Atmospheric Circulation on Venus

Abstract Venus is a slowly rotating planet with a thick atmosphere (~9.2 MPa at the surface). Ground- and satellite-based observations have shown atmospheric superrotation (atmospheric rotation much faster than solid surface rotation), global-scale cloud patterns (e.g., Y-shaped and bow-shaped structures), and polar vortices (polar hot dipole and fine structures). The Venusian atmospheric circulation, controlled by the planet’s radiative forcing and astronomical parameters, is quite different from the earth’s. As the meteorological data have been stored, understanding of the atmospheric circulation has been gradually enriched with the help of theories of geophysical fluid dynamics and meteorology. In the cloud layer far from the surface (49–70 km altitude), superrotational flows (east-to-west zonal winds) exceeding 100 m/s and meridional (equator-to-pole) flows have been observed along with planetary-scale brightness variations unique to Venus. The fully developed superrotation, which is ~60 times faster than the planetary rotation, is maintained by meridional circulation and waves. For the planetary-scale variations, slow-traveling waves with stationary and solar-locked structures and fast-traveling waves with phase velocities of around the superroational wind speeds are dominant in the cloud layer. Thermal tides, Rossby waves, Kelvin waves, and gravity waves play important roles in mechanisms for maintaining fast atmospheric rotation. In the lower atmosphere below the cloud layer, the atmospheric circulation is still unknown because of the lack of global observations. In addition to the limited observations, the atmospheric modeling contributes to deep understanding of the atmospheric circulation system. Recent general circulation models have well simulated the dynamical and thermal structures of Venus’s atmosphere, though there remain outstanding issues.