FAST/Geotail Observations of Magnetosphere-Ionosphere Coupling

C. A. Cattell, K. Sigsbee (School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455)

C. W. Carlson, R. E. Ergun, J. P. McFadden, F. Mozer, W. Peria (Space Sciences Laboratory, University of California, Berkeley, CA 94720)

R. C. Elphic (Space and Atmospheric Sciences, Los Alamos National Lab, Los Alamos, NM 87545)

R. J. Strangeway (Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90024)

K. Tsuruda and T. Yamamoto (ISAS, Sagamihara 229, Japan)

S. Kokubun (STELAB, Nagoya University, Toyokawa 442, Japan)

D. Fairfield (NASA/GSFC, Laboratory for Extraterrestrial Physics, Code 695, Greenbelt, MD 20771)

G. Parks, M. Brittnacher (University of Washington)

During 1997, a number of conjunctions between the FAST and Geotail satellites occurred where FAST was in the nightside auroral zone and Geotail was close to midnight in the near equatorial plane. Additional conjunctions occurred at other local times. Some of these events had additional conjunctions including Polar imaging, Wind in the near midnight magnetotail, and Polar at or near the plasma sheet boundary. These events provide an excellent opportunity to examine the physical processes connecting the magnetotail at 20 to 40 earth radii and the auroral zone during substorms and quiet times. Comparisons of waves observed by Geotail and FAST have provided evidence for magnetosphere- ionosphere coupling via Alfven waves, as well as the near simultaneous occurrence of waves in other frequency bands. The dominant wave modes will be identified and their implications for relevant substorm processes will be discussed. For one event, examination of the density (as determined by the spacecraft potential) observed by Polar and Geotail has indicated the large-scale nature of plasma sheet expansion. We will describe the available data sets, and discuss results from specific event studies to elucidate aspects of magnetosphere-ionosphere coupling processes.