On the variability of ocean surface current in the Bay of Bengal using self-organizing map (SOM)

The self-organizing map (SOM) is implemented to explore various ocean surface current patterns in the Bay of Bengal (BoB) from 1993 – 2015 based on a satellite sensor-derived current product estimated by combining geostrophic, wind-driven, and temperature-driven current components. Four major patterns/groups corresponding to some of the primary current systems in the BoB are obtained (G1, G2, G3, and G4). The start and end of all the patterns drastically varied year to year and are primarily related to positive and negative Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO) years. The correlation of ENSO and the following year's transition date from WBC to SMC is 0.70, while -0.76 for IOD and transition date from EICC to WMC. Through temporal analysis and monthly frequency of occurrence measurements, this study reveals that the first significant dominant pattern is observed during the summer monsoon season when the southwest monsoon current (SMC) is visible near the south of Sri Lanka (pattern G1). The following major pattern is the winter monsoon current (WMC) in the south of Sri Lanka (pattern G4), whose formation is contributed by the northeast monsoon and westward propagating Rossby wave. The other two dominating patterns are East India Coastal Current (EICC, G2) and Western Boundary Current (WBC, G3). SOM analysis is then performed on WBC with 9 nodes (3×3,namedP1toP9), which captures the meandering nature (P3), and meandering in the presence of SMC (P2), the straight nature (P7) and in the presence of SMC (P4). The spatial and temporal analysis of nine SOM patterns (P1 – P9) suggests that the non-meandering nature of WBC (P4) occurs more frequently than meandering WBC (P2).