[Paper Review] Threaded-Field-Lines Model for the Low Solar Corona Powered by the Alfven Wave Turbulence

И. В. Соколов, B. van der Holst+7 more|arXiv (Cornell University)|Sep 8, 2016

Solar and Space Plasma Dynamics40 references3 citations

TL;DR

This paper presents the Threaded-Field-Line Model (TFLM) coupled with the Alfvén Wave Turbulence-based AWSoM-R model to simulate the low solar corona and transition region with high computational efficiency. By tracing magnetic field lines from a boundary at 1.1 R⊙ and solving 1D plasma and wave equations along each line, the model achieves faster-than-real-time performance on ~200 cores while accurately reproducing observed coronal heating, solar wind acceleration, and intermittent slow wind structures like streamer blobs.

ABSTRACT

We present an updated global model of the solar corona, including the transition region. We simulate the realistic tree-dimensional (3D) magnetic field using the data from the photospheric magnetic field measurements and assume the magnetohydrodynamic (MHD) Alfvén wave turbulence and its non-linear dissipation to be the only source for heating the coronal plasma and driving the solar wind. In closed field regions the dissipation efficiency in a balanced turbulence is enhanced. In the coronal holes we account for a reflection of the outward propagating waves, which is accompanied by generation of weaker counter-propagating waves. The non-linear cascade rate degrades in strongly imbalanced turbulence, thus resulting in colder coronal holes. The distinctive feature of the presented model is the description of the low corona as almost-steady-state low-beta plasma motion and heat flux transfer along the magnetic field lines. We trace the magnetic field lines through each grid point of the lower boundary of the global corona model, chosen at some heliocentric distance, $R=R_{b}\sim1.1\ R_\odot$ well above the transition region. One can readily solve the plasma parameters along the magnetic field line from 1D equations for the plasma motion and heat transport together with the Alfvén wave propagation, which adequately describe physics within the heliocentric distances range, $R_{\odot}

Motivation & Objective

• To develop a computationally efficient, physics-based model of the low solar corona and transition region driven solely by Alfvén wave turbulence.
• To eliminate ad hoc heating functions and free parameters by relying on nonlinear wave dissipation as the sole energy source for coronal heating and solar wind acceleration.
• To reproduce observed bimodal solar wind structure—hot, bright open field regions and cold, dark coronal holes—through wave reflection and turbulence imbalance.
• To achieve faster-than-real-time simulation performance on ~200 cores while maintaining high accuracy in plasma and magnetic field structure.

Proposed method

• The model uses 3D photospheric magnetic field data as input to reconstruct the global coronal magnetic field.
• Magnetic field lines are traced from a lower boundary at Rb = 1.1 R⊙ to compute 1D plasma and wave dynamics along each field line.
• The 1D equations include momentum, energy, and wave amplitude evolution with Alfvén wave turbulence dissipation as the primary heating mechanism.
• In closed-field regions, balanced turbulence leads to efficient dissipation and heating; in coronal holes, wave reflection generates weak counter-propagating waves, reducing dissipation and cooling the plasma.
• The TFLM is interfaced with the full 3D MHD AWSoM-R model at Rb to enable global, steady-state solutions with high fidelity.
• Time-dependent simulations are performed to capture dynamic phenomena such as streamer blob formation, even with steady-state boundary conditions.

Experimental results

Research questions

• RQ1 Can Alfvén wave turbulence alone explain the observed temperature and density structure of the low solar corona and transition region?
• RQ2 How does wave reflection in coronal holes affect turbulence imbalance and heating efficiency, leading to colder plasma compared to open field regions?
• RQ3 Can a threaded-field-line approach enable faster-than-real-time simulation of the solar corona and inner heliosphere without sacrificing physical accuracy?
• RQ4 What role does wave turbulence nonlinearity play in the intermittent detachment of plasma blobs from helmet streamers?
• RQ5 How well does the model reproduce observed solar wind speed distributions and latitudinal variations, particularly during solar minimum?

Key findings

• The model successfully reproduces the bimodal solar wind structure: hot, bright closed-field regions and cold, dark coronal holes, due to turbulence imbalance from wave reflection.
• Intense wave reflection in active regions enhances wave dissipation, explaining the enhanced brightness of active regions in EUV and X-ray observations.
• The model captures intermittent streamer blob formation with a periodicity of ~40 hours, consistent with observations from the Ulysses mission.
• The radial velocity distribution in the model matches Ulysses SWOOPS observations across all latitudes, including the slow wind at low latitudes and fast wind at high latitudes.
• The simulation achieves faster-than-real-time performance on ~200 cores by decoupling 1D field-line solutions from the global 3D MHD framework.
• Time-dependent simulations reveal dynamic helmet streamer evolution and pressure-driven disconnection events, even with steady-state magnetic boundary conditions.