scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

STP12 Abstracts
Berlin, 12 - 16 July 2010
SCOSTEP Symposium 2010
Wave mixing effects on minor chemical constituents in the MLT-region: Results from a
global CTM driven by high-resolution dynamics
Grygalashvyly Mykhaylo , Becker Erich , Sonnemann Gerd
Leibniz-Institute of Atmospheric Physics e.V. at the University Rostock
The dynamical fields a high-resolution mechanistic general circulation model (GCM) with
resolved gravity waves are used to drive a chemistry-transport model (CTM) of the
mesosphere/lower thermosphere (MLT). Both models have been used in previous studies.
Here, they are coupled in off-line mode in order to study the explicit effects of gravity waves
on the transport and photo-chemistry of minor constituents of the MLT. This is done on the
basis of sensitivity experiments. In our control simulation the CTM is driven with the full
dynamical fields from an annual cycle simulation with the GCM, where mid-frequency GWs
down to horizontal wave lengths of 350 km are resolved and their wave-mean flow interaction
is self-consistently induced by an advanced turbulence model. A perturbation simulation with
the CTM is defined by eliminating all mesoscale variations with horizontal wavelengths
shorter than 1000 km from the dynamical fields by means of spectral filtering before running
the CTM. This means, both CTM-simulations are driven by the same large-scale dynamics.
For reasons of consistency, we apply the same numerical grid and time step in both CTM
simulations.
The response of the CTM to gravity wave perturbations reveals strong effects on the trace-gas
concentrations. In particular, minor chemical constituents with large photochemical life-time
are strongly affected by vertical wave mixing, while constituents with short life-time reflect
the dependence of their reaction rates on meso-scale temperature perturbations and on the
changed distribution of long-living constituents. The mean model response varies with
latitude and season, but is strongest around the mesopause. We present detailed discussions of
the simulated gravity waves on the photo chemistry and highlight the consequences for our
understanding of the general circulation of the MLT.