Cusp aurora dependence on interplanetary magnetic field Bz

S. A. Fuselier
Lockheed Martin Advanced Technology Center,
Palo Alto, California, USA

H. U. Frey
Space Sciences Laboratory, University of California,
Berkeley, California, USA

K. J. Trattner
Lockheed Martin Advanced Technology Center,
Palo Alto, California, USA

S. B. Mende
Space Sciences Laboratory, University of California,
Berkeley, California, USA

J. L. Burch
Southwest Research Institute,
San Antonio, Texas, USA


The Imager for Magnetopause to Aurora Global Exploration (IMAGE) Spectrographic
Imager (SI12) detects Doppler-shifted Lyman alpha emissions created by charge
exchange and de-excitation of precipitating protons in the atmosphere. At high
latitudes near local noon, emissions consistent with the location of the cusp
foot point have distinct interplanetary magnetic field (IMF) dependence. For
northward IMF a spot of emissions is observed poleward of the dayside auroral
oval. By tracing the magnetic field lines from this spot using a model
magnetosphere it is shown that the cusp foot point maps to a narrow region on
the high-latitude magnetopause where antiparallel magnetic reconnection is
likely to be occurring. As the IMF turns southward, the spot merges into the
auroral oval, producing a broad region of intense emissions centered near local
noon. By tracing the magnetic field lines from this broad region using a model
magnetosphere it is shown that the cusp foot point maps to a relatively broad
region on the dayside magnetopause where component magnetic reconnection may be
occurring. 

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J. Geophys. Res., 107, A7, 2002.