HR: 10:35h
AN: SH52B-02    [Abstracts]
TI: The Spatial Distribution of Upstream Ion Events Measured by ACE, Wind, and STEREO Near the Earth's Bow Shock
AU: * Desai, M I
EM: mdesai@swri.edu
AF: Southwest Research Institute, 6200 Culebra Road, San Antonio, TX 78238, United States
AU: Mason, G M
EM: glenn.mason@jhuapl.edu
AF: Applied Physics Laboratory, The Johns Hopkins University, Laurel, MD 20724, United States
AU: Muller-Mellin, R
EM: mueller-mellin@physik.uni-kiel.de
AF: Christian-Albrechts-Universitat Zu Kiel, Leibnizstrasse 11, Kiel, 24118, Germany
AU: Smith, C W
EM: chuck@briaxa.sr.unh.edu
AF: University of New Hampshire, Department of Physics and Space Science Center, Durham, NH 03824, United States
AB: Abrupt enhancements in the intensities of ions in the energy range of a few 10s of keV to 100s of keV upstream of the Earth's Bow Shock –- upstream ion events –- are characterized by short durations (~1-2 hours), steeply falling spectra, large (>100:1) field-aligned sunward anisotropies, and positive correlations with the solar wind speed and geomagnetic indices. Despite the wealth of information available, however, it is still not clear whether these ions are accelerated at the bow shock or somewhere inside the Earth's magnetosphere. Furthermore, such events are also often observed simultaneously at two or more spacecraft, perhaps indicating that a large source region covering the entire size of the bow shock fills large spatial structures in the upstream region. In this paper we use simultaneous measurements of >40 keV upstream ions observed at ACE, Wind, and STEREO-A between 2007, day 1 through 2007, day 181 to calculate the occurrence probability of upstream events as a function of lateral and radial separation between L1 and STEREO-A. During the end of this ~6- month period, Wind (or ACE) and STEREO-A were separated by ~1750 R_E in the radial direction and laterally in Y_GSE by ~3800 R_E. Despite this large separation, STEREO-A continued to observe upstream events right up until the end of our survey period. More surprisingly, we found that the occurrence probability for measuring simultaneous upstream events at Wind or ACE at L1 and STEREO-A was ~20- 30%, i.e., far greater than that expected from accidental coincidences. We discuss the implications of these results for the size of the source region, the conditions under which upstream events occur, and the size and nature of the spatial structures in which these ions populate and propagate in the upstream region.
DE: 2114 Energetic particles (7514)
DE: 2134 Interplanetary magnetic fields
DE: 2154 Planetary bow shocks
DE: 2784 Solar wind/magnetosphere interactions
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2007 Fall Meeting