Cold air outbreaks and their signature in the ozonometric data at the mountain station near Kislovodsk, Russia

Abstract

International audienceTwo cases of cold air outbreak in November 2001 are analyzed on the basis of ozone concentration measurements and weather data at the mountain station (43°44' N, 42°43 E, 2070 m a.s.l.) near Kislovodsk, North Caucasus, Russia. Two cold fronts, with fast clearing up in the rear of the cloud zone, passed the station in the morning of 12 and 16 November. In both cases, the ozone concentration drops down to 7?8 ppb within the frontal cloud zones, under 100% relative humidity, RH, and then sharply increases to 43?45 ppb in dry (RH about 50%), cold air during several hours. After a warm front passage (12 November) or RH growth in the cold post-frontal airmass (16 November), the ozone concentration decreases again to its average values near 30 ppb. Neither diurnal cycle nor photochemical generation could produce in the ozonometric data this specific "drop-and-peak'' signature which is considered to be caused by cold outbreak with post-frontal flow of "dry air stream'' type. Synoptic situation and tropopause topography are analyzed using the objective analysis data and METEOSAT images in the water vapor radiation band. It is concluded that the ozone growth in the rear of the cold fronts is associated with sinking of substratospheric or stratospherically influenced air from the areas of tropopause folding. Motion of cold surges with their frontal zones, jet streams, and tropopause folds is analyzed, including development of wave disturbances at the streamers and formation of substratospheric air "tongues'' underflowing the high tropopause and representing "aged'' intrusions