Climate variability of the polar atmosphere based on historical radio sounding data

The results of the joint IARC/UAF and AARI project "Climate variability of the polar atmosphere revealed with historical radio soundings information" are presented. This project is an international effort to create with unified modern technique a new data set of the radio soundings, executed to the north of 650 N on the Russian coastal and island polar stations (data of more than million soundings), and to improve and extend data set of soundings from the drifting stations "North Pole" (more than 33,000 soundings). The data from 67 polar stations, 9 of which had begun observations in the middle 1930s, had been prepared. Together with existing archives, the new data set gives possibilities to investigate the seasonal and interannual variability, and trends of the main parameters of the troposphere, stratosphere, atmospheric boundary layer, and cloudiness.

Preliminary investigations of the free atmosphere above the Canadian Basin of the Arctic Ocean in winter fulfilled with data of the drifting stations "North Pole" showed that in 70% of the soundings the inversion base was on the surface; boundary layer height did not exceed 200 m; mean air temperature gradient in the inversion layer was 0.5-1.0 C0/100 m. Low-level jets were found in 30% of the soundings. During the investigated period (1955-1991) the boundary layer height and surface inversion depth tended to decrease, and the temperature change through the inversion tended to increase.

Long-term variations of the monthly mean air temperature and humidity in the free atmosphere above the North Polar Region (60-900 N) have been investigated using the original database, prepared by V. V. Maistrova's group. This database combines the results of soundings executed on 116 aerological stations, ship's observations and observations on the drifting stations "North Pole". The analysis of temperature trends for 1959-2000 shows that the mean air temperature in the North Polar Region increased in the low and middle troposphere (850-400 hPa) and decreased in the upper troposphere and in the stratosphere. At the same time, the total energy of the polar atmosphere attributed to the so-called "mean energetic level" does not show any identifiable trends, but undergoes long-term variation. Preliminary estimations of temporal variability of mean specific humidity on 850, 700, 500, 400 and 300 hPa levels showed pronounced increase from surface to 850 hPa and decrease above 850 hPa. The spatial distributions of air temperature and humidity trends demonstrate strong inhomogenity of relevant meteorological fields.