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Ann. Geophys., 22, 159-168, 2004
www.ann-geophys.net/22/159/2004/
© European Geosciences Union 2004
Origin of the SuperDARN broad Doppler spectra:simultaneous observation with Oersted satellite magnetometer
K. Hosokawa1, S. Yamashita2, P. Stauning3, N. Sato4, A. S. Yukimatu4, and T. Iyemori5
1Department Information and Communication Engineering, The University of Electro-Communications, Tokyo, Japan
2Department of Geophysics, Graduate School of Science, Kyoto University, Kyoto, Japan
3Danish Meteorological Institute, Copenhagen, Denmark
4National Institute of Polar Research, Tokyo, Japan
5Data Analysis Center for Geomagnetism and Space Magnetism, Graduate School of Science, Kyoto University, Kyoto, Japan
Abstract. We perform a case study of a favorable conjunction of an overpass of the Oersted satellite with the
field-of-view of the SuperDARN Syowa East radar during an interval of the southward IMF Bz. At
the time, the radar observed an L-shell aligned boundary in the spectral width around the dayside
ionosphere. Simultaneously, high-frequency (0.2–5Hz) magnetic field fluctuations were observed
by the Oersted satellite's high-time resolution magnetometer. These magnetic field fluctuations are
considered to be Alfvén waves possibly associated with the particle which precipitates into the
dayside high-latitude ionosphere when magnetic reconnection occurs. It has been theoretically
predicted that the time-varying electric field is the dominant physical process to expand the broad
HF radar Doppler spectra. Our observation clearly demonstrates that the boundary between narrow
and broad spectral widths is corresponding well to the boundary in the level of the fluctuations,
which supports the previous theoretical prediction. A close relationship between electric and
magnetic field fluctuations and particle precipitations during southward IMF conditions has
been confirmed by many authors. The present observation allows us to suggest that the boundary
between narrow and broad Doppler spectral widths observed in the dayside ionosphere is connected
with the signature of the open/closed field line boundary, such as the cusp particle precipitations
via electric and magnetic field fluctuations for the case of the negative IMF Bz conditions.
Key words. Ionosphere (ionosphere-magnetosphere interactions;
plasma convection). Magnetospheric physics (magnetopause,
cusp, and boundary layers)
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