The Apparent Layered Structure of the Heliospheric Current Sheet: Multi-Spacecraft Observations
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- Foullon, C., Lavraud, B., Wardle, N.C. et al. Sol Phys (2009) 259: 389. doi:10.1007/s11207-009-9452-4
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Multiple current sheet crossings are ubiquitous features of the solar wind associated with high-beta plasma sheets, notably during the passage of the heliospheric current sheet (HCS). As the HCS is being convected past near-Earth, we attempt to resolve spatial scales and temporal variations of the apparent layered structure of the HCS, including adjacent large scale field reversals. We use several spacecraft for good spatial and cross-scale coverage, spanning 550 RE across and 900 RE along the Sun – Earth line: STEREO, ACE and Cluster. The multi-spacecraft magnetic and plasma observations within the leading edge of the sector boundary are consistent with i) a broad multi-layered structure; ii) occasional non-planar structures and Alfvénic fluctuations; iii) various stages of transient outflowing loops formed by interchange reconnection. By comparison of the observations at each spacecraft, we obtain a synthesis of the evolution between the patterns of loops, and hence of the transient outflow evolution along the sector boundary. In particular, we present circumstantial evidence that a heat flux dropout, traditionally signalling disconnection, can arise from interchange reconnection and scattering. Moreover, the inter-spacecraft comparison eliminates ambiguities between interpretations of electron counterstreaming. Overall, the sector boundary layer remains, locally, a steady structure as it is convected in the solar wind across a radial heliospheric distance of 560 – 580 RE. However, non-planar structures on the Cluster spatial scale, as well as the variations in angular changes and transition durations on the broader scale, indicate that we are not following the evolution of single loops but more likely a bunch of loops with variable properties.