Electric Currents in Geospace and Beyond

Andreas Keiling, Octav Marghitu, Michael Wheatland, Andreas Keiling, Octav Marghitu, Michael Wheatland

• Publisher: American Geophysical Union
• Year: 2018
• Print ISBN: 9781119324492
• eBook ISBN: 9781119325789
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Biology
• Index: Biological Sciences

Electric currents are fundamental to the structure and dynamics of space plasmas, including our own near-Earth space environment, or "geospace."This volume takes an integrated approach to the subject of electric currents by incorporating their phenomenology and physics for many regions in one volume. It covers a broad range of topics from the pioneers of electric currents in outer space, to measurement and analysis techniques, and the many types of electric currents.

• First volume on electric currents in space in over a decade that provides authoritative up-to-date insight on the current status of research
• Reviews recent advances in observations, simulation, and theory of electric currents
• Provides comparative overviews of electric currents in the space environments of different astronomical bodies

Electric Currents in Geospace and Beyond serves as an excellent reference volume for a broad community of space scientists, astronomers, and astrophysicists who are studying space plasmas in the solar system. Read an interview with the editors to find out more:
https://eos.org/editors-vox/electric-currents-in-outer-space-run-the-show

Part I: Introduction

1
Pioneers of Electric Currents in Geospace

Asgeir Brekke

UiT Norges Arktiske Universitet, Department of Physics and Technology, Tromso, Norway

ABSTRACT

This review shows that the progress of our understanding of the electric currents in geospace has gone through a progressive development from the time of the Enlightenment in the early eighteenth century to the Space Age in the 1970s. When it was found that magnetic field variations were caused by electric currents in the upper atmosphere, important steps were made in the late part of the nineteenth century. The aurora borealis was believed to be an electric phenomenon by several authors as early as the 1750s. The current system linking the creation of the aurora became a main field of interest in the beginning of the twentieth century and has remained so until our time. At present, we have a large variety of instruments and methods such as satellite and ground‐based experiments of different kinds and capacities as well as dedicated computer models to study these current systems further. What appears to be lacking, however, is a more detailed knowledge of the variation of the ionospheric conductivities in space and time.

1.1. INTRODUCTION

Geospace is often used as a denotation of the space between the Sun and the Earth. Solar wind plasma is streaming through geospace and due to the omnipresent magnetic field, electrons and positive ions blowing with the wind are forced to move in different directions with electric currents as an outcome. These electric currents forming in the magnetosphere are connected to the ionosphere of the Earth by field‐aligned currents that are closed by horizontal currents in the upper atmosphere. The effects on ground caused by these currents have been a challenge for humankind for generations. This chapter will give an overview of the development of our understanding of these electric currents in geospace from the time of the Enlightenment until the 1970s. Important milestones reached in the eighteenth century like the understanding of the relationship between the occurrence of aurora borealis and magnetic field fluctuations, as well as the fact that the aurora is an electrical phenomenon, are elucidated. The important recognition in the last part of the nineteenth century of diurnal magnetic field fluctuations being a result of electric currents in the atmosphere is emphasized. The introduction of cathode rays and electrically charged particles from the Sun being the cause of the aurora, field‐aligned currents, and magnetic storms are given a broad coverage including experimental mapping and models of the current systems involved.

It is expected that the multidimensional European Incoherent Scatter Radar EISCAT_3D system in Scandinavia together with modern space‐borne technology will improve our ability to better understand the cause and connections of the electric currents in geospace.

1.2. AURORA BOREALIS AND VARIATIONS IN THE EARTH'S MAGNETIC FIELD

We are all standing on the shoulders of somebody. When we are tracing the pioneers of our field, we have to make a choice where to start. Chapman and Bartles [1940] claimed that Sir Edmund Halley was the first to publish an observed connection between the aurora borealis and magnetic storms in London on 17 March 1716. From these observations, Halley concluded that the position as well as the shape of the aurora was strongly controlled by the magnetic field. Furthermore, Halley presented the idea that the aurora was due to a magnetic effluvia that streamed out from pores in the Earth's surface and by following the magnetic field lines reached far away from the surface of the Earth, where the ether became luminous [Halley, 1716]. Although Halley did not relate his observations to electricity, it might be natural to start this review by mentioning his contributions to the field as they lifted the understanding of the auroral phenomenon from speculative ideas to a frame of reference based on natural science. Furthermore, the aurora borealis is a reasonable introduction to the field as its striking appearance has inspired many scientists throughout history to relate it to electric currents in geospace.

It has been said that the watchmaker George Graham (1673–1751) in London was the first to observe a relationship between the aurora borealis and the variations in the magnetic needle in 1722 [Chapman and Bartels, 1940]. In his paper, however, Graham reported peculiar variations in the direction of a magnetic needle. As he described his experiment and dismissed any possible artificial disturbances in his instrument that could explain the remarkable observations, he wrote:

“I am well assured these Changes in the Direction are owing to some other Cause than Friction of the Needle upon the Pin; but what that Cause is I cannot say, for it seems to depend neither upon Heat nor Cold, a dry or moist Air, clear or cloudy, windy or calm Weather, nor the Height of the Barometer” [Graham, 1724–1725, 96–107].

Clearly there was an outside cause of the variations, and in hindsight it is tempting to assume that it must have been at a time of occurrence of northern lights.

Later on, however, the Swedish astronomer and physicist Anders Celsius (1701–1744) probably became the first to have realized a relationship between the aurora borealis and variations in the position of the magnetic needle as he encouraged Olav Peter Hiorter (1696–1750) to look for a possible connection between the occurrence of these two phenomena. Hiorter meticulously made 6638 readings of the position of the magnetic needle from 19 January 17...

Table of contents

• Cover
• Title Page
• Table of Contents
• CONTRIBUTORS
• PREFACE
• Part I:: Introduction
• Part II:: Ring Currents
• Part III:: Current Sheets
• Part IV:: Field‐Aligned Currents
• Part V:: Ionospheric Currents
• Part VI:: Other Current Systems
• INDEX
• End User License Agreement