Time-Dependent Tomographic Reconstruction of the Solar Corona

TL;DR

This paper introduces a novel time-dependent tomographic reconstruction method for the solar corona that accounts for its temporal variations, improving accuracy over traditional static approaches using regularization and synthetic modeling.

Contribution

It develops a spatio-temporal regularization technique and a co-rotating regularization, validated with a synthetic MHD model, enabling dynamic 3D electron density reconstructions from LASCO-C2 images.

Findings

Successfully reproduces a time-varying MHD corona model

Applies the method to 53 LASCO-C2 images from March 2009

Paves the way for 20-year time-dependent coronal reconstructions

Abstract

Solar rotational tomography (SRT) applied to white-light coronal images observed at multiple aspect angles has been the preferred approach for determining the three-dimensional (3D) electron density structure of the solar corona. However, it is seriously hampered by the restrictive assumption that the corona is time-invariant which introduces significant errors in the reconstruction. We first explore several methods to mitigate the temporal variation of the corona by decoupling the "fast-varying" inner corona from the "slow-moving" outer corona using multiple masking (either by juxtaposition or recursive combination) and radial weighting. Weighting with a radial exponential profile provides some improvement over a classical reconstruction but only beyond 3 Rsun. We next consider a full time-dependent tomographic reconstruction involving spatio-temporal regularization and further introduce a co-rotating regularization aimed at preventing concentration of reconstructed density in the plane of the sky. Crucial to testing our procedure and properly tuning the regularization parameters is the introduction of a time-dependent MHD model of the corona based on observed magnetograms to build a time-series of synthetic images of the corona. Our procedure, which successfully reproduces the time-varying model corona, is finally applied to a set of of 53 LASCO-C2 pB images roughly evenly spaced in time from 15 to 29 March 2009. Our procedure paves the way to a time-dependent tomographic reconstruction of the coronal electron density to the whole set of LASCO-C2 images presently spanning 20 years.