Stratosphere–troposphere exchange (STE) has important impacts on thechemical and radiative properties of the upper troposphere and lowerstratosphere. This study presents a 15-year climatology of global large-scaleSTE from four modern reanalyses: ERA-Interim, JRA-55, MERRA-2, and MERRA. STEis separated into three regions (tropics, subtropics, and extratropics) andtwo transport directions (stratosphere-to-troposphere transport or STT andtroposphere-to-stratosphere transport or TST) in an attempt to identify thesignificance of known transport mechanisms. The extratropics and tropics areseparated by the tropopause . Any STE occurring between the tropicsand the extratropics through the tropopause break is considered subtropicalexchange (i.e., in the vicinity of the subtropical jet).In addition, this study employs a method to identify STE as that whichcrosses the lapse-rate tropopause (LRT), while most previous studies haveused a potential vorticity (PV) isosurface as the troposphere–stratosphereboundary. PV-based and LRT-based STE climatologies are compared using theERA-Interim reanalysis output. The comparison reveals quantitative andqualitative differences, particularly for TST in the polar regions.Based upon spatiotemporal integrations, we find STE to be STT dominant inERA-Interim and JRA-55 and TST dominant in MERRA and MERRA-2. The sources ofthe differences are mainly attributed to inconsistencies in therepresentation of STE in the subtropics and extratropics. Time series duringthe 15-year analysis period show long-term changes that are argued tocorrespond with changes in the Brewer–Dobson circulation.
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