Magnetosphere - Ionosphere Coupling: Sub-auroral Heating of the Topside Ionospheric Electrons C. Gurgiolo (1) , B. R. Sandel (2), J. D. Perez (3), D. G. Mitchell (4), C. J. Pollock (5), and B. A. Larsen (6) (1) Bitterroot Basic Research Inc., 837 Westside Road, Hamilton, MT 59840, USA (chris@gurgiolo.com) (2) Lunar and Planetary Laboratory, The University of Arizona, Sonett Space Sciences Building, 1541 East University Boulevard, Tuscon, AZ 85721-0063, USA (3) Physics Department, Auburn University, Auburn, AL 36849, USA (4) Applied Physics Laboratory, Johns Hopkins University, Johns Hopkins Road, Laurel, MD 20723, USA (5) Southwest Research Institute, P. O. Drawer 28510, San Antonio, TX 78228-0510, USA (6) Department of Physics, Space Science and Engineering Laboratory, P. O. Box 173840, Montana State University, Bozeman, MT 59717-3840, USA The overlap of the ring-current with the outer plasmasphere is thought to play a major roll in the observations of storm-time related in-creases in the sub-auroral ambient topside electron temperatures. Instabil-ities generated within the overlap region, Coulomb collisions of plasmaspheric electrons with the ring-current ions, and charge exchange are all thought to work either individually or together to generate a downward directed heat ux which produces the increase in temperature. Which of these processes, if any, plays the more dominant role in the magnetospheric-ionospheric cou-pling has been the topic of many papers. The purpose of this paper is to present the first set of global, simultaneous observations of the ring-current and plasmasphere during storm time conditions together with in-situ measurements of the local topside ionospheric ambient electron temperature. ________________ Journal of Geophysical Research, in press, 2005