2010 August 1-2 sympathetic eruptions: II. Magnetic topology of the MHD background field

TL;DR

This study compares potential field source surface and MHD models to analyze the coronal magnetic topology during CMEs, revealing differences in coronal hole structures and identifying complex null line configurations affecting solar phenomena.

Contribution

It introduces a detailed MHD-based analysis of coronal magnetic topology, highlighting differences from PFSS models and identifying new structures like multiple-null separators and plasmoids.

Findings

MHD models show different coronal hole sizes and shapes compared to PFSS.

The helmet-streamer cusp line is unstable in MHD models and does not form.

Identification of three-dimensional plasmoids related to streamer blobs.

Abstract

Using a potential field source surface (PFSS) model, we recently analyzed the global topology of the background coronal magnetic field for a sequence of coronal mass ejections (CMEs) that occurred on 2010 August 1-2. Here we repeat this analysis for the background field reproduced by a magnetohydrodynamic (MHD) model that incorporates plasma thermodynamics. As for the PFSS model, we find that all three CME source regions contain a coronal hole that is separated from neighboring coronal holes by topologically very similar pseudo-streamer structures. However, the two models yield very different results for the size, shape, and flux of the coronal holes. We find that the helmet-streamer cusp line, which corresponds to a source-surface null line in the PFSS model, is structurally unstable and does not form in the MHD model. Our analysis indicates that generally, in MHD configurations, this line rather consists of a multiple-null separator passing along the edge of disconnected flux regions. Some of these regions are transient and may be the origin of so-called streamer blobs. We show that the core topological structure of such blobs is a three-dimensional "plasmoid", consisting of two conjoined flux ropes of opposite handedness, which connect at a spiral null point of the magnetic field. Our analysis reveals that such plasmoids appear also in pseudo-streamers on much smaller scales. These new insights into the coronal magnetic topology provide some intriguing implications for solar energetic particle events and for the properties of the slow solar wind.