Pathways and timescales for troposphere-to-stratosphere transport via the tropical tropopause layer and their relevance for very short lived substances

摘要

We have carried out studies of the transport between the tropical boundary layer, the tropical tropopause layer, and the stratosphere during January 2001 using both atmospheric tracers in a transport model and air parcel trajectories. Most of the transport (approximately two thirds) from the planetary boundary layer (BL) into the tropical tropopause layer (TTL) occurs vertically above the Indian Ocean and the Indonesian and west Pacific regions, consistent with transport dominated by convection. Transport from the base of the TTL into the stratosphere above the dynamical tropopause is dominated (approximately 95%) by transport into the extratropical lowermost stratosphere (ELS) with a much smaller fraction entering the stratospheric “overworld.” Overall, transport from the BL to the ELS is sufficiently rapid that this represents an important route by which very short lived substances (VSLS), emitted at the surface, can influence lower stratospheric ozone. The two approaches, using high-resolution trajectories and a lower-resolution transport model, yield generally similar results, increasing confidence that chemistry transport models can capture transport sufficiently well for chemical assessment modeling of the role of VSLS.