SIMULATION OF THE MORPHOLOGY OF THE JOVIAN UV NORTH AURORA OBSERVED WITH THE HUBBLE-SPACE-TELESCOPE

A model simulating Earth views of UV auroral arcs and diffuse emission s in the Jovian north polar region is described. It assumes a Chapman profile of vertical brightness distribution and various horizontal str uctures, Simple geometric cases are described to illustrate the depend ence on the altitude, atmospheric scale height, and central meridian p lanetary longitude (CML) of an idealized amoral morphology seen from E arth orbit, The numerical simulation makes it possible to assess the i mportance 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 use d to determine the characteristics of their auroral (discrete and diff use) structures, The apparent brightness distribution along the arcs c an only be reproduced if intrinsic longitudinal (or local time) variat ions are introduced, in addition to the path length effects of the vie wing geometry, A composite average auroral distribution is built by ma pping 10 WFPC2 images from the same dataset, It illustrates the dichot omy frequently observed between a narrow single structure are at Syste m III longitudes larger than 180 degrees (or morning sector) and the m ultiple are and broad diffuse emission at longitudes less than 180 deg rees (or afternoon sector), It is shown that the equatorial auroral em ission boundary is located between the 6R(J) and the 30R(J) magnetic h eld line footprints of the Goddard Space Flight Center (GSFC) O-6 mode l. (C) 1997 Academic Press.