Magnetic Field Intermittency Statistics in the Expanding Solar Wind: Parker Solar Probe (Encounters 1-3), Helios 1 (0.3 to 1AU), and Voyager 1 (1 to 10AU)

Abstract:

We perform statistics on magnetic field vector components for Parker Solar Probe, Helios 1, and Voyager 1 spacecraft to explore how intermittency evolves from the inner-heliosphere out to 10AU. Partial Variance of Increments (PVI) and its Probability Density Function (PDF), Second Order Structure Function (SF2), Auto-correlation, and Scale Dependent Kurtosis (SDK) are used to measure intermittency at different heliocentric distances. The Goddard Space Flight Center Space Physics Data Facility (GSFCSPDF) provides magnetic field measurements for Parker Solar Probe at 6.8 millisecond cadence, Helios 1 at 6 second cadence, and Voyager 1 at 1.92 second cadence. We check the SF2 to determine the inertial range and examine SDKs to investigate intermittency of certain regions in terms of the­­ir Gaussianity. Auto-correlations are used to retrieve correlation lengths and the PDF of PVIs suggests that there is a lower probability of finding strong magnetic fluctuations at greater heliocentric distance. We observe that lower effective Reynolds number intervals yield more Gaussian-like statistics, i.e., lower SDK. Perhaps counter-intuitively, decreasing effective Reynolds Number (Re) is found as heliocentric distance increases. Furthermore, we explore the relationship between SDK, either held at a fixed multiple of the ion inertial length or a constant fraction of the correlation length, and Re, which also suggests finding weaker intermittency in lower Re regions. We also note that a refined Voyager 1 magnetic field dataset is used and will be made available through the GSFCSPDF. The Helios 1 and Voyager 1 results are fully consistent in these conclusions and can provide predictions for Solar Orbiter and Parker Solar Probe observations. This research is supported in part by NASA HelioGI grant 80NSSC19K0284 and HelioSR grant and NNXNNX17AB79G.