Stratosphere‐troposphere exchange: A review, and what we have learned from STACCATO

Abstract

[1] This paper provides a review of stratosphere-troposphere exchange (STE), with a focus on processes in the extratropics. It also addresses the relevance of STE for tropospheric chemistry, particularly its influence on the oxidative capacity of the troposphere. After summarizing the current state of knowledge, the objectives of the project Influence of Stratosphere-Troposphere Exchange in a Changing Climate on Atmospheric Transport and Oxidation Capacity (STACCATO), recently funded by the European Union, are outlined. Several papers in this Journal of Geophysical ResearchAtmospheres special section present the results of this project, of which this paper gives an overview. STACCATO developed a new concept of STE in the extratropics, explored the capacities of different types of methods and models to diagnose STE, and identified their various strengths and shortcomings. Extensive measurements were made in central Europe, including the first monitoring over an extended period of time of beryllium-10 ( 10 Be), to provide a suitable database for case studies of stratospheric intrusions and for model validation. Photochemical models were used to examine the impact of STE on tropospheric ozone and the oxidizing capacity of the troposphere. Studies of the present interannual variability of STE and projections into the future were made using reanalysis data and climate models.

Aerosol and trace‐gas measurements in the Darwin area during the wet season

“…The Tropical Tropopause Layer (TTL) is the subject of much ongoing study to reduce uncertainty in climate change predictions and the nature of stratosphere-troposphere exchange [Stohl et al, 2003] and consequent impacts on stratospheric ozone [Esler et al, 2001]. Furthermore, aerosol particles lifted from the surface have indirect effects influencing precipitation and radiation fluxes [Lohmann and Feichter, 2005;McFiggans et al, 2006].…”

Resolution Dependency of Numerically Simulated Stratosphere-to-Troposphere Transport Associated with Mid-Latitude Closed Cyclones in Early Spring around Japan

“…The STT usually occurs with a cross-tropopause flow, induced by the tropopause folding caused by the developed mid-latitude cyclones, accompanied by dry airstream from upper to lower levels (e.g., Johnson and Viezee 1981;Cooper et al 2001). However, many other processes (e.g., breaking gravity waves, mesoscale convective systems) are related to the STT (e.g., Stohl et al 2003). Tropopause folding is often formed during the development of a cut-off low (e.g., Stohl et al 2003), which is a subset of the mid-latitude cyclones.…”

“…However, many other processes (e.g., breaking gravity waves, mesoscale convective systems) are related to the STT (e.g., Stohl et al 2003). Tropopause folding is often formed during the development of a cut-off low (e.g., Stohl et al 2003), which is a subset of the mid-latitude cyclones.…”

“…This sometimes includes an irreversible exchange from the stratosphere to the troposphere, with the transport of potentially ozone-rich air into the PBL (e.g., Stohl et al 2003).…”

Vorticity, deformation and divergence signals associated with stratosphere–troposphere exchange

“…Most of these processes are linked to distinct flow phenomena (tropopause folds, extratropical cyclones, PV streamers, cut-offs) and hence distinct signatures of the velocity field. A concise review of the many processes leading to STE is given in Stohl et al (2003) or in Sprenger et al (2009). The latter study investigates deep STE and the involved diabatic process: clear-air turbulence (CAT) turns out to be mostly only important for stratosphereto-troposphere transport (STT), latent heat release only for troposphere-to-stratosphere transport (TST), whereas radiative processes are linked to both STT and TST.…”