A global climatology of stratosphere–troposphere exchange using the ERA-Interim data set from 1979 to 2011 ETH Zurich, IAC, Universitätstrasse 16, 8092 Zürich, Switzerland
27 Jan 2014
Received: 15 Mar 2013 – Published in Atmos. Chem. Phys. Discuss.: 02 May 2013 Abstract. In this study we use the ERA-Interim reanalysis data set from the
European Centre for Medium-Range Weather Forecasts (ECMWF) and
a refined version of a previously developed Lagrangian methodology to
compile a global 33 yr climatology of stratosphere–troposphere
exchange (STE) from 1979 to 2011. Fluxes of mass and ozone are
calculated across the tropopause, pressure surfaces in the
troposphere, and the top of the planetary boundary layer (PBL). This
climatology provides a state-of-the-art quantification of the
geographical distribution of STE and the preferred transport pathways,
as well as insight into the temporal evolution of STE during the last 33 yr.
Revised: 21 Sep 2013 – Accepted: 11 Dec 2013 – Published: 27 Jan 2014
We confirm the distinct zonal and seasonal asymmetry found in previous
studies using comparable methods. The subset of "deep STE", where
stratospheric air reaches the PBL within 4 days or vice versa, shows
especially strong geographical and seasonal variations. The global
hotspots for deep STE are found along the west coast of North America
and over the Tibetan Plateau, especially in boreal winter and
spring. An analysis of the time series reveals significant positive
trends of the net downward mass flux and of deep STE in both
directions, which are particularly large over North America.
The downward ozone flux across the tropopause is dominated by the
seasonal cycle of ozone concentrations at the tropopause and peaks in
summer, when the mass flux is nearly at its minimum. For the subset of
deep STE events, the situation is reversed and the downward ozone flux
into the PBL is dominated by the mass flux and peaks in early
spring. Thus surface ozone concentration along the west coast of North
America and around the Tibetan Plateau are likely to be influenced by
deep stratospheric intrusions.
We discuss the sensitivity of our results on the choice of the control
surface representing the tropopause, the horizontal and vertical resolution
of the trajectory starting grid, and the minimum residence time τ
used to filter out transient STE trajectories.
Citation: Škerlak, B., Sprenger, M., and Wernli, H.: A global climatology of stratosphere–troposphere exchange using the ERA-Interim data set from 1979 to 2011, Atmos. Chem. Phys., 14, 913-937, doi:10.5194/acp-14-913-2014, 2014.