# Heliospheric Evolution of Magnetic Clouds

## TL;DR

This study analyzes the interplanetary evolution of magnetic clouds using spacecraft data, revealing complex expansion behaviors, deviations from self-similar models, and the influence of magnetic reconnection and deformation processes.

## Contribution

It provides a detailed statistical and individual analysis of magnetic cloud expansion, highlighting deviations from ideal models and the roles of reconnection and deformation.

## Key findings

- Most magnetic clouds do not follow self-similar expansion.
- Magnetic field decreases slower than expected in most cases.
- Magnetic reconnection and deformation significantly affect cloud evolution.

## Abstract

Interplanetary evolution of eleven magnetic clouds (MCs) recorded by at least two radially aligned spacecraft is studied. The in situ magnetic field measurements are fitted to a cylindrically symmetric Gold-Hoyle force-free uniform-twist flux-rope configuration. The analysis reveals that in a statistical sense the expansion of studied MCs is compatible with self-similar behavior. However, individual events expose a large scatter of expansion rates, ranging from very weak to very strong expansion. Individually, only four events show an expansion rate compatible with the isotropic self-similar expansion. The results indicate that the expansion has to be much stronger when MCs are still close to the Sun than in the studied 0.47 - 4.8 AU distance range. The evolution of the magnetic field strength shows a large deviation from the behavior expected for the case of an isotropic self-similar expansion. In the statistical sense, as well as in most of the individual events, the inferred magnetic field decreases much slower than expected. Only three events show a behavior compatible with a self-similar expansion. There is also a discrepancy between the magnetic field decrease and the increase of the MC size, indicating that magnetic reconnection and geometrical deformations play a significant role in the MC evolution. About half of the events show a decay of the electric current as expected for the self-similar expansion. Statistically, the inferred axial magnetic flux is broadly consistent with it remaining constant. However, events characterized by large magnetic flux show a clear tendency of decreasing flux.