Towards understanding the impact of TTL cirrus clouds on troposphere-to-stratosphere transport

Although it is well accepted that air enters stratosphere through the tropical tropopause by large-scale upwelling, the detailed mechanisms of troposphere-to-stratosphere transport (TST) remain unclear. Recently, Corti et al. postulated that the radiative heating effect of cirrus clouds in the tropical tropopause layer (TTL) can be an important factor in affecting the rate of TST. Their results were confined to a one-dimensional view which may arguably apply to tropical-mean conditions. To examine the validity of this postulation in the real atmosphere, we use new observations of TTL cirrus acquired from Aura MLS and CALIPSO, along with trajectory analyses, to examine the impact of cirrus on TST when horizontal displacements of air parcels and spatial and temporal variations of cirrus distributions are taken into account. The trajectories of air parcels are sorted according to the cirrus cloud occurrence frequency and a set of cloud-influenced TST pathways are identified. Our preliminary analysis shows that the radiative heating associated with cirrus can contribute to a faster ascent of air from the troposphere to stratosphere, and that the spatial and temporal variations of cirrus impacts are significant.