Stratospheric ozone intrusion over Zagreb, Croatia, on February 6, 1990

Abstract

On February 6, 1990 at 10.45 UTC the ozone volume fraction in Zagreb at RBI (182 m a.s.l.) suddenly rose from 2 ppb to 100 ppb and remained at unusually high values for another five hours. With a delay of approximately one hour at Puntijarka (which is 10 km north and 980 m a.s.l.) a rise from 40 ppb to out of scale (i.e. much higher than 100 ppb) occurred. Episodes of simultaneous high ozone values, however with decreasing intensity, have been observed at both stations again on February 7, and on February 8. Since insolation at this time of year in Zagreb is hardly sufficient for production of tropospheric ozone volume fractions higher than 30 ppb, a case of stratospheric intrusion is assumed. However, both stations are at relatively low altitude and at the higher one the ozone peak was registered later. Actual meteorological conditions over Europe and around Zagreb in particular were favourable for an ozone intrusion east of Zagreb earlier on February 6 in accordance with the observed behaviour. On these days a high pressure system rested over Europe. On February 6, surface wind in Zagreb blew from the east, thus explaining that the ozone package might have reached RBI prior to Punktijarka. The analysis of this event is given.

Keywords

• ozone
• volume fraction
• tropospheric
• high pressure system
• croatia
• ozon
• volumenanteil
• hochdruckgebiet
• zagreb
• kroatien