Characteristics of Multi-scale Current Sheets in the Solar Wind at 1 au Associated with Magnetic Reconnection and the Case for a Heliospheric Current Sheet Avalanche

Wind spacecraft measurements are analyzed to obtain a current sheet (CS) normal width d (cs) distribution of 3374 confirmed magnetic reconnection exhausts in the ecliptic plane of the solar wind at 1 au. The d (cs) distribution displays a nearly exponential decay from a peak at d (cs) = 25 d ( i ) to a median at d (cs) = 85 d ( i ) and a 95th percentile at d (cs) = 905 d ( i ) with a maximum exhaust width at d (cs) = 8077 d ( i ). A magnetic field theta-rotation angle distribution increases linearly from a relatively few high-shear events toward a broad peak at 35 degrees < theta < 65 degrees. The azimuthal phi angles of the CS normal directions of 430 thick d (cs) >= 500 d ( i ) exhausts are consistent with a dominant Parker-spiral magnetic field and a CS normal along the ortho-Parker direction. The CS normal orientations of 370 kinetic-scale d (cs) < 25 d ( i ) exhausts are isotropic in contrast, and likely associated with Alfvenic solar wind turbulence. We propose that the alignment of exhaust normal directions from narrow d (cs) similar to 15-25 d ( i ) widths to well beyond d (cs) similar to 500 d ( i ) with an ortho-Parker azimuthal direction of a large-scale heliospheric current sheet (HCS) is a consequence of CS bifurcation and turbulence within the HCS exhaust that may trigger reconnection of the adjacent pair of bifurcated CSs. The proposed HCS-avalanche scenario suggests that the underlying large-scale parent HCS closer to the Sun evolves with heliocentric distance to fracture into many, more or less aligned, secondary CSs due to reconnection. A few wide exhaust-associated HCS-like CSs could represent a population of HCSs that failed to reconnect as frequently between the Sun and 1 au as other HCSs.

Automated summary

Wind spacecraft measurements were used to analyze magnetic reconnection exhausts in the ecliptic plane of the solar wind at 1 au. The study found an exponential decay in the distribution of current sheet widths, and a linear increase in the distribution of magnetic field rotation angles. The orientations of wide exhausts were consistent with a dominant Parker-spiral magnetic field, while narrow exhausts were isotropic. These findings suggest that CS bifurcation and turbulence play a role in aligning the exhaust directions with the large-scale heliospheric current sheet.