Ozone, Temperature, and Wind Field Measurements in a Tropopause Fold: Comparison with a Mesoscale Model Simulation

Abstract

In March 1995 a tropopause fold was observed at the Observatoire de Haute Provence (44°N, 6°E) using simultaneous high-resolution measurements of ozone, temperature, and wind. This unique dataset was provided by an ozone lidar, a temperature lidar, and a wind field radar. These data are described and related to the meteorological context. Comparisons with mesoscale modeling of this episode are conducted to answer the question of whether there is any spatial or temporal shift between the model outputs and the observations. Temperature comparison shows a very good agreement between the modeled and the measured static stability, discarding the hypothesis of any vertical shift. Comparison of the measured and modeled meridional components of the wind insures that the model reproduces the horizontal structure of the front and its temporal evolution. To check further the model?s ability to reproduce mesoscale structures of the flow, the relationship between ozone and potential vorticity is investigated. First, a significant association is found between potential vorticity and ozone. Their distributions are in phase and the fold can be equally defined using ozone or potential vorticity. However, second-order differences are found in the vicinity of the jet streak where turbulent mixing entrains tropospheric air within the lowermost stratosphere. Second, ozone and potential vorticity ratios, which are calculated for the different air masses in the front, compare well with climatological ratio values. This is in good agreement with the well-known view of tropopause folding as an isentropic deformation of a zone of strong ozone and potential vorticity gradients. Third, this dataset is used to model the relationship between ozone and potential vorticity, which gives an easy way to switch from one field to the other.