ON THE LOW OZONE VALUES OVER SCANDINAVIA DURING THE WINTER OF 1991-1992

During the winter of 1991-1999, ozone values over Scandinavia and northern Europe were exceptionally low. The sea surface temperatures in the southern part of the North Atlantic were 0.5-1.0 degrees C higher than the normal, whereas the corresponding temperatures in the Greenland waters were about normal or a little lower than normal. The normal is based on observations during the period 1957-1980 (WMO, 1992). The increased temperature gradient in the sea surface resulted in an increase in the air temperature gradient. As a consequence, strong southwesterly winds with frequent low pressure activity dominated in the North Atlantic during the winter of 1991-1992. In the southwest wind-flow, ascending motion in the troposphere and the lower stratosphere was persistent, especially during the month of January 1992, The ascending motion lifted the tropopause and the lower stratosphere to higher levels and attempted to establish a secondary tropopause due to tropopause folding. The ozone partial pressure between the original tropopause and the secondary was then strongly reduced,