Long-term variability of the free atmosphere in the Arctic

The long-term variability of the free atmosphere temperature in the North Polar Region (60-900 N) was investigated with database, containing the results of observations of 116 meteorological stations, ship's observations and observations on the drifting stations "North Pole". The special procedure was developed for accounting data from moving platforms (ships, drifting stations) in the monthly averaged data set. The analysis of trends was made for the all period, covered by data (1959-1998) as well as for periods 1959-1979 and 1979-1998. In mean the air temperature in the North Polar Region increased in the main part of troposphere (850-400 mb) and decreased in the upper troposphere and in the stratosphere. The absolute minimum of stratosphere temperature and maximum of troposphere temperature were found in 1998.

The interannual variability of air temperature in the lower troposphere shows only negative anomalies during 1959-1980. The maximal temperature anomaly was found in 1978 and 1979 (-1.7s). In opposite only positive anomalies of air temperature of the whole troposphere were detected after 1980. Its value exceeds 3s in 1998. In stratosphere till 1978 the positive anomalies of air temperature dominate. Then the anomalies were mainly negative and the quantity of large anomalies, up to -3s, increased, especially in spring and summer. The trends of the air temperature gradient were positive in the whole atmosphere indicating the increase of vertical instability of the polar atmosphere.

The analysis of trends spatial distribution showed that in the low troposphere (850 mb), despite mean warming, there were regions with weak negative trends. In winter it is the northern part of Siberia and Canadian Archipelago, in summer - the northern part of Europe. In winter tropopause (250 mb) the positive trends dominated in the central part of the Arctic Basin. In stratosphere the strongest cooling existed during all seasons above the Greenland, Barents and Kara seas and adjust regions of Europe. The sliding trends were calculated for investigation of the interannual variations of heating or cooling rates on different heights.