Changes in Antarctic Peninsula tropospheric temperatures from 1956 to 1999: a synthesis of observations and reanalysis data

The surface warming at Faraday station in the western Antarctic Peninsula is one of the largest observed anywhere over the last 50 years, yet the physical mechanisms driving this climate change are poorly understood. In this paper we synthesize radiosonde temperature observations from three Peninsula stations and NCEP-NCAR reanalysis data in order to examine contemporaneous regional tropospheric temperature trends (1956-99), which may in turn help us to understand better the causes of the surface warming. The reanalysis data are utilized in two ways: (i) to provide long-term mean monthly offsets between Faraday, which ceased radiosonde observations in 1982, and two other stations in the region having more recent data, Bellingshausen and Marambio, in order to create post-1982 simulated Faraday data; (ii) after having any spurious trends and bias removed, to provide directly a monthly value for Faraday when no equivalent value from regional observations is available. Using available months of overlap, a comparison between temperature observations and simulated data suggests that the latter are a reasonable facsimile of the former. The synthesized time-series of tropospheric temperatures reveal a statistically significant mean annual tropospheric (850-300 hPa) warming above Faraday between 1956 and 1999 of similar to0.027 +/- 0.022degreesC year(-1). Winter and summer both show a warming trend, with significance varying with height and season. Annually, the mean tropospheric warming is half that at the surface, Unlike the surface warming, the calculated tropospheric warming trend is no greater than observed at other Antarctic stations, and indeed is not significantly greater than the background global warming trend for most of the period examined. Thus, we cannot dismiss the possibility that the Peninsula surface warming may simply be a response to a global warming magnified by the observed strong regional feedback between sea-ice extent and surface temperature during winter.

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