Stratosphere-troposphere exchange from the Lagrangian perspective: a case study and method sensitivities M. S. Bourqui McGill University, Montreal, Canada
Abstract. An important part of extra-tropical stratosphere-to-troposphere transport
occurs in association with baroclinic wave breaking and cut-off decay at the
tropopause. In the last decade many studies have attempted to estimate
stratosphere-troposphere exchange (STE) in such synoptic events with various
methods, and more recently efforts have been made to inter-compare these
methods. These inter-comparisons show large variations between estimates from
different methods. This large uncertainty points to a need to thoroughly
evaluate such methods, assess the realism of the resulting STE estimates and
determine the sensitivities to intrinsic parameters of the methods.
The present study focuses on a trajectory-based Lagrangian method which has
been applied in the past to climatological studies. This method is applied
here to the quantification of STE in the context of a typical baroclinic wave
breaking event. The analysis sheds light on (i) the complex three-dimensional
temporal and spatial structures that are associated with the rapid inflow of
stratospheric air into the troposphere, (ii) the variation of STE mass flux
with the choice of the dynamical tropopause definition within 1.5 to 5 PVU,
(iii) the sensitivity of the results to resolution, and in particular the
minimum 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 residence
time larger than 8 h.
Citation: Bourqui, M. S.: Stratosphere-troposphere exchange from the Lagrangian perspective: a case study and method sensitivities, Atmos. Chem. Phys., 6, 2651-2670, doi:10.5194/acp-6-2651-2006, 2006.