An algorithm to detect tropopause folds from ozone soundings

Abstract

An algorithm has been developed to determine the occurrence of tropopause folds by an analysis of ozone soundings together with meteorological parameters, especially the potential vorticity. Tropopause folds transfer air and trace gases from the lower stratosphere into the troposphere. The algorithm detects folds by means of ozone anomalies in the troposphere, a simultaneous occurrence of low humidity and high values of potential vorticity. Furthermore the wind speed of the tropospheric wind profile has to exceed a jet stream velocity threshold of 30 m s-1. The application of the algorithm to the 2663 soundings taken at the sites Jülich, Uccle, Hohenpeißenberg and Payerne during six years (1989-1994) demonstrates that 46 tropopause folding events could be identified. The maximum of fold occurrence was found in March, and the minimum in April to June. The tropopause folded down to altitudes between 400 and 700 hPa during 75 % of the events.

Keywords

• tropopause folds
• ozone soundings
• vorticity
• tropopausenfaltungen
• ozonanomalien