Small-scale Magnetic Flux Ropes in the First two Parker Solar Probe Encounters

TL;DR

This study extends the analysis of small-scale magnetic flux ropes into the inner heliosphere using Parker Solar Probe data, revealing fewer SFRs near the Sun and highlighting the influence of turbulence and Alfvenic structures.

Contribution

First application of a Grad-Shafranov-based algorithm to identify SFRs in the inner heliosphere with PSP data, expanding understanding of their radial distribution and properties.

Findings

Fewer SFRs detected near the Sun compared to larger distances.

Magnetohydrodynamic turbulence may generate SFRs at greater distances.

Power-law relation of magnetic field strength with heliocentric distance holds down to 0.16 au.

Abstract

Small-scale magnetic flux ropes (SFRs) are a type of structures in the solar wind that possess helical magnetic field lines. In a recent report (Chen & Hu 2020), we presented the radial variations of the properties of SFR from 0.29 to 8 au using in situ measurements from the Helios, ACE/Wind, Ulysses, and Voyager spacecraft. With the launch of the Parker Solar Probe (PSP), we extend our previous investigation further into the inner heliosphere. We apply a Grad-Shafranov-based algorithm to identify SFRs during the first two PSP encounters. We find that the number of SFRs detected near the Sun is much less than that at larger radial distances, where magnetohydrodynamic (MHD) turbulence may act as the local source to produce these structures. The prevalence of Alfvenic structures significantly suppresses the detection of SFRs at closer distances. We compare the SFR event list with other event identification methods, yielding a dozen well-matched events. The cross-section maps of two selected events confirm the cylindrical magnetic flux rope configuration. The power-law relation between the SFR magnetic field and heliocentric distances seems to hold down to 0.16 au.