Investigation of Dynamics of Self-Similarly Evolving Magnetic Clouds

TL;DR

This paper investigates the evolution of self-similarly expanding magnetic clouds in the solar wind, deriving analytical solutions and validating them with numerical simulations to understand their dynamics and conserved properties.

Contribution

It introduces a self-similar analytical model for cylindrically symmetric magnetic clouds and validates it with numerical simulations, extending understanding of their evolution.

Findings

Magnetic clouds maintain self-similarity during expansion.

Analytical expressions for magnetic field, velocity, density, and pressure are derived.

Self-similar solutions effectively describe the long-term evolution of MCs.

Abstract

Magnetic clouds (MCs) are "magnetized plasma clouds" moving in the solar wind. MCs transport magnetic flux and helicity away from the Sun. These structures are not stationary but feature temporal evolution. Commonly, simplified MC models are considered. The goal of the present study is to investigate the dynamics of more general, radially expanding MCs. They are considered as cylindrically symmetric magnetic structures with low plasma {\beta}. In order to study MC`evolution the self-similar approach method and a numerical approach are used. It is shown that the forces are balanced in the considered self-similarly evolving, cylindrically symmetric magnetic structures. Explicit analytical expressions for magnetic field, plasma velocity, density and pressure within MCs are derived. These solutions are characterized by conserved values of magnetic flux and helicity. We also investigate the dynamics of self-similarly evolving MCs by means of the numerical code "Graale". In addition, their expansion in a medium with higher density and higher plasma {\beta} is studied. It is shown that the physical parameters of the MCs maintain their self-similar character throughout their evolution. Conclusions. A comparison of the different self-similar and numerical solutions allows us to conclude that the evolving MCs are quite adequately described by our self-similar solutions - they retain their self-similar, coherent nature for quite a long time and over large distances from the Sun.