Spontaneous Gravity Wave Radiation and Its Impact on the Venusian Super-rotation: Insights from Ultra-High Resolution GCM Simulations

Gravity waves play an essential role in planetary atmospheres by transporting momentum and energy far from their source regions. While observed in the Venusian atmosphere, their specific characteristics and generation mechanisms have remained poorly understood. This study investigates the activities of small-scale gravity waves using a Venus general circulation model with ultra-high spatial resolution (horizontal and vertical grid intervals of less than 20 km and 0.25 km, respectively).

Our simulations reveal that gravity waves are spontaneously radiated from nearly balanced flows as the super-rotation evolves. In the low-latitudes, thermal tides within the super-rotation act as the primary sources, whereas baroclinic and barotropic waves are essential sources in the mid- to high-latitudes. To isolate these mechanisms, we conducted experiments excluding the diurnal component of solar heating and performed sensitivity tests on the static stability of the cloud layer. We found that higher static stability weakens gravity wave radiation, indicating that the intensity of baroclinic instability is directly linked to the amount of spontaneous wave generation.

These small- to medium-scale gravity waves significantly affect the three-dimensional structure of the super-rotation and contribute to material mixing through their breaking processes. Notably, we confirmed for the first time that gravity waves in mid- to high-latitudes can transport zonal momentum vertically down to the lower atmosphere (~50–60 km). Furthermore, vertical propagation leads to a dual effect on the super-rotation: a deceleration in the upper cloud layer (~70 km) and an acceleration above ~80 km. These results demonstrate that momentum transport via spontaneous gravity wave radiation is a critical component of the Venusian atmospheric circulation and must be accounted for in our understanding of its global dynamics.