The preferential orientation of magnetic switchbacks, implications for solar magnetic flux transport

TL;DR

This study analyzes the orientation of magnetic switchbacks in the solar wind using Parker Solar Probe data, revealing a systematic preferential clockwise orientation and a consistent deflection pattern, which informs theories of switchback formation.

Contribution

It introduces a statistical model fitting switchback deflections as a distinct population, demonstrating a preferential orientation and providing insights into their formation mechanisms.

Findings

Switchbacks show a systematic clockwise bias in deflections.

The accuracy of the Parker spiral model varies with distance from the Sun.

A 12-hour patch of aligned switchbacks exhibits consistent deflection directions.

Abstract

We investigate the orientation of the magnetic field deflections in switchbacks (SB) to determine if they are characterised by a possible preferential orientation. We compute the deflection angles of the magnetic field relative to the Parker spiral direction for encounters 1 to 9 of the PSP mission. We first characterize the distribution of these deflection angles for calm solar wind intervals, and assess the precision of the Parker model as a function of distance to the Sun. We then assume that the solar wind is composed of two populations, the background calm solar wind and the population of SB, characterized by larger fluctuations. We model the total distribution of deflection angles we observe in the solar wind as a weighed sum of two distinct normal distributions, each corresponding to one of the populations. We fit the observed data with our model using a MCMC algorithm and retrieve the most probable mean vector and covariance matrix coefficients of the two Gaussian functions, as well as the population proportion. We first observe that the accuracy of the spiral direction in the ecliptic is a function of radial distance, in a manner that is consistent with PSP being near the solar wind acceleration region. We then find that the fitted switchback population presents a systematic bias in its deflections compared to the calm solar wind population. This result holds for all encounters but E6, and regardless of the magnetic field main polarity. This implies a marked preferential orientation of SB in the clockwise direction in the ecliptic plane, and we discuss this result and its implications in the context of the existing switchback formation theories. Finally, we report the observation of a 12-hour patch of SB that systematically deflect in the same direction, so that the magnetic field vector tip within the patch deflects and returns to the Parker spiral within a given plane.