The solar-terrestrial environment

The solar-terrestrial environment

(Parte 1 de 6)

This textbook describes physical conditions in the upper atmosphere and magnetosphere of the Earth. This geospace environment begins 70 kilometres above the surface of the Earth and extends in near space to many times the Earth's radius. It is the region of near-Earth environment where the Space Shuttle flies, the aurora is generated, and the outer atmosphere meets particles streaming out of the sun. The account is introductory, at a level suitable for readers with a basic background in engineering or physics. The intent is to present basic concepts, and for that reason the mathematical treatment is not complex. SI units are given throughout, with helpful notes on units where these are likely to be encountered in the research literature. Each chapter has a reading list also.

There are three introductory chapters that give basic physics and explain the principles of physical investigation. The principal material contained in the main part of the book covers the neutral and ionized upper atmosphere, the magnetosphere, and structures, dynamics, disturbances and irregularities. The concluding chapter deals with technological applications.

This textbook is suitable for advanced undergraduate and new postgraduate students who are taking introductory courses in upper atmospheric, ionospheric, or magnetospheric physics. It is a successor to The Upper Atmosphere and Solar-Terrestrial Relations by J. K. Hargreaves, first published in 1979.

Cambridge atmospheric and space science series The solar-terrestrial environment

Cambridge atmospheric and space science series

Editor s

Alexander J. Dessler John T. Houghton Michael J. Rycroft

Titles in print in this series

M. H. Rees, Physics and chemistry of the upper atmosphere

Roger Daley, Atmospheric data analysis

Ya. L. Al'pert, Space plasma, Volumes 1 and 2 J. R. Garratt, The atmospheric boundary layer

J. K. Hargreaves, The solar-terrestrial environment Sergei Sazhin, Whistler-mode waves in a hot plasma

S. Peter Gary, Theory of space plasma microinstabilities Ian N. James, Introduction to circulating atmospheres

Tamas I. Gombosi, Gaskinetic theory

Martin Walt, Introduction to geomagnetically trapped radiation B. A. Kagan, Ocean-atmosphere interaction and climate modelling

The solar-terrestrial environment

An introduction to geospace - the science of the terrestrial upper atmosphere, ionosphere and magnetosphere.

J. K. Hargreaves University of Lancaster

Published by the Press Syndicate of the University of Cambridge

The Pitt Building, Trumpington Street, Cambridge CB2 1RP 40 West 20th Street, New York, NY 10011-4211, USA 10 Stamford Road, Oakleigh, Melbourne 3166, Australia

© Cambridge University Press 1992

First published 1992 First paperback edition 1995

A catalogue record of this book is available from the British Library

Library of Congress cataloguing in publication data

Hargreaves, J. K. (John Keith), 1930 -

The solar-terrestrial environment: an introduction to geospace - the science of the terrestrial upper atmosphere, ionosphere and magnetosphere / J. K. Hargreaves. p. cm. (Cambridge Atmospheric and Space Science Series, 7)

Includes index.

ISBN 0 521 32748 2 hardback ISBN 0 521 42737 1 paperback

Transferred to digital printing 2003

Contents

Preface

Introduction The sun and the solar wind

The atmosphere and the ionosphere

Geomagnetic field and magnetosphere

Nomenclature Summary

2 The physics of geospace 2.1

Useful units and fundamental constants Properties of gases

Gas laws Thermal equilibrium

Continuit y

Collisions Diffusion

Magnetoplasma

Electric and magnetic energy Gyrofrequenc y Betatro n acceleratio n

Plasma frequency Debye length

Frozen-in field E x B drift Fermi acceleration

Waves

Phase velocity Refractive index Group velocity Polarizatio n Energy density

vii viii Contents

2.5 Radio waves in an ionized medium 25 2.5.1 Magneto-ionic theory and the Appleton equation 25 2.5.2 Reflection of an HF radio wave from the ionosphere 27 2.5.3 Partial reflection at a sharp boundary 28 2.5.4 Full wave solutions 29

2.6 Radio propagation through an irregular plasma 29 2.6.1 Introduction 29 2.6.2 Diffraction by a thin screen of weak irregularities 30 2.6.3 Fresnel zone effects 3 2.6.4 Diffraction by strong irregularities 35

2.7 More waves in plasmas 35 2.7.1 Hydromagnetic and magnetosonic waves 35 2.7.2 Whistler and ion-cyclotron waves 36 2.7.3 Electron-acoustic and ion-acoustic waves 39

2.8.4 Kelvin-Helmholtz instability 43 Further reading 43

3 Techniques for observing geospace 4 3.1 The importance of observations 4

3.2 Direct sensing of a gaseous medium 45 3.2.1 Direct measurements of the neutral atmosphere 46 3.2.2 Langmuir probe and derivatives 49 3.2.3 Impedance and resonance probes 52 3.2.4 Mass spectrometers 53

3.3 Radiation sensors 54 3.3.1 Energetic particle detectors 5 3.3.2 Optical and other electromagnetic receivers 5 3.3.3 Magnetometers and electric field sensors 57 3.4 Indirect sensing of the neutral atmosphere 58

3.4.1 Falling spheres and dragging satellites 58 3.4.2 The measurement of upper atmosphere winds 61

Ionospheric modification Plasma and beam injection

Heat injection

Wave injection Water and hydrogen injection

Further reading

The neutral atmosphere

Vertical structure

Nomenclature of atmospheric vertical structure Hydrostati c equilibriu m The exosphere Heat balance and vertical temperature profile Compositio n

Winds and tides Introductio n

The measurement of high-altitude winds Winds in the stratosphere and mesosphere Thermospheric tides

Waves propagating in the neutral air Theory of acoustic-gravity waves

Observation s

Standard atmospheres and models Further reading

The solar wind and the magnetosphere

Introduction

Solar radiations Solar electromagnetic radiation The phenomenon of the solar flare Radio emissions from the Sun Solar activity cycles Proton emissions

The solar wind

Discovery Theory of the solar wind Properties of the solar wind Interplanetary magnetic field and sector structure The coronal hole and fast solar streams

The geomagnetic cavity The geomagnetic field

The magnetopause The magnetosheath and the shock The polar cusps The magnetotail

Circulation of the magnetosphere Circulatio n pattern s

Field merging in the neutral sheet and at the magnetopause Magnetospheric electric fields

Contents ix x Contents

5.8 Magnetospheric current systems 189 5.8.1 The magnetopause current 190 5.8.2 The tail current 191 5.8.3 The ring current 191 5.8.4 Birkeland currents 194 5.9 Substorms in the magnetosphere 196 5.9.1 Consequences of intermittent merging 196 5.9.2 Substorm triggering and the influence of the IMF 200

5.9.3 Substorm currents 201 5.10 Magnetospheres of other planets 202 Further reading 205

6 Principles of the ionosphere at middle and low latitudes 208 6.1 Introduction 208

Principles The Chapman production function

Ionization by energetic particles Principles of chemical recombination Vertical transport

Chemical aeronomy

Introduction E and Fl regions F2 region and protonosphere D region

Principles of airglow

Charged particle motions and electrical conductivity

Introduction Particle motion in a magnetic field in the presence of collisions Responses to a neutral-air wind Response to an electric field Conductivity

Further reading

7 Ionospheric phenomena at middle and low latitudes 7.1

Observed behaviour of the mid-latitude ionosphere

E region and sporadic-E

Fl region F2 region and its anomalies

D region Effects of solar flares

Contents xi

7.2 Ionospheric electric currents 272 7.2.1 Generation of global ionospheric currents 272

7.2.4 Ion drag effects 275 7.3 Peculiarities of the low latitude ionosphere 276

7.4.2 Magnetic storm and the Dst index 279 7.4.3 The F-region ionospheric storm 279

7.4.4 D-region storms 285 7.4.5 Winter anomaly of radio absorption 289 7.5 Irregularities 295 7.5.1 Scintillations 295 7.5.2 Scintillation drifts 300 7.5.3 Spread-F, bubbles and F-region irregularities at low latitude 302 7.5.4 Irregularities in the equatorial electrojet 303 7.5.5 Travelling ionospheric disturbances 305 Further reading 310

8 The ionosphere at high latitude 312

8.1 Dynamics of the polar ionosphere 312 8.1.1 F-region circulation 312 8.1.2 Interaction with the neutral air 315 8.1.3 The S J current system 317 8.1.4 Polar wind 318 8.1.5 The polar cusps 319 8.1.6 Troughs 321

8.4.1 Magnetic bays 341 8.4.2 Auroral electrojets 342 8.4.3 Magnetic indices 345 8.4.4 Substorm in the luminous aurora 346 8.4.5 The unity of auroral phenomena 348 xii Contents

8.5 Polar cap events 351 8.5.1 Introduction 351 8.5.2 Propagation from Sun to Earth 353 8.5.3 Proton propagation in the magnetosphere - Stormer theory 355 8.5.4 Atmospheric effects of solar protons 359 Further reading 362

9 Magnetospheric waves 364 9.1 Wave generation by magnetospheric particles 364

9.4 Effects of waves on particles 379 9.4.1 Particle precipitation by waves 379 9.4.2 The Trimpi event 381 9.4.3 Controlled injection of whistler waves 382 9.4.4 Power-line effects 384 9.4.5 Cyclotron resonance instability 384 Further reading 388

10 Technological application of geospace science 390 10.1 Introduction 390

10.2.1 Radio propagation predictions 392 10.2.2 Satellite communications 395 10.2.3 Navigation, positioning and timekeeping 396 10.2.4 Effects on remote sensing systems 398

10.3 Power lines, pipelines and magnetic prospecting 400

10.4 Space operations 401 10.4.1 Effects on satellites 401 10.4.2 Effects on space travellers 401

10.5 Activity monitoring and forecasting 402

Index 415

Preface

Almost everyone has heard about astronomy though they might not understand it, and almost everyone knows about meteorology even if they cannot spell it. This book is all about the bit in between. Primarily an introductory textbook for students with a background of basic classical physics, it endeavours to describe and explain the phenomena of the terrestrial outer atmosphere and the regions of ' space' nearest to the Earth.

As practitioners will know, this is not a part of the environment that is well known to the general public. The performance of the communications media when attempting to discuss an aurora, or describe the ionosphere, or report the effects of a magnetic storm, is ample testimony to that. Yet, while our subject is a branch of physics and also a branch of geophysics, it may properly be included amongst the environmental sciences as well. Though in the main an academic subject, it is also one which impinges on practical effects of the environment - for instance, communications technology and space activities.

The present book is a sequel to The Upper Atmosphere and Solar-Terrestrial

Relations, which Van Nostrand Reinhold Co. Ltd. published in 1979. I would have liked to get away with merely inserting necessary corrections to the original text, but, unfortunately for me, the science of the upper atmosphere and near space has moved on apace. So I have had to add a good deal of new material, and the whole book has, in fact, been recast - though some of the original matter has been retained (with Van Nostrand Reinhold's kind permission) where it seemed appropriate.

Since the book is introductory (though intended for readers who already have a background in basic physics or engineering), the picture is painted with a broad brush. Explanations are placed in a physical context as far as possible - which means that there have to be equations - but the mathematical treatment is kept to an elementary level. Some of the material is descriptive. The intention is to inform the reader about the basic concepts and methods and to leave him or her with a good idea of what 'geospace' is all about and why it is important, and of the general state of knowledge. The book should be suitable for undergraduates after the first couple of years and for fresh graduate students, and should enable them to move on to the advanced books and the scientific literature. Professionals qualified in other fields who need xiii xiv Preface information about the ionosphere, or about the effects of solar activity, for instance, should also find it useful.

The increased sophistication and greater depth of knowledge in the subject, compared with 10 years ago, have made this book more difficult to write than was my first effort. Bearing in mind the readers for whom it is mainly intended, I have constantly had to compromise between keeping the text at a suitably introductory level and being sufficiently up to date. Critics should also remember, please, that the task has to be completed within a reasonable length - or the product would come out too expensive for them to buy. It will be for the reader(s?) to judge whether the result has the right balance.

One deliberate change is that SI units are now taken as the primary system. We must still remember, nevertheless, that the enormous literature already published in c.g.s. units is not about to self-destruct, and therefore the older system has been included in a secondary role. An introductory book should lead the reader on to the advanced books and the relevent scientific papers, and this includes help with the units.

With the same thought in mind, suggestions for further reading are given after each chapter. The reading lists are in two parts: the first of books or sections of books where the presentation will be tutorial and from which the reader may verify and amplify what I have said; the second comprises mainly review papers which treat the topics in greater detail and which present the state of knowledge at the time they were written. I expect someone's favourite review will have been omitted; if so I can only plead that the lists have to be limited in length and that the selection is necessarily a personal one and in no sense definitive.

The principal material is contained in Chapters 4 to 9, which between them discuss the neutral and the ionized upper atmosphere, the magnetosphere, structures, dynamics, disturbances and irregularities. Chapter 2 summarizes points of basic physics which may or may not have been encountered before, but which are particularly important for the comprehension of the succeeding material. Chapter 3 describes the methods of geospace investigation, dwelling on the physical principles rather than the hardware. Practical applications are discussed in Chapter 10. Some paragraphs have been set in smaller type, and these can be omitted at a first reading without loss of continuity.

I have often been surprised by the degree of cooperation that goes on between scientists, who so often seem actually pleased to assist one another, expecting nothing other than reciprocation in return. I have benefited from that attitude in preparing this text. In particular I wish to thank Sa. Basu, Su. Basu, K. Bullough, M. J. Buonsanto, J. D. Craven, M. A. Clilverd, R. F. Donnelly, G. Enno, H. Gough, C. Haldoupis, M. A. Hapgood, G. Heckman, R. A. Heelis, R. B. Home, R. D. Hunsucker, U. S. Inan, J. D. Mathews, M. H. Rees, P. H. Reiff, A. S. Rodger, H. H. Sauer, A. J. Smith, H. C. Stenbaek-Nielsen, R. D. Stewart, D. M. Willis and K. C. Yeh, each of whom has helped in some specific way, for example by providing an unpublished diagram or by helping me with some scientific point.

(Parte 1 de 6)

Comentários