Motion of polar cap patches: A statistical study with all‐sky airglow imager at Resolute Bay, Canada

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Abstract
A highly sensitive all‐sky airglow imager (part of the Optical Mesosphere Thermosphere Imagers [OMTIs]) has been operating for 3 years at Resolute Bay, Canada (geographic latitude 74.7°N; geomagnetic latitude 82.9°N) since January 2005. One of its major applications is the observation of polar cap patches. Polar cap patches are generated in the vicinity of the cusp during southward interplanetary magnetic field (IMF) conditions, and they exhibit dynamic movement, possibly in association with the changes in the IMF orientation. In order to determine how their motions are controlled by the upstream IMF conditions, we applied a motion‐tracking algorithm that was based on two‐dimensional cross‐correlation analysis to consecutive images obtained from January 2005 to December 2007 by the all‐sky airglow imager at Resolute Bay. We identified and extracted 561 individual patches and then carried out a statistical study of their motion. It is demonstrated that the speed of patches is primarily controlled by the IMF Bz. Furthermore, the dawn‐dusk component of the patch drift velocities is well correlated with the IMF By, which is in good agreement with the published By dependence of the nightside polar cap convection. This enables us to monitor the plasma convection within the polar cap by using polar cap patches as tracers.

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