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Journal Article
Liu, JW, Xie SP, Norris JR, Zhang SP.  2014.  Low-level cloud response to the Gulf Stream front in winter using CALIPSO. Journal of Climate. 27:4421-4432.   10.1175/jcli-d-13-00469.1   AbstractWebsite

A sharp sea surface temperature front develops between the warm water of the Gulf Stream and cold continental shelf water in boreal winter. This front has a substantial impact on the marine boundary layer. The present study analyzes and synthesizes satellite observations and reanalysis data to examine how the sea surface temperature front influences the three-dimensional structure of low-level clouds. The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite captures a sharp low-level cloud transition across the Gulf Stream front, a structure frequently observed under the northerly condition. Low-level cloud top (<4 km) increases by about 500 m from the cold to the warm flank of the front. The sea surface temperature front induces a secondary low-level circulation through sea level pressure adjustment with ascending motion over the warm water and descending motion over cold water. The secondary circulation further contributes to the cross-frontal transition of low-level clouds. Composite analysis shows that surface meridional advection over the front plays an important role in the development of the marine atmospheric boundary layer and low-level clouds. Under cold northerly advection over the Gulf Stream front, strong near-surface instability leads to a well-mixed boundary layer over the Gulf Stream, causing southward deepening of low-level clouds across the sea surface temperature front. Moreover, the front affects the freezing level by transferring heat to the atmosphere and therefore influences the cross-frontal variation of the cloud phase.

Liu, W, Lu J, Xie SP, Fedorov A.  2018.  Southern Ocean heat uptake, redistribution, and storage in a warming climate: The role of meridional overturning circulation. Journal of Climate. 31:4727-4743.   10.1175/jcli-d-17-0761.1   AbstractWebsite

Climate models show that most of the anthropogenic heat resulting from increased atmospheric CO2 enters the Southern Ocean near 60 degrees S and is stored around 45 degrees S. This heat is transported to the ocean interior by the meridional overturning circulation (MOC) with wind changes playing an important role in the process. To isolate and quantify the latter effect, we apply an overriding technique to a climate model and decompose the total ocean response to CO2 increase into two major components: one due to wind changes and the other due to direct CO2 effect. We find that the poleward-intensified zonal surface winds tend to shift and strengthen the ocean Deacon cell and hence the residual MOC, leading to anomalous divergence of ocean meridional heat transport around 60 degrees S coupled to a surface heat flux increase. In contrast, at 45 degrees S we see anomalous convergence of ocean heat transport and heat loss at the surface. As a result, the wind-induced ocean heat storage (OHS) peaks at 46 degrees S at a rate of 0.07 ZJ yr(-1) (degrees lat)(-1) (1 ZJ = 10(21) J), contributing 20% to the total OHS maximum. The direct CO2 effect, on the other hand, very slightly alters the residual MOC but primarily warms the ocean. It induces a small but nonnegligible change in eddy heat transport and causes OHS to peak at 42 degrees S at a rate of 0.30 ZJ yr(-1) (degrees lat)(-1), accounting for 80% of the OHS maximum. We also find that the eddy-induced MOC weakens, primarily caused by a buoyancy flux change as a result of the direct CO2 effect, and does not compensate the intensified Deacon cell.