Global Coronal Equilibria with Solar Wind Outflow

TL;DR

This paper introduces an improved magnetic field model for the solar corona that incorporates solar wind outflow, providing more accurate initial conditions for simulations and better agreement with observations.

Contribution

It presents a magneto-frictional equilibrium model with solar wind outflow, avoiding artificial source surfaces and improving coronal magnetic field approximations.

Findings

Outflow fields better match real coronal magnetic fields.

The model increases open magnetic flux, aligning with in situ data.

Open-source Python implementation provided.

Abstract

Given a known radial magnetic field distribution on the Sun's photospheric surface, there exist well-established methods for computing a potential magnetic field in the corona above. Such potential fields are routinely used as input to solar wind models, and to initialize magneto-frictional or full magnetohydrodynamic simulations of the coronal and heliospheric magnetic fields. We describe an improved magnetic field model which calculates a magneto-frictional equilibrium with an imposed solar wind profile (which can be Parker's solar wind solution, or any reasonable equivalent). These `outflow fields' appear to approximate the real coronal magnetic field more closely than a potential field, take a similar time to compute, and avoid the need to impose an artificial source surface. Thus they provide a practical alternative to the potential field model for initializing time-evolving simulations or modeling the heliospheric magnetic field. We give an open-source Python implementation in spherical coordinates and apply the model to data from Solar Cycle 24. The outflow tends to increase the open magnetic flux compared to the potential field model, reducing the well known discrepancy with in situ observations.