A Climatology of the Marine Atmospheric Boundary Layer Over the Southern Ocean From Four Field Campaigns During 2016–2018

Abstract

A climatology of the marine atmospheric boundary layer (MABL) and the lower free troposphere over the Southern Ocean (SO) is constructed using 2,186 high-resolution atmospheric soundings from four recent campaigns conducted in the period of 2016-2018. Relationships between the synoptic meteorology and MABL thermodynamic structure are examined using a k-means cluster analysis, complemented by front and cyclone composite analyses. Seven distinct clusters are identified, five of which are consistent with an established climatology over the SO storm track. Two new clusters (C1 and C2) are introduced over the high-latitude SO. C1 is commonly located poleward of the ocean polar front near mesocyclones, while C2 is located along the Antarctic coastline. A multilayer cloud structure is frequently present in clusters in the vicinity of fronts and cyclones, while a single-layer coverage is more common in a suppressed environment, particularly at lower latitudes. A cloud-free, multilevel inversion is frequently observed in cluster C2, possibly linked to the descending, dry, katabatic winds off the Antarctic coast. A strong, primary inversion is typically present in clusters at lower latitudes with high mean sea level pressure. Across the SO storm track and higher latitudes (cluster C1), a multilevel inversion structure is also commonly observed. A preliminary analysis of two case studies suggests that upper level advection and detrainment of convection associated with mesocyclones are potential drivers of the multilayer cloud coverage over the high-latitude SO rather than the decoupling mechanisms common in the subtropics.

A Characterization of Clouds and Precipitation Over the Southern Ocean From Synoptic to Micro Scales During the CAPRICORN Field Campaigns

“…However, further in-situ data in C2 are needed to confirm the dominance of SLW. This is in sharp contrast to C1, and may be associated with the drying effect of the katabatic winds as discussed in Truong et al (2020). Given that C2 cluster had much fewer soundings from the CAPRICORN experiments, additional data would be beneficial for a better characterization of this environment.…”

“… A conceptual illustration of the seven thermodynamic clusters and their relationships to the extratropical cyclone, cold and warm front, derived in Truong et al. (2020). The red circle indicates the warm cluster (W1), Orange circles the medium clusters (M1–M4), and dark blue circles the cold clusters (C1–C2) and the proximity to Q0.…”

Trends and variability in polar sea ice, global atmospheric circulations, and baroclinicity

“…In particular, the Arctic and the Southern Ocean pose a range of observational and modeling issues. 11,[147][148][149][150][151] These are being addressed in a number of ways and programs.…”

Reanalysis representation of low-level winds in the Antarctic near-coastal region

“…Reduced wind speed correlation coefficients at height, especially in MERRA-2 and JRA-55 during low-wind katabatic states, may be in part related to these temperature biases and in part to the representation of temperature inversions. A dual inversion structure as shown for Mawson and DDU in Figure F1 is common for the Antarctic coastline (Truong et al, 2020) and poses a challenge for faithful representation of near-coastal thermodynamic profiles but its role in the representation of wind profiles warrants further investigation.…”