Intrusion of stratospheric ozone to the free troposphere through tropopause folds - A case study

Simultaneous ozone radiosoundings at Jaegersborg north of Copenhagen, Denma rk, and at Gardermoen north of Oslo, Norway, at 12 UTC on 21 March, 1994, b oth show a pronounced peak of ozone in the free troposphere. A study involv ing routine radiosoundings as well as analysed numerical weather prediction (NWP) model data shows that a tropopause folding occurred over the Davis S trait and the southern part of Greenland about two days before the radiosou ndings. Trajectory calculations performed using the same NWP model data ind icate that air parcels corresponding to the observed ozone peaks at Jaegers borg and at Gardermoen have passed trough the tropopause fold thus bringing down ozone rich air from the stratospheric ozone layer to the free troposp here. A quantitative simulation of this transport phenomenon is performed u sing an atmospheric three-dimensional long-range dispersion model. By fitti ng the simulated vertical profiles of ozone concentration to the observed p rofiles, an estimate is obtained of the rate of ozone intrusion through the tropopause fold. (C) 2000 Elsevier Science Ltd. All rights reserved.