Stratospheric Transport

Abstract

Improvements in our understanding of transport processes in the stratosphere have progressed hand in hand with advances in understanding of stratospheric dynamics and with accumulating remote and in situ observations of the distributions of, and relationships between, stratospheric tracers. It is convenient to regard the stratosphere as being separated into four regions: the summer hemisphere, the tropics, the wintertime midlatitude ''surf zone'', and the winter polar vortex. Stratospheric transport is dominated by mean diabatic advection (upwelling in the tropics, downwelling in the surf zone and the vortex) and, especially, by rapid isentropic stirring within the surf zone. These characteristics determine the global-scale distributions of tracers, and their mutual relationships. Despite our much-improved understanding of these processes, many chemical transport models still appear to exhibit significant shortcomings in simulating stratospheric transport, as is evidenced by their tendency to underestimate the age of stratospheric air.

Earth System Chemistry integrated Modelling (ESCiMo) with the Modular Earth Submodel System (MESSy) version 2.51

“…We use the dust emission scheme of Tegen et al (see Figs. E58 and E59 for input parameters;2002), which was implemented in the submodel ONEMIS by Gläser et al (2012). The wind stress threshold for dust emissions is corrected by a factor of 0.86 in accordance with Tegen et al (2004).…”

“…It refers to the large-scale residual circulation (RC) with upwelling in the tropics and sinking motion at mid-and high latitudes in the stratosphere and winter mesosphere. Moreover, quasihorizontal mixing processes contribute to the stratospheric transport (Plumb, 2002). The RC is often expressed in terms of the tropical upward mass flux (F trop ), which corresponds to the upward-directed mass transport in the tropics and is balanced by the downward mass fluxes in the extratropics of both hemispheres (Holton, 1990).…”

Anthropogenic radionuclides in atmospheric air over Switzerland during the last few decades

“…Our results show that significant fractions of radioactive aerosols (possibly small particles o0.1 mm) remain in the stratosphere for timescales of the order of several decades. Mean residence time of stratospheric air can be obtained from observations of tracer changes in the atmosphere [35][36][37][38][39][40][41] . We used an exponential distribution model (box model) to interpret the trend of Pu and 137 Cs in the stratosphere of Switzerland.…”

The COST 723 Action

“…Another barrier divides the extratropics from the tropics, forming a 'tropical pipe' in the mid-stratosphere (Plumb, 2002). This barrier is separated from the one mentioned above (associated with the subtropical jets) by a region extending from θ = 370 K to about θ = 450 K, centred at θ = 400 K, and in which meridional exchange is favoured (Waugh, 1996).…”