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JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 112,
A11208,
doi:10.1029/2007JA012404,
2007
Correlative variations of the neutral atom emission in the high-altitude cusp and the fast anti-sunward convection in the
low-altitude cusp
Y. Murata
Sugadaira Space Radio Observatory, University of Electro-Communications, Tokyo, Japan
S. Taguchi
Department of Information and Communication Engineering, University of Electro-Communications, Tokyo, Japan
K. Hosokawa
Department of Information and Communication Engineering, University of Electro-Communications, Tokyo, Japan
A. Nakao
Department of Information and Communication Engineering, University of Electro-Communications, Tokyo, Japan
M. R. Collier
NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
T. E. Moore
NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
N. Sato
National Institute of Polar Research, Tokyo, Japan
H. Yamagishi
National Institute of Polar Research, Tokyo, Japan
A. S. Yukimatu
National Institute of Polar Research, Tokyo, Japan
Abstract
Recent studies have shown that the Low Energy Neutral Atom (LENA) imager on the IMAGE spacecraft in the magnetosphere detects
neutral atoms coming from the direction of the high-altitude cusp. The primary source of the neutral atoms has been reported
to be the entry of the ions in the cusp, but the evidence for this remains limited. Therefore we herein report the correlative
variations of the neutral atom signal in the direction of the high-altitude cusp and the fast anti-sunward convection in the
ionospheric cusp from an event of simultaneous observations from IMAGE/LENA and SuperDARN radar. During a period of IMF B Z of −40 to −10 nT on 11 April 2001, LENA on IMAGE at (X GSM, Y GSM, Z GSM) ∼ (4 R E, 0 R E, 4 R E) observed significant enhancements of neutral atom signals in the direction of the high-altitude cusp. In concurrence with
these enhancements, SuperDARN radars observed an increase in anti-sunward flow accompanied by equatorward shift of the polar
cap boundary. Detailed analyses of the SuperDARN velocity data reveal that the fast anti-sunward flow region widens and shrinks
longitudinally in correlation with the increase and decrease of the LENA signal, respectively. This correlation shows that
the neutral atom emission in the direction of the high-altitude cusp for southward IMF is due to the ion entry caused by enhanced
reconnection on the dayside magnetopause. Hence the present study provides evidence of the cusp ion injection being the primary
source of the LENA high-altitude cusp signal for the southward IMF.
Received 16
March
2007;
accepted 15
August
2007;
published 13
November
2007.
Keywords: Magnetosphere-ionsphere interactions;
cusp;
neutral atoms.
Index Terms: 2151 Interplanetary Physics: Neutral particles (7837); 2431 Ionosphere: Ionosphere/magnetosphere interactions (2736); 2712 Magnetospheric Physics: Electric fields (2411); 2463 Ionosphere: Plasma convection (2760); 2728 Magnetospheric Physics: Magnetosheath.
Read Full Article (file size: 629721 bytes) Cited by
Citation: Murata, Y., S. Taguchi, K. Hosokawa, A. Nakao, M. R. Collier, T. E. Moore, N. Sato, H. Yamagishi, and A. S. Yukimatu
(2007),
Correlative variations of the neutral atom emission in the high-altitude cusp and the fast anti-sunward convection in the
low-altitude cusp,
J. Geophys. Res.,
112,
A11208,
doi:10.1029/2007JA012404.
Copyright 2007 by the American Geophysical Union.
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