Eddy Tracking in the Northwestern Indian Ocean During Southwest Monsoon Regimes

The northwestern Indian Ocean exhibits a relatively highly energetic eddy field during the southwest monsoon season between June and September. This study analyzes the seasonal and interannual variability of the eddy characteristics and their trajectories in the northwestern Indian Ocean using altimetric sea surface height observations from 1993 to 2014. Although the highest number of eddies is found in the Arabian Peninsula coastal region, the strongest eddies, characterized by large radii, amplitudes, and eddy kinetic energies are found along the Somali Current. Trajectories of anticyclonic and cyclonic eddies are investigated to provide insight on the generation and propagation of eddies of varying amplitudes. The largest annual eddy in the Somali Current system corresponds to the Great Whirl, for which the year-to-year variability with respect to shape, size, generation, and propagation was examined, as was the development of these characteristics over the Great Whirl's lifetime. Plain Language Summary The ocean is full of highly energetic quasi-circular features known as mesoscale eddies having typical radii of 10-100 km. Eddies are significant transporters of global heat and ocean characteristics (like salinity and biodiversity). They are best observed by using satellite observations of fluctuations in sea surface height. In this study, we apply an algorithm to sea surface height satellite data in the northwestern Indian Ocean to better understand how and where eddies develop during the summer monsoon season, when eddies are strongest. We determined that though more eddies develop in the northern northwestern Indian Ocean, eddies with largest radii and amplitudes are found along the Somali Current region. These eddies in the Somali Current are also the most energetic, associated with stronger surface currents. The largest eddy observed in the Somali Current during the summer months is referred to as the Great Whirl. This research traces the location where the Great Whirl develops and propagates for each year from 1993 to 2014 and shows significant variability.