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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. A11, 1362, doi:10.1029/2002JA009245, 2002

Solar wind dependence of the occurrence and motion of polar auroral arcs: A statistical study

A. Kullen

Royal Institute of Technology, Alfvén Laboratory, Stockholm, Sweden


M. Brittnacher

Department of Earth and Space Sciences, University of Washington, Seattle, Washington, USA


J. A. Cumnock

Royal Institute of Technology, Alfvén Laboratory, Stockholm, Sweden


L. G. Blomberg

Royal Institute of Technology, Alfvén Laboratory, Stockholm, Sweden


Abstract

Polar UV images from a 3-month period in winter 1998–1999 are used for a statistical study of polar arcs. The study covers all auroral arcs that are located poleward of the northern auroral oval, and which are detectable by the UV imager. The arcs are examined with respect to their spatial and temporal behavior as well as to a possible connection to solar wind parameters using ACE satellite data. It is found that the majority of polar arcs appear during northward IMF, strong IMF magnitude, and high solar wind speed. A modified Akasofu-Perreault epsilon parameter with a cosine function instead of a sine function (vB2 cos4(θ/2)(l02/μ0)) combines these results. It correlates well with the occurrence frequency of polar arcs for long timescales. The location of polar arcs is strongly dependent on the sign of the IMF By component. Static polar arcs occur in the Northern Hemisphere on the dawn (dusk) side of the oval for negative (positive) IMF By, whereas poleward-moving arcs separate from the opposite side of the oval, and then move in the direction of IMF By. All polar arcs are sorted into five different categories according to their spatial structure and evolution: oval-aligned, bending, moving, midnight, and multiple arcs. Each polar arc type occurs for a characteristic combination of solar wind parameters. IMF clock angle changes seem to have a strong influence on what type of arc occurs. Oval-aligned arcs appear mainly during steady IMF, bending arcs after an IMF Bz sign change, and moving arcs after an IMF By sign change. For the rare midnight and multiple arc events, no characteristic IMF clock angle dependence has been found. The different types of clear polar arcs are discussed in the context of existing observational studies and transpolar arc models.

Published 14 November 2002.

Index Terms: 2475 Ionosphere: Polar cap ionosphere; 2736 Magnetospheric Physics: Magnetosphere/ionosphere interactions; 2784 Magnetospheric Physics: Solar wind/magnetosphere interactions; 2776 Magnetospheric Physics: Polar cap phenomena.

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Citation: Kullen, A., M. Brittnacher, J. A. Cumnock, and L. G. Blomberg (2002), Solar wind dependence of the occurrence and motion of polar auroral arcs: A statistical study, J. Geophys. Res., 107(A11), 1362, doi:10.1029/2002JA009245.