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Field-Line Resonances Triggered by a Northward
IMF Turning

H. Laakso,1, D. H. Fairfield,2 C. T. Russell,3 J. H. Clemmons,4 H. J. Singer,5 B. L. Giles,6 R. P. Lepping,2
F. S. Mozer,7 R. F. Pfaff,2 K. Tsuruda,8 and J. R. Wygant9

Received October 16, 1997, revised January 5, 1998, accepted February 4, 1998


A sudden northward rotation of the IMF observed by IMP 8 near the bow shock at 21:22 UT on January 10, 1997, triggered surface waves and fast mode waves at the flanks of the duskside magnetosphere, as observed by GEOTAIL instruments. The power spectral density of these waves peaked in the frequency range where field-line resonances were observed by the POLAR satellite in the region L = 6.6-10.2. The oscillation periods of the observed field-line resonances were L-dependent with two distinct peaks which may be explained by increased heavy ion content at those field lines. The ULF waves also caused enhanced low-energy ion fluxes from the ionosphere.

1Finnish Meteorological Institute, Helsinki, Finland.
2NASA Goddard Space Flight Center, Greenbelt, MD.
3Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA.
4Aerospace, Los Angeles, CA.
5Space Environment Center, NOAA, Boulder, CO.
6NASA Space Flight Center, Huntsville, AL.
7Space Sciences Lab., Univ. California, Berkeley, CA.
8ISAS, Sagamihara, Japan.
9School of Physics and Astronomy, University of Minnesota, Minneapolis, MN.

© 1998 by the American Geophysical Union.
Paper number 98GL51034.

© 1998 AGU

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