Antarctic near-surface air temperatures compared with ERA-Interim values since 1979

Abstract

ERA-Interim reanalysis for near-surface air temperature agrees well with land stations in most regions with the principal exception of the Antarctic. Here we compare annual and monthly values from 40 manned and automatic weather stations (AWSs) with ERA-Interim between 1979 and 2013. In terms of absolute differences between ERA-Interim and the station observations, ERA-Interim is biased warm (by up to 5 °C) at the few inland stations, but biased cool at lower latitudes between 65°S and 78°S (by up to 6 °C) at some locations. These biases tend to reduce between the period 1979–1990 and 2002–2013 at many sites, but they increase at three sites on the Antarctic Peninsula. Comparisons of differences in variability show one or nine stations have standard deviation values for ERA-Interim 20% less or more than the station series. Time series agreement in terms of monthly correlations of anomalies is good (r ≥ 0.89) for most of the stations, but seven are below 0.80, with ten between the two thresholds. Finally, we produce an ‘Antarctic’ average time series by simple averaging of the 40 stations and ERA-Interim time series, as well as calculating an average based on all land points across the Antarctic from ERA-Interim. The series based on all land points is more variable on the year-to-year timescale and trends for the overall period are reduced.