Subproton-scale Intermittency in Near-Sun Solar Wind Turbulence Observed by the Parker Solar Probe

High time-resolution solar wind magnetic field data are employed to study statistics describing intermittency near the first perihelion (similar to 35.6 R) of the Parker Solar Probe mission. A merged data set employing two instruments on the FIELDS suite enables broadband estimation of higher-order moments of magnetic field increments, with five orders established with reliable accuracy. The duration, cadence, and low noise level of the data permit evaluation of scale dependence of the observed intermittency from the inertial range to deep subproton scales. The results support multifractal scaling in the inertial range, and monofractal but non-Gaussian scaling in the subproton range, thus clarifying suggestions based on data near Earth that had remained ambiguous due to possible interference of the terrestrial foreshock. The physics of the transition to monofractality remains unclear but we suggest that it is due to a scale-invariant population of current sheets between ion and electron inertial scales; the previous suggestion of incoherent kinetic-scale wave activity is disfavored as it presumably leads re-Gaussianization that is not observed.

Automated summary

This study used high time-resolution solar wind magnetic field data from the Parker Solar Probe mission to analyze intermittency statistics near the first perihelion. The results revealed multifractal scaling in the inertial range, and monofractal but non-Gaussian scaling in the subproton range, with the transition to monofractality attributed to the presence of scale-invariant current sheets between ion and electron inertial scales. The study also ruled out incoherent kinetic-scale wave activity as a factor in the transition.