HR: 0800h
AN: SH12A-0849    [Abstracts]
TI: Directional ENA Flow in the Earth's Magnetosheath: Estimation of the Magnetopause Subsolar Distance
AU: * Nishizawa, R
EM: nishizawa@ice.uec.ac.jp
AF: Univ. of Electro-Communications, 1-5-1 Chofugaoka, Chofu/Tokyo, 182-8585, Japan
AU: Taguchi, S
EM: taguchi@ice.uec.ac.jp
AF: Univ. of Electro-Communications, 1-5-1 Chofugaoka, Chofu/Tokyo, 182-8585, Japan
AU: Hosokawa, K
EM: hosokawa@ice.uec.ac.jp
AF: Univ. of Electro-Communications, 1-5-1 Chofugaoka, Chofu/Tokyo, 182-8585, Japan
AU: Collier, M R
EM: michael.r.collier@nasa.gov
AF: NASA/GSFC, Code 673, Greenbelt, MD 20771, United States
AU: Moore, T E
EM: thomas.e.moore@gsfc.nasa.gov
AF: NASA/GSFC, Code 673, Greenbelt, MD 20771, United States
AB: Recent studies with the low-energy neutral atom imager (LENA) on the IMAGE spacecraft have shown that directional ENAs are emitted in the Earth's magnetosheath flow through charge exchange with the Earth's hydrogen exosphere. In order to obtain the subsolar distance of the magnetopause from the LENA observation we have modeled ENA flux distributions using the gasdynamic theory for magnetosheath ions and the hydrogen exospheric density model, and compared with the observations. The line of sight integration of the distribution of the ENA flux starting at a relatively high-latitude point inside the magnetosphere with arbitrary dimension shows that the distribution has a clear peak in the direction looking into the low-latitude magnetosheath, which is consistent with the LENA observation in the near-noon sector. By adapting the direction of the peak emission in the model to the one in the LENA observation, we have calculated the subsolar distance. The test for several cases shows that the magnetopause inward motion triggered by the sharp increase of the solar wind dynamic pressure can be taking place during several minutes. Simultaneous observations from in-situ GOES 8 are consistent with this result. This approach thus opens a new way of the empirical modeling of the response of the subsolar distance for the sharp solar wind variation, which was estimated from previous empirical models based on in-situ spacecraft observations to be instantaneous.
DE: 2151 Neutral particles (7837)
DE: 2724 Magnetopause and boundary layers
DE: 2728 Magnetosheath
DE: 2784 Solar wind/magnetosphere interactions
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2007 Fall Meeting