Evaluation of electromotive force in interplanetary space

Yasuhito Narita,Zoltán Vörös

doi:10.5194/angeo-36-101-2018

Yasuhito Narita, Zoltán Vörös

Open Access

https://doi.org/10.5194/angeo-36-101-2018

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Abstract

Abstract. Electromotive force plays a central role in the turbulent dynamo mechanism and carries important information on the nature of the turbulent fields. In this study, an analysis method is developed for the electromotive force and the transport coefficients such as those for the α effect (coefficient α) and the turbulent diffusivity (coefficient β). The method is applied to a magnetic cloud event observed by the Helios 2 spacecraft in the inner heliosphere. The electromotive force is enhanced together with the magnetic cloud event by 1 or 2 orders of magnitude, suggesting that the magnetic field can locally be amplified in the heliosphere, presumably for a short time.

Highlights

The essential part in the dynamo mechanism amplifying the large-scale magnetic field lies in the existence of electromotive force
Electromotive force plays a central role in the turbulent dynamo mechanism and carries important information on the nature of the turbulent fields
In the mean-field dynamo theory, the electromotive force is assumed to be linear in the mean magnetic field B0 to the first order, and in the spatial gradient of the mean field such as the curl of the mean magnetic field, ∇ ×B0, and the curl of the mean flow velocity, ∇ × U 0

Summary

Introduction

The essential part in the dynamo mechanism amplifying the large-scale magnetic field lies in the existence of electromotive force. The second term with the coefficient β (which has the same dimension as that of the magnetic diffusivity) and the curl of the mean magnetic field (which is proportional to the electric current density for the mean magnetic field) is the turbulent magnetic diffusion, and the third term with the coefficient γ and the curl of the large-scale flow velocity the cross helicity dynamo. It is important to note that the electromotive force is a second-order fluctuation quantity and is in the same class as the energy densities of the fluctuating fields (for the magnetic field and the flow velocity) and the helicity densities (magnetic helicity, kinetic helicity, and cross helicity). This paper is motivated by a wish to fill the gap in the application of the electromotive force between laboratory and space plasma studies

Estimates of transport coefficients

Magnetic cloud in interplanetary space

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