Simulation of the Seasonal Variation of Mesospheric Zonal Wind Reversal
with Anisotropic Gravity Waves
Abstract
The observed seasonal variation of zonal wind reversal in the mesosphere
and lower thermosphere (MLT) is often not well captured in whole
atmosphere general circulation models (GCMs) with current gravity wave
parameterization schemes. In this study, we investigate the possible
physical mechanisms controlling this seasonal variation. It is found
that adaptation of an anisotropic parameterized gravity wave source
spectrum with stronger eastward and weaker westward propagating waves
can reproduce this seasonal feature. Furthermore, additional
stratospheric forcing is needed to control the large winter
stratospheric zonal wind and alleviate the “cold-pole” problem in the
southern winter. This is accomplished by the application of an inertial
gravity wave parameterization scheme. With these changes, the Whole
Atmosphere Community Climate Model with thermosphere and ionosphere
extension (WACCM-X) can produce zonal mean zonal wind that is in better
agreement with climatology from the stratosphere to MLT, including the
seasonal variation of the zonal wind reversal.