Effects of Gravity Waves in the SKYHI General Circulation Model

Parameterization of gravity wave effects in global circulation models is a problem of significant importance for both climate and weather forecasting applications. The focus of attention in studies of gravity wave effects has largely been near the tropopause or in the mesosphere. Gravity wave effects in the stratosphere are receiving only comparitively recent attention for their role in driving the tropical quasi-biennial oscillation and the zonal-mean residual circulation in the stratosphere. We have included parameterization of gravity wave effects [Alexander and Dunkerton, 1999] in the SKYHI general circulation model in order to study their role in shaping the wind and temperature structure and trace constituent transport patterns in the model stratosphere. SKYHI is a self-consistent comprehensive general circulation model of the troposphere, stratosphere, and mesosphere. In this study, gravity wave mean-flow forcing effects have been parameterized in SKYHI model runs using 3.6 x 3 degree horizontal resolution and 40 vertical levels between the surface and 80 km. The parameterized gravity waves are also allowed to interact with the wavenumber 1-2 planetary-scale waves in the model. The focus of this study is on the relative importance of parameterized gravity wave dissipation and resolved planetary wave dissipation in driving stratospheric circulation patterns. Although the magnitude of gravity wave mean-flow forcing in the stratosphere is small compared to planetary-wave forcing, the gravity waves play an important intermediary role by altering the pattern of planetary wave propagation and dissipation in winter. Gravity wave forcing also significantly alters the timing of the transition to westward stratospheric winds in the spring-to-summer season.