LENA Observations on March 31, 2001: Magnetosheath Remote Sensing

Michael R Collier 1 (301-286-5256; mcollier@pop600.gsfc.nasa.gov)
Thomas E Moore 1 (301-286-5236; thomas.e.moore@gsfc.nasa.gov)
Mei-Ching Fok 1 (mei-ching.fok@gsfc.nasa.gov)
Dennis Chornay 1 (dennis.chornay@gsfc.nasa.gov)
Lutz Rastaetter 1 (lr@waipio.gsfc.nasa.gov)
Masha Kuznetsova 1 (mkuznets@pop600.gsfc.nasa.gov)
Ayris Falasca 1 (ayris.a.falasca.1@gsfc.nasa.gov)
James Green 1 (green@ndadsb-f.gsfc.nasa.gov)
Scott Boardsen 1 (boardsen@xfiles.gsfc.nasa.gov)
Stephen Fuselier 2 (fuselier@mail.spasci.com)
Steve Petrinec 2 (petrinec@mail.spasci.com)
Michelle Thomsen 3 (mthomsen@nis-pop.lanl.gov)
David McComas 4 (dmccomas@swri.edu)
Tamas I Gombosi 5 (tamas@umich.edu)

1 NASA Goddard Space Flight Center, Space Sciences Directorate,
  Greenbelt, MD 20770, United States
2 Lockheed Martin Advanced Technology Center, Space Physics Lab 3251 Hanover St.,
  Palo Alto, CA 94304-1191, United States
3 Los Alamos National Laboratory, Space and Atmospheric Science (NIS-1) MS D466,
  Los Alamos, NM 87545, United States
4 Southwest Research Institute, Space Science and Engineering Division,
  San Antonio, TX 78228, United States
5 University of Michigan, Department of Engineering, Ann Arbor, MI 48109,
  United States

We discuss observations from the IMAGE Low Energy Neutral Atom (LENA)
imager on March 31, 2001 when the solar wind flux, as measured by
ACE/SWEPAM, was over a factor of ten higher than typical solar wind
conditions. Observations from LANL-94 on this day indicate that over the
time period of interest, about 0330-0600 UT, the magnetopause was inside
of geosynchronous orbit. The flux of neutrals resulting from solar wind
charge exchange with the Earth's geocorona scales with the product of:
(1) solar wind flux, (2) geocoronal density, (3) line of sight
integration length, and (4) the reciprocal of the square of the source
distance. Because all of these factors increase dramatically with high
solar wind flux, LENA observes significant brightening between the
direction of the Sun and the Earth on this day. These emissions are a
continuous non-linear function of solar wind flux, varying as the solar
wind flux to about the 3.7 power. They cannot be explained by a LENA
response to energetic charged particles. The LENA data have been
compared to results of global MHD simulations performed at the Community
Coordinated Modeling Center (CCMC) using the BATSRUS global MHD code
developed at the University of Michigan for this day. The comparison
shows that solar wind charge exchange with the Earth's geocorona will
produce the signal observed by LENA. Furthermore, structure in the LENA
observations can be mapped to features appearing in the CCMC
simulations, suggesting that plasma structure in the magnetosheath may
be imaged using low energy neutral atom line-of-sight profiles.