Characteristics of Multi-Scale Current Sheets in the Solar Wind at 1 AU Associated with Magnetic Reconnection

Abstract: The solar wind is a turbulent plasma regime that supports current sheets of many spatial scales. The vast majority of current sheets are narrower than 400 km. We associate these kinetic-scale current sheets with solar wind turbulence at 1 AU. The largest current sheet is 64,000 km wide on average, or 150 times wider than the more prevalent and turbulent ones. This is the well-known Heliospheric Current Sheet (HCS) that typically resides in the vicinity of Sector Boundary crossings of the Heliospheric Magnetic Field (HMF). Current sheets are known to tear due to a magnetic reconnection process when they are sufficiently thin. Here, we present a large study of reconnection-associated current sheets from the Wind spacecraft at 1 AU. Current sheets from very big scales (≥500 di) and down to very small scales (~25 di) are shown to be aligned with a dominant Parker-spiral HMF orientation, where 1 di~100 km at 1 AU. The orientations of kinetic-scale (<25 di) events are isotropic in contrast, suggesting a source in solar wind turbulence. We propose that the association of reconnecting current sheets with the Parker HMF from ~25 di to well beyond 500 di is a consequence of a multi-scale current sheet bifurcation process that breaks apart large current sheets into successively smaller ones in a cascade-like process. In one example, a large-scale 784 di event was bifurcated in two ~22 di current sheets with a scaling factor of 35. This intriguing result directly addresses the often “tattered” character of the HCS at 1 AU, and the observation [Smith, 2001] that “sector plots end up with a large number of ambiguous or uncertain identifications”.