Conditions governing localized high-latitude dayside aurora

H. Korth, B. J. Anderson, H. U. Frey, T. J. Immel, S. B. Mende


In a recent study of IMAGE FUV data, Frey et al. [2003] examined cases of
high-latitude dayside aurora (HiLDA) caused by precipitating electrons
predominantly during northward IMF with a strongly positive IMF B y component.
To determine the conditions that control these auroral emissions, we examine
field-aligned currents observed by the Iridium constellation for 25 events of
prolonged steady IMF orientation with both B z and B y positive. We find that
localized FACs are sustained under all observed solar wind conditions, but that
the occurrence of HiLDA is generally restricted to solar wind proton densities
below 4 cm-3 and peak current densities higher than 0.7 mu A/m2. That the solar
wind density orders the occurrence of the auroral emissions indicates that
magnetosheath plasma has ready access to the field lines carrying the upward
current. Assuming that the magnetosheath plasma density and temperature govern
the high-altitude conditions on these field lines, we find that the intensity of
the HiLDA emissions correlates with an estimate for the particle precipitation
energy density based on the Knight relation, using the measured current density
and the magnetosheath temperature and density.

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Geophysical Research Letters, 31, L04806, doi:10.1029/2003GL018911, 2004