for the modeling community. Thus, performance of FIO-COM analysis and forecasting results is assessed by utilizing available moored buoy, satellite, and reanalysis datasets. The present study compares the thermohaline structure related variables (e.g., temperature, salinity) from FIO-COM with aforementioned datasets on a seasonal and daily basis. We focused on evaluating the FIO-COM outputs during a very severe cyclonic storm named Titli that formed in October, 2018. The root-mean-square errors (RMSEs) for sea surface temperature (SST) ranges from 0.47 to 0.71 °C, and for sea surface salinity from 0.62 to 0.83 psu; while vertical profile RMSE ranges from 0.27 to 1.0 °C for temperature, and 0.22 to 0.56 psu for salinity between FIO-COM products and observations. Daily variations in different thermohaline structure related variables at two RAMA positions are also well captured by the FIO-COM outputs. Both model and satellite data show pronounced SST cooling (approximately 2.0–2.5 °C) and increased sea surface salinity (~ 1 psu) on the right side of the cyclone track. High SST, TCHP and deep isothermal layer depth were the main oceanic triggering forces to intensify the cyclone Titli.