ANTARCTIC STRATOSPHERIC WINTER WARMING SINCE 1979

Polar climate has much larger changes than other areas over the globe, which is reflected not only near the surface but also in the stratosphere. Using the NCEP/NCAR, NCEP/DOE and ERA40 reanalysis, the decadal trends in temperatures and geopotential heights in the Southern　Hemisphere winter stratosphere were studied, and found that the Antarctic stratosphere has displayed statistically significant warming trends since the late 1970s. The warming mainly occurred in July-October with the maximum warming of about 7℃ at 30 hPa over the past 27 years (1979-2005) in the NCEP/NCAR and NCEP/DOE reanalysis, and in June-September, one month earlier than that in the NCEP/NCAR and NCEP/DOE data, with the maximum warming of more than 10℃ in the upper stratosphere (5 and 3 hPa) over the past 23-year (1979-2001) in the ERA40 data. The significant warming was centered over the polar cap in the upper stratosphere, however, it lay in the Australian side of the polar region in the middle and lower stratosphere. Geopotential heights in the Antarctic stratosphere also exhibited positive trends in response to temperature increasing. The maximum increase in geopotential heights was 450 meters at 10 hPa over the 27-year in the NCEP/NCAR and NCEP/DOE, but the increase was relatively smaller, about 300 meters over the 23 years in the ERA40. Further analysis shows that wave fluxes from the troposphere into the stratosphere also increased. It is the increasing in wave fluxes that leads to a stronger poleward residual meridional circulation in the stratosphere, thus a stronger subsidence in the polar region, which causes enhanced adiabatic heating in the polar region.