caa a22 4500 528787292 20181224030230.0 cr unu---uuuuu 180924s2010 xx s 000 0 eng 10.3929/ethz-b-000022284 doi 10.5194/acp-10-7929-2010 doi (ETHRESEARCH)oai:www.research-collection.ethz.ch:20.500.11850/22284 Transport timescales and tracer properties in the extratropical UTLS [Elektronische Daten] [Peter Hoor, Heini; id_orcid 0000-0001-9674-4837 Wernli, Michaela I. Hegglin, Harald Bönisch] Atmos. chem. phys. Open access ethresearch A comprehensive evaluation of seasonal backward trajectories initialized in the northern hemisphere lowermost stratosphere (LMS) has been performed to investigate the factors that determine the temporal and spatial structure of troposphere-to-stratosphere-transport (TST) and it's impact on the LMS. In particular we explain the fundamental role of the transit time since last TST (tTST) for the chemical composition of the LMS. According to our results the structure of the LMS can be characterized by a layer with tTST<40 days forming a narrow band around the local tropopause. This layer extends about 30 K above the local dynamical tropopause, corresponding to the extratropical tropopause transition layer (ExTL) as identified by CO. The LMS beyond this layer shows a relatively well defined separation as marked by an aprupt transition to longer tTST indicating less frequent mixing and a smaller fraction of tropospheric air. Thus the LMS constitutes a region of two well defined regimes of tropospheric influence. These can be characterized mainly by different transport times from the troposphere and different fractions of tropospheric air. Carbon monoxide (CO) mirrors this structure of tTST due to it's finite lifetime on the order of three months. Water vapour isopleths, on the other hand, do not uniquely indicate TST and are independent of tTST, but are determined by the Lagrangian Cold Point (LCP) of air parcels. Most of the backward trajectories from the LMS experienced their LCP in the tropics and sub-tropics, and TST often occurs 20 days after trajectories have encountered their LCP. Therefore, ExTL properties deduced from CO and H2O provide totally different informations on transport and particular TST for the LMS. Creative Commons Attribution 3.0 Unported http://creativecommons.org/licenses/by/3.0 ethresearch Hoor Peter joint author Wernli Heini; id_orcid 0000-0001-9674-4837 joint author Hegglin Michaela I. joint author Bönisch Harald joint author Atmospheric Chemistry and Physics Munich : European Geophysical Society 10 (16), pp. 7929-7944 1680-7375 http://hdl.handle.net/20.500.11850/22284 text/html WWW-Backlink auf das Repository (Open access) 1 Journal Article ethresearch ETHRESEARCH 856 40 http://hdl.handle.net/20.500.11850/22284 text/html WWW-Backlink auf das Repository (Open access) ETHRESEARCH 700 1- Hoor Peter joint author ETHRESEARCH 700 1- Wernli Heini; id_orcid 0000-0001-9674-4837 joint author ETHRESEARCH 700 1- Hegglin Michaela I. joint author ETHRESEARCH 700 1- Bönisch Harald joint author ETHRESEARCH 773 0- Atmospheric Chemistry and Physics Munich : European Geophysical Society 10 (16), pp. 7929-7944 1680-7375 BK010053 XK010053 XK010000 ETHRESEARCH ETHRESEARCH ETHRESEARCH Journal Article Open access