Stratosphere-troposphere exchange from the Lagrangian perspective: a case study and method sensitivities

[摘要] An important part of extra-tropical stratosphere-to-troposphere transportoccurs in association with baroclinic wave breaking and cut-off decay at thetropopause. In the last decade many studies have attempted to estimatestratosphere-troposphere exchange (STE) in such synoptic events with variousmethods, and more recently efforts have been made to inter-compare thesemethods. These inter-comparisons show large variations between estimates fromdifferent methods. This large uncertainty points to a need to thoroughlyevaluate such methods, assess the realism of the resulting STE estimates anddetermine the sensitivities to intrinsic parameters of the methods.The present study focuses on a trajectory-based Lagrangian method which hasbeen applied in the past to climatological studies. This method is appliedhere to the quantification of STE in the context of a typical baroclinic wavebreaking event. The analysis sheds light on (i) the complex three-dimensionaltemporal and spatial structures that are associated with the rapid inflow ofstratospheric air into the troposphere, (ii) the variation of STE mass fluxwith the choice of the dynamical tropopause definition within 1.5 to 5 PVU,(iii) the sensitivity of the results to resolution, and in particular theminimum spatial resolution of 1°×1°required to reasonably capture STE fluxes in this wave breaking event, (iv)the effective removal of spurious exchange events using a threshold residencetime larger than 8 h.

[学科分类] 大气科学