CHARACTERISTICS OF FINITE-AMPLITUDE STATIONARY GRAVITY-WAVES IN THE ATMOSPHERE OF VENUS

This paper extends the study of stationary gravity waves generated nea r the surface of Venus reported previously by Young et al. to include finite amplitude effects associated with large amplitude waves. Waves are forced near the surface of Venus by periodic forcing. The height-d ependent profiles of static stability and mean wind in the Venus atmos phere play a very important role in the evolution of the nonlinear beh avior of the waves, just as they do in the linear wave solutions. Cert ain wave properties are qualitatively consistent with linear wave theo ry, such as wave trapping, resonance, and wave evanescence for short h orizontal wavelengths. However, the finite amplitude solutions also ex hibit many other interesting features. In particular, for forcing ampl itudes representative of those that could be expected in mountainous r egions such as Aphrodite Terra, waves generated near the surface can r each large amplitudes at and above cloud levels, with clear signatures in the circulation pattern. At still higher levels, the waves can rea ch large enough amplitude to break, unless damping rates above the clo uds are sufficient to lin-tit wave amplitude growth. Well below cloud levels the waves develop complex flow patterns as the result of finite amplitude wave-wave interactions, and waves are generated having cons iderably shorter horizontal wavelengths than that associated with the forcing near the surface. Nonlinear interactions can excite waves that are resonant with the background wind and static stability fields eve n when the primary surface forcing does not, and these waves can domin ate the wave spectrum near cloud levels. A global map of Venus topogra phic slopes derived from Magellan altimetry data shows that slopes of magnitude comparable to or exceeding that used to force the model are ubiquitous over the surface.