Global large-scale stratosphere-troposphere exchange in modern
Alexander C. Boothe and Cameron R. Homeyer
School of Meteorology, University of Oklahoma, Norman, Oklahoma, USA
Received: 30 Aug 2016 – Accepted for review: 19 Oct 2016 – Discussion started: 26 Oct 2016
Abstract. Stratosphere-troposphere exchange (STE) has important and significant impacts on the chemical and radiative properties of the upper troposphere and lower stratosphere. This study presents a 15-year climatology of global large-scale STE from four modern reanalyses: ERA-Interim, JRA-55, MERRA-2, and MERRA-1. STE is separated into four categories for analysis to identify the significance of known transport mechanisms: 1) vertical stratosphere-to-troposphere transport (STT), 2) vertical troposphere-to-stratosphere transport (TST), 3) lateral STT (that occurring between the tropics and the extratropics and across the tropopause "break"), and 4) lateral TST.
In addition, this study employs a method to identify STE as that which crosses the lapse-rate tropopause (LRT), while most previous studies have used a potential vorticity (PV) isosurface as the troposphere-stratosphere boundary. PV-based and LRT based STE climatologies are compared using the same reanalysis output (ERA-Interim). The comparison reveals quantitative and qualitative differences, particularly in the geographic representation of TST in the polar regions.
Based upon spatiotemporal integrations, we find STE to be STT-dominant in ERA-Interim and JRA-55 and TST-dominant in the MERRA reanalyses. Time series during the 15-year analysis period show long-term changes that are argued to correspond with changes in the Brewer-Dobson circulation.
Boothe, A. C. and Homeyer, C. R.: Global large-scale stratosphere-troposphere exchange in modern
reanalyses, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-788, in review, 2016.