Characteristics of the flankmagnetopause: Cluster observations

TL;DR

This study analyzes the properties of the flank magnetopause using Cluster satellite data, revealing its greater thickness, dawn-dusk asymmetry, and complex multi-sheet current structure, which differ from the classic thin current sheet model.

Contribution

It provides detailed measurements of flank magnetopause thickness, asymmetry, and current profiles, highlighting its complex multi-sheet structure and challenging existing simplified models.

Findings

Flank magnetopause is thicker than dayside.

Dawn-dusk asymmetry in thickness and current density.

Magnetopause often consists of multiple current sheets.

Abstract

The magnetopause is a current sheet forming the boundary between the geomagnetic field on one side and the shocked solar wind on the other side. This paper discusses properties of the low-latitude dawn and dusk flanks of the magnetopause. The reported results are based on a large number of measurements obtained by the Cluster satellites during magnetopause traversals. Using a combination of single-spacecraft and multispacecraft techniques, we calculated macroscopic features such as thickness, location, and motion of the magnetopause. The results show that the typical flank magnetopause is significantly thicker than the dayside magnetopause and also possesses a pronounced and persistent dawn-dusk asymmetry. Thicknesses vary from 150 to 5000 km, with an median thickness of around 1400 km at dawn and around 1150 km at dusk. Current densities are on average higher on dusk, suggesting that the total current at dawn and dusk are similar. Solar wind conditions and the interplanetary magnetic field cannot fully explain the observed dawn-dusk asymmetry. For a number of crossings we were also able to derive detailed current density profiles. The profiles show that the magnetopause often consists of two or more adjacent current sheets, each current sheet typically several ion gyroradii thick and often with different current direction. This demonstrates that the flank magnetopause has a structure that is more complex than the thin, one-dimensional current sheet described by a Chapman-Ferraro layer.