Solar Spicules, Filigrees and Solar Wind Switchbacks

TL;DR

This study suggests that solar spicules, originating from filigrees in unipolar magnetic regions, are likely sources of solar wind switchbacks, supported by high-resolution observations and their spatial-temporal properties.

Contribution

It identifies spicules as a unique candidate for solar wind switchbacks, highlighting their origin, clustering, and occurrence rate, which differ from other solar phenomena like coronal jets.

Findings

Spicules originate from filigrees in unipolar regions.

Spicule clustering and timing match switchback properties.

High occurrence rate of spicules supports their role in solar wind dynamics.

Abstract

Spicules, the smallest observable jet-like dynamic features ubiquitous in the chromosphere, are supposedly an important potential source for small-scale solar wind transients, with supporting evidence yet needed. We studied the high-resolution H-alpha images (0.10'') and magnetograms (0.29'') from Big Bear Solar Observatory (BBSO) to find that spicules are an ideal candidate for the solar wind magnetic switchbacks detected by the Parker Solar Probe (PSP). It is not that spicules are a miniature of coronal jets, but that they have unique properties not found in other solar candidates in explaining solar origin of switchbacks. (1) The spicules under this study originate from filigrees, all in a single magnetic polarity. Since filigrees are known as footpoints of open fields, the spicule guiding field lines can form a unipolar funnel, which is needed to create an SB patch, a group of fieldlines that switch from one common base polarity to the other polarity. (2) The spicules come in a cluster lined up along a supergranulation boundary, and the simulated waiting times from their spatial intervals exhibit a number distribution continuously decreasing from a few sec to ~30 min, similar to that of switchbacks. (3) From a time-distance map for spicules, we estimate their occurrence rate as 0.55 spicules per Mm^2 and second, sufficiently high for detection by PSP. In addition the dissimilarity of spicules with coronal jets, including the absence of base brightening and low correlation with EUV emission is briefly discussed.