Large‐scale high‐latitude dayside auroral emissions

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Abstract
Observations made with the Viking UV imager reveal that on the dayside of the auroral distribution there often occur emission features poleward of the normal continuous auroral distribution when the interplanetary magnetic field (IMF) is northward and in an away garden hose configuration. The position of these features, while consistent with the expected location of cusp aurora, does not exhibit the strictly diffuse character of cusp emissions which is generally the signature of direct magnetosheath particle access. Further the strong IMF dependence tends to suggest a separate auroral process from that which results in the discrete features commonly found in the cleft region. This coupled with the observation that large‐scale polar arcs are seen to frequently connect to these dayside features argues that in fact these auroral emission features are the result of processes occurring on the front surface of the magnetotail (i.e., on the magnetopause poleward of the cusp). This is consistent with the discovery that these features seem to exist predominantly when the IMF By component is positive, Bx negative, and Bz is northward, which implies that merging on the front surface of the magnetotail is involved in producing these emissions. Evidence is presented which distinctly links the location of merging lines due to dipole tilt and magnetic activity with the location of these high‐latitude dayside features.