Forecast and simulation of stratospheric ozone filaments: A validation of a high-resolution potential vorticity advection model by airborne ozone lidar measurements in winter 1998/1999

In the framework of the Third European Stratospheric Experiment on Ozone pr oject Meridional Transport of Ozone in the Lower Stratosphere (METRO) an ai rborne ozone lidar has been flown on the French Falcon (Mystere 20) during winter 1998/1999 to investigate polar and subtropical filaments at midlatit udes. The objective of the METRO project is to quantify the proportion of t he transport of polar and subtropical air and their mixing into midlatitude air masses. The dynamical evolution of the northern winter hemisphere was simulated using a high-resolution advection model for potential vorticity ( PV): Modele Isentropique de transport Mesoechelle de l'Ozone Stratospheriqu e par Advection (MIMOSA). To validate the model for further studies, it was first utilized to forecast the appearance of filaments inside the range of the airplane so that each flight of the airborne campaign could be planned precisely. The vertical ozone distribution measured along the flight track s was then compared to the respective PV distribution simulated by the adve ction model. Correlation coefficients between 0.5 and 0.7 found over the al titude range where the filaments were observed show a good agreement betwee n PV and ozone filaments. An improvement of the correlation up to 0.8 by ho rizontal shifting of the ozone profiles against the PV evolution showed tha t small displacements of less than 1 degrees of the modeled PV filaments ca n occur. These displacements can be explained by the uncertainties of the i nput wind velocity data and of the lidar data. Thus we can conclude that th e PV advection model MIMOSA reproduces the position, size, and structure of polar filaments and subtropical intrusions well in. the range of the expec ted accuracy. The model is a suitable tool for further studies of the quant ification of the global, long-term transport and mixing of polar and subtro pical air into mid-latitudes.