School of Earth Sciences - Research Publications
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ItemNo Preview AvailableAntarctic skin temperature warming related to enhanced downward longwave radiation associated with increased atmospheric advection of moisture and temperature(IOP PUBLISHING LTD, 2021-06)Abstract We investigate linear trends in Antarctic skin temperatures (temperatures from about the top millimeter of the surface) over the four seasons using ERA5 ensemble mean reanalysis data. During 1950–2020, statistically significant warming occurred over East and West Antarctica in spring, autumn and winter, and over the Antarctic Peninsula in autumn and winter. A surface energy budget analysis revealed that increases in downward longwave radiation related to increases in air temperature and total column integrated cloud had a key role in Antarctic surface warming. There were negative sea level pressure trends around the periphery of Antarctica throughout the year, and the associated circulation contributed to warm advection from the middle latitudes to West Antarctica and the Antarctic Peninsula. Over the interior of East Antarctica, increase in moisture advection from lower latitudes enhanced the low-level cloud cover. A two-dimensional parameter diagram showed that skin temperature trends for time segments longer than 30 years starting before 1960 exhibited statistically significant warming in autumn and winter in East and West Antarctica and the Antarctic Peninsula. In spring, West Antarctica also showed statistically significant warming for long segments. In summer, the Antarctic Peninsula had statistically significant warming trends for long segments and cooling trends for segments less than 30 years. For all the studied time intervals, when skin temperatures had statistically significant positive trends, increases in downward longwave radiation contributed more than 70% of the warming and vice versa. This result demonstrates that on all time and space scales, changes in downward longwave radiation associated with variations in air temperature and atmospheric moisture loading play a dominant role controlling skin temperatures.
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ItemA Climatology of the Marine Atmospheric Boundary Layer over the Southern Ocean from Four Field Campaigns during 2016–2018(American Geophysical Union, 2020-10-27)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.
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ItemAntarctic Peninsula warm winters influenced by Tasman Sea temperatures(NATURE RESEARCH, 2021-03-08)The Antarctic Peninsula of West Antarctica was one of the most rapidly warming regions on the Earth during the second half of the 20th century. Changes in the atmospheric circulation associated with remote tropical climate variabilities have been considered as leading drivers of the change in surface conditions in the region. However, the impacts of climate variabilities over the mid-latitudes of the Southern Hemisphere on this Antarctic warming have yet to be quantified. Here, through observation analysis and model experiments, we reveal that increases in winter sea surface temperature (SST) in the Tasman Sea modify Southern Ocean storm tracks. This, in turn, induces warming over the Antarctic Peninsula via planetary waves triggered in the Tasman Sea. We show that atmospheric response to SST warming over the Tasman Sea, even in the absence of anomalous tropical SST forcing, deepens the Amundsen Sea Low, leading to warm advection over the Antarctic Peninsula.