Abstract
Abstract. We present space- and ground-based observations of the signatures of magnetic reconnection during an interval of duskward-oriented interplanetary magnetic field on 25 March 2004. In situ field and plasma measurements are drawn from the Double Star and Cluster satellites during traversals of the pre-noon sector dayside magnetopause at low and high latitudes, respectively. These reveal the typical signatures of flux transfer events (FTEs), namely bipolar perturbations in the magnetic field component normal to the local magnetopause, enhancements in the local magnetic field strength and mixing of magnetospheric and magnetosheath plasmas. Further evidence of magnetic reconnection is inferred from the ground-based signatures of pulsed ionospheric flow observed over an extended interval. In order to ascertain the location of the reconnection site responsible for the FTEs, a simple model of open flux tube motion over the surface of the magnetopause is employed. A comparison of the modelled and observed motion of open flux tubes (i.e. FTEs) and plasma flow in the magnetopause boundary layer indicates that the FTEs observed at both low and high latitudes were consistence with the existence of a tilted X-line passing through the sub-solar region, as suggested by the component reconnection paradigm. While a high latitude X-line (as predicted by the anti-parallel description of reconnection) may have been present, we find it unlikely that it could have been responsible for the FTEs observed in the pre-noon sector under the observed IMF conditions. Finally, we note that throughout the interval, the magnetosphere was bathed in ULF oscillations within the solar wind electric field. While no one-to-one correspondence with the pulsed reconnection rate suggested by the ground-based observation of pulsed ionospheric flow has been demonstrated, we note that similar periodicity oscillations were observed throughout the solar wind-magnetosphere-ionosphere system. These findings are consistent with previously proposed mechanisms of solar wind modulation of the dayside reconnection rate.
Highlights
As one of the primary mechanisms by which solar wind energy, momentum and mass enter the terrestrial magnetosphere, magnetic reconnection at the dayside magnetopause is arguably the most significant factor influencing solar wind-magnetosphere-ionosphere coupling
While magnetic reconnection is often described as occurring at locations where the magnetospheric and magnetosheath fields are aligned in an anti-parallel orientation (Dungey, 1961), it is generally accepted that reconnection will occur at some location on the magnetopause for any interplanetary magnetic field (IMF) configuration
While in the magnetosheath/boundary layer, several flux transfer events were observed by both Double Star and Cluster
Summary
As one of the primary mechanisms by which solar wind energy, momentum and mass enter the terrestrial magnetosphere, magnetic reconnection at the dayside magnetopause is arguably the most significant factor influencing solar wind-magnetosphere-ionosphere coupling. It has been proposed that magnetic reconnection can occur in the sub-solar region – the region where the magnetosheath field first comes into contact with the magnetopause – for almost any IMF orientation as long as there is a sufficiently large magnetic shear across the boundary and the IMF has a southward directed component (Gonzalez and Mozer, 1974) Such “component reconnection”, X-lines would be expected to pass through the sub-solar point and to be tilted relative to the equator. Dunlop et al, 2005; Wild et al, 2005a) These studies have concentrated on intervals of southward oriented IMF – conditions when both the anti-parallel and component reconnection descriptions of reconnection place the X-line in the vicinity of the sub-solar dayside magnetopause. Wild et al (2005b) failed to identify the likely position of the reconnection site under the prevailing duskward IMF configuration, the motivation for this re-investigation
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