Coronal Bright Points as Possible Sources of Density Variations in the Solar Corona

Léa Griton,Nicolas Poirier,Athanasios Kouloumvakos,Rui F Pinto,Michäel Lavarra,Alexis P Rouillard

doi:10.3847/1538-4357/ab7b76

Abstract

Abstract Recent analysis of high-cadence white-light images taken by the Solar-Terrestrial RElations Observatory near solar maximum has revealed that outflowing density structures are released in a ubiquitous manner in the solar wind. The present study investigates whether these density fluctuations could originate from the transient heating of the low corona observed during coronal bright points (CBPs). We assume that part of the intense heating measured during CBPs occurs at the coronal base of open magnetic fields that channel the forming solar wind. We employ the solar wind model MULTI-VP to quantify the plasma compression induced by transient heating and investigate how the induced perturbation propagates to the upper corona. We show that for heating rates with statistics comparable to those observed during CBPs, the compressive wave initially increases the local plasma density by a factor of up to 50% at 5 R ⊙. The wave expands rapidly beyond 30 solar radii and the local enhancement in density decreases beyond. Based on the occurrence rates of CBPs measured in previous studies, we impose transient heating events at the base of thousands of open magnetic field lines to study the response of the entire 3D corona. The simulated density cubes are then converted into synthetic white-light imagery. We show that the resulting brightness variations occupy all position angles in the images on timescales of hours. We conclude that a significant part of the ubiquitous brightness variability of the solar corona could originate in the strong transient heating of flux tubes induced by CBPs.

Highlights

The past two decades of coronal observations have revealed the highly variable nature of the solar corona on all measurable spatial and temporal scales from the deep layers of the solar atmosphere to the upper corona
In order to do so, we ran a series of solar wind simulations that take into account the specific magnetic topology of the corona of the DeForest et al (2018) deep-field campaign, to which we introduce perturbations that mimic localized heating events caused by coronal bright points (CBPs)
Heating perturbations occurring in the low corona should be expected to be triggered in a much more random manner than in the simulations we described in the previous section

Summary

Introduction

The past two decades of coronal observations have revealed the highly variable nature of the solar corona on all measurable spatial and temporal scales from the deep layers of the solar atmosphere to the upper corona. The largest structures observed by DeForest et al (2018) were related in the study to streamer blobs released in the slow solar wind from the tips of streamers (Sheeley et al 1997).

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Conclusion