Research in Engineering and Aviation
Effects of Hemispheric Circulation on Uranian Atmospheric Dynamics and Methane Depletion
Author(s): Warning, S.W., R.P. LeBeau, Cs. Palotai, and X. Deng
Effects of Hemispheric Circulation on Uranian Atmospheric Dynamics and Methane Depletion. 4th AIAA Atmospheric and Space Environments Conference, AIAA-2012-2931, New Orleans, LA, June 26. DOI: 10.2514/6.2012-2931
The solar system is filled with meteorological phenomena. For example, geophysical vortices range from hurricanes to the Great Red Spot on Jupiter to the Dark Spots of Uranus and Neptune. These Ice Giant vortices have exhibited unusual dynamical behaviors, such as the shape oscillations and meridional drift of the Great Dark Spot, discovered and observed in 1989 by Voyager II. On the other hand, the Uranian Dark Spot exhibited little to no drift over a similar stretch of observation when it appeared shortly before the spring equinox on Uranus in 2006. Another phenomenon is regions of persistent clouds, common in the banding patterns of the gas giants. The bright companion of the Great Dark Spot is a different type of persistent cloud, arising orographically as the vortex moved through the atmosphere. The Uranian Dark Spot may also have had a similar, although intermittent, cloud companion. Another notable long-lived cloud feature called S34 or the “Berg” in the southern hemisphere of Uranus, which drifted equatorward covering approximately 30 degrees in latitude over the course of a few years as equinox approached, having previously spent several years in the vicinity of 34 degrees south latitude. While this motion resembles in some ways that of the Great Dark Spot and its Bright Companion, there was no visible vortex associated with the Berg’s cloud. A proposed cause of this unexpected drift is the development of a strong meridional, Hadley-cell circulation that caused the cloud (and a possible unseen companion vortex) to drift equatorward. This same circulation may account for observations that showed upper tropospheric methane gas (a primary cloud constituent on Uranus) in the southern hemisphere was preferentially accumulating near the equator while depleting near the south pole. This paper presents the first efforts to examine these phenomena by numerically modeling a full Uranian atmosphere. These simulations are designed to examine these changes in the Uranian atmosphere, probably related to the extreme seasonal change of this planet. While this research will improve our understanding of the Uranian atmosphere and the design of future missions to this system, it will also assist in understanding the similar dynamics on the other Ice Giant planet Neptune, and potentially with similar phenomena in Earth’s atmosphere like hurricane drift.