An Intrathermocline Eddy Observed in the Northeastern Bay of Bengal

Abstract

An intrathermocline eddy (ITE) was detected to the northwest of Preparis Channel by in situ measurements in January 2018. The ITE had a horizontal extent of approximately 200 km and a maximum velocity of approximately 60 cm/s at core depths between 75 and 130 m. This ITE was generated by the transformation from a preexisting surface-intensified anticyclonic eddy (SAE). The blocking of the northeast monsoon by the Arakan Yoma Mountains resulted in a weak wind stress on the leeward side of the mountains. This caused positive Ekman pumping around Preparis Channel together with eddy wind-driven upwelling, shoaling the upper thermocline in the SAE, and thus turning it into an ITE. Among the 71 anticyclonic eddies detected by Argo profiles around Preparis Channel from 2003 to 2018, approximately 60% were ITEs, indicating that Preparis Channel could be the main source for ITE generation in Bay of Bengal.