Validation of a new operational package for the Lagrangian diagnosis of stratosphere-troposphere exchange at Environment Canada

A new operational diagnostic package for stratosphere-troposphere exchange (STE) has been developed for Environment Canada (EC). The STE calculations are made daily on the basis of 10-day global forecasts (0.3x0.3 degrees x 80 levels up to 0.1hPa x 1hour) produced by the EC GEM model. Following a Lagrangian approach, 18 million trajectories are calculated for 48h from five different times (0, 24, 48, 72, 96 hours) along each global forecast, starting from a global grid spanning the atmosphere from 600hPa to 10hPa. The trajectories crossing the 2PVU dynamical tropopause or the 380K isentrope are then selected and extended for four days forward or backward. A number of diagnostics are calculated, including global maps of the mass flux across the 2PVU tropopause and the 380K isentrope, and clusters of cross-tropopause transport events reaching the lower troposphere (700hPa). The resulting data set is global and will shed new insights into STE processes, their frequency of occurrence in different regions of the world, and their possible impacts on the chemical composition of the troposphere and the lower stratosphere, and on surface air quality. It will also be useful as a new reference for validating cross-tropopause fluxes in general circulation models or in chemistry transport models. This real-time forecasting of STE was used extensively in a recent observational campaign focussing on STE with balloon sondes launched daily from Montreal (QC, CA), Egbert and Walsingham (ON, CA) through the month of July 2010. This poster presents a validation of this diagnostic package against these balloon sonde measurements. Throughout the campaign, additional soundings were made whenever deep STT events (stratospheric air injected below 700hPa ) were forecasted. The results are very promising, with an excellent match between observations and forecasts.