Solar Alfvenic Pulses and Mesoscale Solar Wind

TL;DR

This study quantifies small-scale Alfvenic pulses generated by solar surface features and assesses their potential to produce switchbacks in the solar wind, providing insights into solar wind dynamics and energy transfer.

Contribution

It presents the first detailed measurement of Alfvenic pulses from solar surface features and links their energy to observed solar wind switchbacks.

Findings

Alfvenic pulses carry ~10+25 erg energy, higher than magnetic switchbacks (~10+23 erg).

Alfvenic pulses can reproduce properties of switchbacks, including filling factor above 8%.

Surface-generated Alfvenic pulses may reach the solar wind with sufficient energy to generate switchbacks.

Abstract

Large-scale solar ejections are well understood, but the extent to which small-scale solar features directly influence the solar wind remains an open question, primarily due to the challenges of tracing these small-scale ejections and their impact. Here, we measure the fine-scale motions of network bright points along a coronal hole boundary in high-resolution H-alpha images from the 1.6m Goode Solar Telescope at Big Bear Solar Observatory to quantify the agitation of open flux tubes into generating Alfvenic pulses. We combine the motion, magnetic flux, and activity duration of the flux tubes to estimate the energy content carried by individual Alfvenic pulses, which is ~10+25 erg, adequately higher than the energies ~10+23 erg estimated for the magnetic switchbacks observed by the Parker Solar Probe (PSP). This implies the possibility that the surface-generated Alfvenic pulses could reach the solar wind with sufficient energy to generate switchbacks, even though some of then are expected to be reflected back in the stratified solar atmosphere. Alfvenic pulses further reproduce for the first time other properties of switchbacks, including the filling factor above ~8% at granular and supergranular scales, which correspond best to the lower end of the mesoscale structure. This quantitative result for solar energy output in the form of Alfvenic pulses through magnetic funnels provides a crucial clue to the ongoing debate about the dynamic cycle of energy exchange between the Sun and the mesoscale solar wind that has been raised, but has not been adequately addressed, by PSP near-Sun observations.