Orographic Cloud Development Paired with Atmospheric Vortex Dynamics on Uranus and Neptune

摘要

Large geophysical vortices provide some of the most dramatic atmospheric features in the solar system. Common examples include terrestrial hurricanes and the Great Red Spot of Jupiter, but similar vortex features on the Ice Giants of Uranus and Neptune are not as well known. Several vortices, known as Dark Spots for their relatively darker blue coloration compared to the background atmosphere, have appears on these planets. The most notable and best-observed remains the original Great Dark Spot discovered by Voyager II in 1989. Through eight months of observation the spot drifted towards the equator by ten degrees in latitude and oscillated in shape over an eight-day period during the month of closest observation. However, the Great Dark Spot was not alone, accompanied by persistent orographic methane clouds known as the Bright Companion. Such cloud-vortex pairings have repeated with other dark spots in the past two decades, indicating that they are a recurring feature of these atmospheres. In at least recent case, such a pairing may only be visible due to its cloud features, with the vortex generating no appreciable background contrast. Numerical research on these features suggests that the clouds influence the dynamics of these systems, and as such are critical to understanding the physics governing the vortex motions.