Variability and trends in Antarctic surface temperatures from in situ and satellite infrared measurements

The surface air temperatures observed from stations in Antarctica have been shown to have predominantly positive trends that are as high as 0.5 degree s C decade(-1) along the Antarctic Peninsula. To evaluate whether the trend s are caused by a local or large-scale phenomenon in the Antarctic region, surface temperatures inferred from infrared satellite data from 1979 to 199 8 have been analyzed in combination with data from 21 stations that have lo ng record lengths. The surface temperatures derived from infrared data are coherent spatially and temporally and are shown to agree well with Antarcti c station data with a correlation coefficient of 0.98 and a standard deviat ion of about 3 degrees C. The trend analysis on station data yielded on the average 0.012 +/- 0.008 degrees C yr(-1) and -0.008 +/- 0.025 degrees C yr (-1) for the 45- and 20-yr record, respectively. The latter reasonably agre es with the trend of -0.042 +/- 0.067 degrees C yr(-1) inferred from the sa tellite 20-yr record. The 20-yr record length is shown to be about the mini mum length required for a meaningful trend analysis study. However, interan nual fluctuations of the temperatures are large and the 95% confidence leve l for the satellite trends ranges from -0.177 to 0.094 degrees C yr(-1) for the Antarctic ice sheet. Nevertheless, the observed cooling is intriguing, especially since it is compatible with the observed trend in the sea ice c over. In the sea ice regions, the northernmost positions of the ice edge ar e shown to be influenced by alternating warm and cold anomalies around the Continent. The pattern of these anomalies is consistent with that of the An tarctic circumpolar wave but with predominantly mode-3 instead of mode-2 wa ve as reported previously.