UV-Dark Polar Ovals on Jupiter: Tracing the Depth of the Magnetosphere-Atmosphere Connection
Date:
Talk at Magnetospheres in the Outer Solar System II Session, AGU Fall Meeting, San Francisco, CA
Abstract
The interactions between Jupiter’s magnetosphere and upper atmosphere are an essential component of the dynamics of both systems, but these interactions are typically discussed where the ionospheric densities are highest, above a microbar. Past measurements of aurorally associated heating are seen as deep as 1 mbar, influencing stratospheric composition. Here, we report on a southern UV-dark oval (SUDO) within Jupiter’s southern auroral region, revealing auroral interactions far deeper into the atmosphere at around 20 mbar.
Via a systematic analysis of 25 epochs of archived data from the Hubble Space Telescope between 1994 and 2022, we measure a 50 to 80% occurrence rate of the SUDO, which is 3 to 10 times more frequent than its northern counterpart. All but one detection lies inside the main auroral oval. The sense of rotation is anticyclonic, similar to the behavior of the northern dark oval seen by Cassini (Porco et al. 2003, Science, DOI 10.1126/science.1079462). The location of the SUDO within the auroral oval, along with its anticyclonic rotation, suggests a magnetospheric connection.
Sub-Keplerian drag in the magnetosphere drives an anticyclonic vortex as field lines stir up the thermosphere (Wang et al. 2023, submitted). When this flow penetrates into the stratosphere, we hypothesize that the momentum input affects the aerosol distribution, enabling transient visibility of a SUDO. We highlight how these deep atmospheric flows may have important implications for how effectively Jupiter’s atmosphere can carry magnetospherically driven currents. However, the precise dynamical picture remains unclear. A constrained radiative transfer analysis based on the results of Zhang et al. (2013, Icarus, DOI 10.1016/j.icarus.2013.05.020) suggests that SUDO contrast can be explained by a 20 to 50 times increase in stratospheric haze abundance. The smaller size of the southern aurora and its closer alignment to the jovigraphic pole may allow thermospheric winds to penetrate more deeply in the south, explaining the increased frequency of the southern oval compared to its northern counterpart. Further study of this transient dark oval would provide unique insight into the connection between the magnetosphere, thermosphere, and stratosphere in the jovian poles.