Local properties of the reconnecting magnetotail current sheet: a statistical study using Geotail and Cluster

Abstract:

Reconnection in the near-Earth magnetotail occurs most frequently duskward of midnight. This asymmetry is evident in the spatial occurrence of both reconnection- driven transients and of the reconnection site itself. From a number of studies that investigated the cause of this asymmetry, there are two main, opposing explanations: ‘global’ and ‘local’. The ‘global’ explanation is that asymmetric ionospheric conductance is the cause. The ‘local’ explanation points to the asymmetric thinning of the plasma sheet as the cause of the asymmetry. A number of observational studies have identified the effects of the ‘local’ and ‘global’ controls of the properties of the non-reconnecting magnetotail current sheet. In this study, we analyze the properties of the reconnecting current sheet (in the vicinity of an active reconnection site) using in situ data from Geotail and Cluster encounters with the reconnection site. Our method is specific to the geometry of the current sheet crossing for either Geotail or Cluster. For all of our observations, we approximate the current sheet with the Harris model. For Cluster data, we use a modified curlometer technique to analyze the strength and profile of the ion-scale current. For Geotail data, our analysis technique depends on whether the encounter with the reconnection site was driven by the motion of the current sheet or the motion of the spacecraft. We compare the properties of the current sheet for reconnection observations near the dawn and dusk flanks (infrequent) with those for reconnection observations on the near-midnight duskside (more frequent). Initial results are presented.