Is the dramatic surface warming observed in the Antarctic Peninsula also present throughout the troposphere?

The ~2.5°C surface warming in the central western Antarctic Peninsula observed over the last 50-years is the largest seen in the Southern Hemisphere. However, there is not a single series of local upper-air observations contemporaneous with the warming with which to ascertain what temperature changes have occurred above the surface. In order to answer this question, and therefore to help to determine the physical processes behind the warming, two quality-controlled daily upper-air temperature datasets - from Faraday (1956-82) and Bellingshausen (1973-99) stations - are combined to produce a 44-year record of monthly mean temperature at Faraday at four different tropospheric heights from 1956 to 1999. Unfortunately, due to a significant amount of early Bellingshausen data being missing, there is very little overlap between these two time series: therefore NCEP/NCAR reanalysis data, interpolated to the station positions, are utilised to determine the mean monthly temperature difference between the two stations. A comparison, using more than 40 months when there were sufficient daily observations for a monthly value to be produced for both stations, demonstrates that the station temperature differences derived from the reanalysis are extremely close to those in the observations; this indicates that the methodology employed to extend the Faraday time series is appropriate. For those months when data from neither station are available, further limited observational data from Marambio station are utilised where possible, together with the reanalysis data at Faraday with the mean monthly bias, as determined by a comparison to all available observations of that month, removed.

Initial findings reveal that there has indeed been an increase in temperature at upper-levels, although its magnitude is less than that at the surface and the seasonal variation in the warming is very different at upper levels. In winter - the season of greatest surface warming, believed to be linked to a reduction in sea ice in the Bellingshausen Sea to the west of the Peninsula - the upper-level warming is significantly reduced in comparison. However, the warming in summer is actually greater than in winter and also greater than that at the surface. This suggests that the Peninsula warming reflects changes in the regional atmospheric circulation in addition to local surface processes.