Observations of Variations in Atmospheric Boundary Layer and Stratocumulus over a Mesoscale Warm Eddy in the Kuroshio Extension

A research vessel sailed across a warm eddy in the Kuroshio Extension (KE) on 13 April 2016(Fig. 1), and captured an abrupt development of stratocumulus (Fig. 2) under a synoptic high pressure. Over the ocean eddy, the increases in surface heat flux lowered surface pressure, which accelerated southeasterly winds. The southeasterly winds transported moisture toward the low pressure and enhanced the air-sea interface heat flux, which in turn deepens the low pressure. This warm eddy effect lowered the lifting condensation level (LCL) and aided the development of the stratocumulus. The results from a regional atmospheric model simulation confirm the warm eddy effect on the marine atmospheric boundary layer (MABL) and stratocumulus (Fig. 3(a)). Over the warm eddy, low-level convergence developed and the resultant rising motion deepened the MABL, allowing stratocumulus to develop. Further experiments show that sea surface temperature anomalies of the warm eddy account for 80% of the updraft and 95% of cloud water mixing ratio (Fig. 3(b)). The synthesis of in-situ soundings and modeling contributes to understanding the mechanism of the MABL and marine stratocumulus response to ocean eddies.