Lagrangian spectral parameterization of gravity wave drag induced by cumulus convection in the Goddard Earth Observing System (GEOS5) GCM

Momentum transport by unresolved gravity waves is one of the crucial factors for the reasonable numerical simulations of the global circulations of the middle atmosphere. For this reason, gravity wave drag (GWD) parameterization has been regarded as a standard component in most of present-day middle atmosphere general circulation models (GCMs). However, current GWD parameterizations are all based on the column dynamics. That is, gravity-wave packets launched at a certain level always propagate to the model's top boundary within one GCM time step. Given that gravity waves in general propagate at a finite propagation speed in the horizontal and vertical directions, realism of column-based GWD parameterizations may be limited. Therefore, for more reliable parameterization, wave propagation characteristics need to be explicitly considered. Recently, an effort has been made to explicitly include gravity-wave propagation in GWD parameterization (Song and Chun 2006), and as a result of this effort, a Lagrangian spectral parameterization of GWD induced by cumulus convection has been developed based on the ray theory, and it has been tested in the NCAR Whole Atmosphere Community Climate Model. In this study, we implement this Lagrangian GWD parameterization into the Goddard Earth Observing System (GEOS) GCM version 5, and examine its impact in the seasonal simulations of the GEOS5. The effects of the Lagrangian parameterization are examined in the GEOS5 GCM with variable horizontal resolutions. Through several experiments conducted at various horizontal resolutions, we examine effects of the spatial variation of background variables on the propagation characteristics of gravity waves, and we discuss impacts of the horizontal refraction of gravity waves in wave momentum forcing.

Reference

Song, I.-S. and H.-Y. Chun, 2006: A Lagrangian spectral parameterization of gravity wave drag induced by cumlus convection. J. Atmos. Sci. (in revision).