Control of Magnetopause Flux Rope Topology by Non-local Reconnection

Lars Mejnertsen,Jeremy P Chittenden,Jonathan P Eastwood

doi:10.3389/fspas.2021.758312

Lars Mejnertsen, Jeremy P Chittenden + Show 1 more

Open Access

https://doi.org/10.3389/fspas.2021.758312

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Abstract

Dayside magnetic reconnection between the interplanetary magnetic field and the Earth’s magnetic field is the primary mechanism enabling mass and energy entry into the magnetosphere. During favorable solar wind conditions, multiple reconnection X-lines can form on the dayside magnetopause, potentially forming flux ropes. These flux ropes move tailward, but their evolution and fate in the tail is not fully understood. Whilst flux ropes may constitute a class of flux transfer events, the extent to which they add flux to the tail depends on their topology, which can only be measured in situ by satellites providing local observations. Global simulations allow the entire magnetospheric system to be captured at an instant in time, and thus reveal the interconnection between different plasma regions and dynamics on large scales. Using the Gorgon MHD code, we analyze the formation and evolution of flux ropes on the dayside magnetopause during a simulation of a real solar wind event. With a relatively strong solar wind dynamic pressure and southward interplanetary magnetic field, the dayside region becomes very dynamic with evidence of multiple reconnection events. The resulting flux ropes transit around the flank of the magnetosphere before eventually dissipating due to non-local reconnection. This shows that non-local effects may be important in controlling the topology of flux ropes and is a complicating factor in attempts to establish the overall contribution that flux ropes make in the general circulation of magnetic flux through the magnetosphere.

Highlights

Magnetic reconnection is an important process in driving the dynamics of the Earth’s magnetosphere (e.g. Eastwood et al, 2017 and references therein)
The magnetic field lines are colored by their topology: red for solar wind, blue for closed, green for open field lines connected to the South pole and purple for open field lines connected to the North pole
As in Identification of Flux Ropes Through Field Line Tracing and Topology Mapping, magnetic field lines are colored by their topology: red for interplanetary magnetic field (IMF), blue for closed, purple for open and connected to the North pole, and green for open and connected to the South pole

Summary

Introduction

Magnetic reconnection is an important process in driving the dynamics of the Earth’s magnetosphere (e.g. Eastwood et al, 2017 and references therein). Reconnection is inherently three-dimensional and non-steady (Fu et al, 2015; Wang et al, 2020), causing the formation of Flux Transfer Events (FTEs) They are thought to transfer magnetic flux and energy into the magnetosphere when they are “open”: connected to either of the planet’s poles and to the IMF. FTEs are identified in spacecraft observations by their characteristic bipolar signature in magnetic field data, typically in the component normal to the magnetopause surface (Farrugia et al, 2016; Russell & Elphic, 1978). This signature may be indicative of rotational magnetic field structures called

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