Observed connections between apparent polar cap features and the instantaneous diffuse auroral oval |
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| Authors: | JS Murphree LL Cogger |
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| Institution: | The University of Calgary, Physics Department, Calgary, Alberta, Canada, T2N 1N4 |
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| Abstract: | Images of the instantaneous nightside auroral distribution reveal that at times the orientation of auroral oval arcs changes to become characteristic of polar cap arcs. These connecting arcs all terminate in the diffuse aurora in the midnight sector, and their separation from the equatorward boundary of the diffuse aurora generally increases away from the midnight termination. The occurrence of these features requires a northward interplanetary magnetic field (positive Bz) as well as low magnetic activity. The existence of connecting arcs and the observation that they are at times the poleward boundary of weak diffuse emission indicate that the poleward boundary of auroral emissions can be significantly modified during non-substorm periods. Such a distortion implies that there can be a modification of the standard convection pattern in the magnetosphere during periods of positive Bz to produce expanded regions of sunward convection in the high latitude ionosphere. |
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