Seasonal Antarctic pressure variability during the twentieth century from spatially complete reconstructions and CAM5 simulations
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As most permanent observations in Antarctica started in the 1950s, understanding Antarctic climate variations throughout the twentieth century remains a challenge. To address this issue, the non-summer multi-decadal variability in pressure reconstructions poleward of 60°S is evaluated and assessed in conjunction with climate model simulations throughout the twentieth and early twenty-first centuries to understand historical atmospheric circulation variability over Antarctica. Austral autumn and winter seasons show broadly similar patterns, with negative anomalies in the early twentieth century (1905–1934), positive pressure anomalies in the middle twentieth century (1950–1980), and negative pressure anomalies in the most recent period (1984–2013), consistent with concurrent trends in the SAM index. In autumn, the anomalies are significant in the context of estimates of interannual variability and reconstruction uncertainty across most of the Antarctic continent, and the reconstructed patterns agree best with model-generated patterns when the simulation includes the forced response to tropical sea surface temperatures and external radiative forcing. In winter and spring, the reconstructed anomalies are less significant and are consistent with internal atmospheric variability alone. The specific role of tropical SST variability on pressure trends in these seasons is difficult to assess due to low reconstruction skill in the region of strongest tropical teleconnections, the large internal atmospheric variability, and uncertainty in the SST patterns themselves. Indirect estimates of pressure variability, whether through sea ice reconstructions, proxy records, or improved models and data assimilation schemes, will help to further constrain the magnitude of internal variability relative to the forced responses expected from SST trends and external radiative forcing.
Data from both the station-based and spatial pressure reconstructions are available from figshare at the following URLs: https://doi.org/10.6084/m9.figshare.3412813 (station reconstructions) and https://doi.org/10.6084/m9.figshare.5325541 (spatial reconstructions). Data for the climate model simulations may be downloaded by following the links at http://www.cesm.ucar.edu/experiments/cesm1.1/LE, or by contacting the authors. RLF, CAG, LNC and MJG acknowledge support from the National Science Foundation (NSF), Grant PLR-1341621, while DPS acknowledges support from NSF Grant PLR-1341527. The Climate Variability and Change Working Group of the Community Earth System Model led the production of the CAM5 experiments with time-varying tropical or global SSTs and time-varying radiative forcing. This material is based upon work supported by the National Center for Atmospheric Research, which is a major facility sponsored by the National Science Foundation under Cooperative Agreement no. 1852977.
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