Articles | Volume 35, issue 4
Regular paper
13 Jul 2017
Regular paper |  | 13 Jul 2017

On the influence of zonal gravity wave distributions on the Southern Hemisphere winter circulation

Friederike Lilienthal, Christoph Jacobi, Torsten Schmidt, Alejandro de la Torre, and Peter Alexander

Abstract. A mechanistic global circulation model is used to simulate the Southern Hemisphere stratospheric, mesospheric, and lower thermospheric circulation during austral winter. The model includes a gravity wave (GW) parameterization that is initiated by prescribed 2-D fields of GW parameters in the troposphere. These are based on observations of GW potential energy calculated using GPS radio occultations and show enhanced GW activity east of the Andes and around the Antarctic. In order to detect the influence of an observation-based and thus realistic 2-D GW distribution on the middle atmosphere circulation, we perform model experiments with zonal mean and 2-D GW initialization, and additionally with and without forcing of stationary planetary waves (SPWs) at the lower boundary of the model. As a result, we find additional forcing of SPWs in the stratosphere, a weaker zonal wind jet in the mesosphere, cooling of the mesosphere and warming near the mesopause above the jet. SPW wavenumber 1 (SPW1) amplitudes are generally increased by about 10 % when GWs are introduced being longitudinally dependent. However, at the upper part of the zonal wind jet, SPW1 in zonal wind and GW acceleration are out of phase, which reduces the amplitudes there.

Short summary
Gravity waves (GWs) are one of the most important dynamical features of the middle atmosphere that extends from the tropopause to the lower thermosphere. They originate from the troposphere and propagate upward. Here, we show the impact of the horizontal GW distribution in the lower atmosphere on the dynamics of the middle atmosphere using a global circulation model. As a result, we find that non-zonal GW structures can force additional stationary planetary waves.