| A new tool for the Lagrangian diagnosis of stratosphere-troposphere exchange (STE) was developed for Environment Canada and became operational in July 2010, providing unique, high-resolution daily forecasts of STE over the globe. This thesis offers a comprehensive validation of these STE forecasts in the context of an ozonesonde balloon campaign conducted at three locations in Eastern Canada from 12 July to 4 August 2010. The STE forecasts are calculated using a Lagrangian kinematic trajectory methodology based on the high-resolution global GEM model forecasts at Environment Canada. Both observations and the STE forecasts during this period showed much larger frequency of stratospheric air intrusions deep into the troposphere at all locations compared to past studies. The STE dataset compares reasonably well with the observations above 500 hPa, yet is found to underestimate the frequency of events reaching below 700 hPa level. Sources of error can possibly be introduced by (1) errors in the 6-day global GEM forecasts, (2) errors in the identification of air with stratospheric origin in observations, and/or (3) the lack of convective and turbulent mixing representation in the trajectory model. Despite these large sources of errors, the STE forecasts turn out to be one of the best datasets available for the STE studies, being useful to estimate the currently controversial STE contribution to the tropospheric ozone budget in the free troposphere as well as in the boundary layer. |
