Simulation of the Morphology of the Jovian UV North Aurora Observed with the Hubble Space Telescope

Abstract

A model simulating Earth views of UV auroral arcs and diffuse emissions in the Jovian north polar region is described. It assumes a Chapman profile of vertical brightness distribution and various horizontal structures. Simple geometric cases are described to illustrate the dependence on the altitude, atmospheric scale height, and central meridian planetary longitude (CML) of an idealized auroral morphology seen from Earth orbit. The numerical simulation makes it possible to assess the importance of limb brightening and the contribution from high altitude auroral emission located behind the planetary limb. As an application of the simulation model, four images obtained with the Wide Field and Planetary Camera 2 (WFPC2) on board the Hubble Space Telescope are used to determine the characteristics of their auroral (discrete and diffuse) structures. The apparent brightness distribution along the arcs can only be reproduced if intrinsic longitudinal (or local time) variations are introduced, in addition to the path length effects of the viewing geometry. A composite average auroral distribution is built by mapping 10 WFPC2 images from the same dataset. It illustrates the dichotomy frequently observed between a narrow single structure arc at System III longitudes larger than 180° (or morning sector) and the multiple arc and broad diffuse emission at longitudes less than 180° (or afternoon sector). It is shown that the equatorial auroral emission boundary is located between the 6R_Jand the 30R_Jmagnetic field line footprints of the Goddard Space Flight Center (GSFC) O₆model.