Incorporation of a Gravity Wave Momentum Deposition Parameterization into the VTGCM

The National Center for Atmospheric Research (NCAR) thermospheric general circulation model for Venus (VTGCM) is a three dimensional model that can calculate temperatures, zonal winds, meridional winds, vertical winds, and concentration of specific species. The calculated nightside warm region (near ~100 km) and the O₂-IR and NO-UV nightglow intensity distributions have been produced to represent mean conditions observed by Venus Express data and ground-based observations with the use of Rayleigh friction (Brecht et al. JGR, 2011). Rayleigh friction is implemented to parameterize gravity wave momentum drag effects on the global mean zonal wind flow. The purpose is to obtain a first order approximation of the necessary drag to reproduce observations. In addition, Rayleigh friction provides guidelines for the implementation and adjustment of a gravity wave momentum deposition scheme. Most recently, the Alexander and Dunkerton (AMS, 1999) gravity wave momentum parameterization has been incorporated into the VTGCM. The parameterization is designed to deposit momentum fluxes locally and totally at the altitude of wave breaking. Further, it allows waves to continue to propagate above the breaking altitude. Specific fields will be shown to illustrate the impacts the parameterization has on the global circulation (i.e. temperatures, zonal winds, and night airglow distributions (O₂ IR and NO UV)). In addition, the chosen values for parameters will be discussed and their importance for depositing the gravity wave momentum. The gravity wave momentum parameterization launches waves from the cloud region within the VTGCM and provides a strong source for asymmetrical global winds.