The Solar Corona as probed by Comet Lovejoy (C/2011 W3)

TL;DR

This study uses EUV images of Comet Lovejoy to reveal detailed magnetic and density structures in the solar corona, highlighting their impact on wave propagation and solar wind models.

Contribution

It provides new observational evidence of coronal density contrasts and magnetic field structures using cometary emissions, and compares these with MHD models and pickup ion theory.

Findings

Coronal density contrasts of at least a factor of 6 between flux tubes.

Magnetic field structures influence cometary emission movement and broadening.

Variations in Alfven speed affect wave propagation and solar wind acceleration.

Abstract

EUV images of Comet Lovejoy (C/2011 W3) from the AIA show striations related to the magnetic field structure in both open and closed magnetic regions. The brightness contrast implies coronal density contrasts of at least a factor of 6 between neighboring flux tubes over scales of a few thousand km. These density structures imply variations in the Alfven speed on a similar scale. They will drastically affect the propagation and dissipation of Alfven waves, and that should be taken into account in models of coronal heating and solar wind acceleration. In each striation, the cometary emission moves along the magnetic field and broadens with time. The speed and the rate of broadening are related to the parallel and perpendicular components of the velocities of the cometary neutrals when they become ionized. We use an MHD model of the coronal magnetic field and the theory of pickup ions to compare the measurements with theoretical predictions, in particular with the energy lost to Alfven waves as the cometary ions isotropize.