Constraining the inner boundaries of COCONUT through plasma \b{eta} and Alfv\'en speed

TL;DR

This paper improves the boundary conditions of the COCONUT solar corona model by constraining plasma ta and Alfve9n speed, leading to more physically accurate simulations during solar maxima.

Contribution

It introduces a novel method to adjust boundary conditions in the COCONUT model using plasma ta and Alfve9n speed constraints, enhancing model accuracy.

Findings

Removing inexplicable fast streams by constraining Alfve9n speed.

Maintaining magnetic topology despite boundary adjustments.

Improved modeling of solar maxima conditions.

Abstract

Space weather modelling has been gaining importance due to our increasing dependency on technology sensitive to space weather effects, such as satellite services, air traffic and power grids. Improving the reliability, accuracy and numerical performance of space weather modelling tools, including global coronal models, is essential to develop timely and accurate forecasts and to help partly mitigate the space weather threat. Global corona models, however, require accurate boundary conditions, for the formulations of which we have very limited observational data. Unsuitable boundary condition prescriptions may lead to inconsistent features in the solution flow field and spoil the code's accuracy and performance. In this paper, we develop an adjustment to the inner boundary condition of the COCONUT global corona model to better capture the dynamics over and around the regions of stronger magnetic fields by constraining the plasma \b{eta} and the Alfv\'en speed. Using data from solar observations and solar atmospheric modelling codes such as Bifrost, we find that the baseline homogeneous boundary condition formulations for pressure and density do not capture the plasma conditions physically accurately. We develop a method to adjust these prescribed pressure and density values by placing constraints on the plasma \b{eta} and the Alfv\'en speed that act as proxies. We demonstrate that we can remove inexplicable fast streams from the solution by constraining the maximum Alfv\'en speed and the minimum plasma \b{eta} on the boundary surface. We also show that the magnetic topology is not significantly affected by this treatment otherwise. The presented technique shows the potential to ease the modelling of solar maxima, especially removing inexplicable features while, at the same time, not significantly affecting the magnetic field topology around the affected regions.