Clustering of Intermittent Magnetic and Flow Structures near Parker Solar Probe's First Perihelion -- A Partial-Variance-of-Increments Analysis

TL;DR

This study analyzes intermittent magnetic and flow structures near the Sun using PVI technique on Parker Solar Probe data, revealing clustering and random processes in solar wind turbulence at close solar distances.

Contribution

It applies the PVI method to PSP data to characterize the statistical nature of intermittent structures, highlighting clustering and Poisson-like behavior in solar wind turbulence.

Findings

Power-law waiting time distributions for short intervals indicating clustering.

Exponential waiting times for longer intervals suggesting a Poisson process.

Results are consistent with turbulence observations near Earth.

Abstract

During the Parker Solar Probe's (PSP) first perihelion pass, the spacecraft reached within a heliocentric distance of \(\sim 37~R_\odot\) and observed numerous magnetic and flow structures characterized by sharp gradients. To better understand these intermittent structures in the young solar wind, an important property to examine is their degree of correlation in time and space. To this end, we use the well-tested Partial Variance of Increments (PVI) technique to identify intermittent events in FIELDS and SWEAP observations of magnetic and proton-velocity fields (respectively) during PSP's first solar encounter, when the spacecraft was within 0.25 au from the Sun. We then examine distributions of waiting times between events with varying separation and PVI thresholds. We find power-law distributions for waiting times shorter than a characteristic scale comparable to the correlation time, suggesting a high degree of correlation that may originate in a clustering process. Waiting times longer than this characteristic time are better described by an exponential, suggesting a random memory-less Poisson process at play. These findings are consistent with near-Earth observations of solar wind turbulence. The present study complements the one by Dudok de Wit et al. (2020, present volume), which focuses on waiting times between observed "switchbacks" in the radial magnetic field.