On the Riemann problem for the Adlam-Allen model

TL;DR

This paper analyzes the Riemann problem for the Adlam-Allen model, using theoretical and numerical methods to understand rarefaction and dispersive shock waves, and compares direct analysis with KdV reduction approximations.

Contribution

It introduces a systematic approach combining direct analysis and KdV reduction to study dispersive shock waves in the Adlam-Allen model.

Findings

Good agreement between direct analysis and numerical simulations.

KDV dispersive shock wave provides a reliable approximation.

Methodology applicable to related plasma physics problems.

Abstract

In the present work, we revisit the Adlam-Allen (AA) model in order to investigate its numerically observed rarefaction and dispersive shock waves that arise in numerical simulations of the Riemann problem associated with the model. On the one hand, we perform a direct analysis of the rarefaction and dispersive shock waves of the AA model via examining its corresponding dispersionless system and leveraging the DSW-fitting method to obtain theoretical predictions on various edge features of the dispersive shock waves. On the other hand, we review the KdV reduction of the AA model and utilize the KdV dispersive shock wave to approximate that of the AA model. Relevant numerical comparisons demonstrate the good performance of not only the direct analysis on the AA dispersive shock wave, but also of the approximation via the KdV DSW. These methodologies provide a systematic toolbox for analyzing the outcome of Riemann problems in not only this fundamental setting of cold plasmas but also potentially in related plasma-physics problems.