The characteristics of the atmospheric boundary layer structure over the Cosmonaut Sea and Bellinsgauzen Sea during summer 2021

Abstract

Atmospheric boundary layer (ABL) structure over the Southern Ocean not only determines air-sea interactions but also influences local synoptic processes. However, due to the scarcity of observations, it has been rarely investigated. Here, based on the radiosonde observations conducted during the 37th Chinese Antarctic Scientific Expedition, the characteristics of the ABL structure over the Cosmonaut Sea and Bellinsgauzen Sea in the 2021 summer are revealed. The main findings are as follows: (1) The mean ABL height (ABLH) is lower in the ice-covered region than in the open water region, as enhanced radiative cooling and weakened sea-air heat exchange suppress the development of ABL. (2) The Thorpe method can well describe the vertical distribution of turbulent dissipation rate (ε) in ABL, and suggests that there is a noticeable difference in the vertical profile of ε between convective boundary layer and near-neutral boundary layer. (3) A case study of the most intense cyclone in January shows that the mean ABLH is higher during the cyclone period than during non-cyclone periods. Cold advection brought by the cyclone destabilizes stable stratification aloft, promoting the coupling of cloud and ABL. Concurrently, the cyclone-driven strong winds enhance low-level jets, intensify vertical shear, and thereby foster turbulent mixing. Together, these mechanisms strengthen turbulent activity and deepen the ABLH during the cyclone period.