Physics of the Earth's Space Environment

Transcription

1 Physics of the Earth's Space Environment

2 Gerd W. Prolss Physics of the Earth's Space Environment An Introduction With 263 Figures Including 4 Color Figures ~ Springer

3 Professor Dr. Gerd W. Pro Iss Universitat Bonn Institut fiir Astrophysik und Extraterrestrische Forschung Auf dem Hiigel Bonn, Germany Translated by: Dr. Michael Keith Bird Universitat Bonn Institut fiir Radioastronomie Auf dem Hiigel Bonn, Germany Cover picture: Dayglow and aurora imaged from the DEI satellite at an altitude of about 20,000 km. Further information may be found in Sections and 7.4 (L.A. Frank, University ofiowa). Library of Congress Control Number: ISBN-13: e-isbn-13: DOl: / This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer. Violations are liable to prosecution under the German Copyright Law. Springer is a part of Springer Science+ Business Media springeronline.com Springer-Verlag Berlin Heidelberg 2004 Softcover reprint of the hardcover 1St edition 2004 The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Print data prepared by LE-TeX Jelonek, Schmidt & Viickler GbR, Leipzig Cover design: Erich Kirchner, Heidelberg Printed on acid-free paper 57/3141/ts

4 Preface This book was written for readers interested in learning about the disciplines, methods and results of space research, perhaps because they happened upon the field during the course of their higher education or professional career, or perhaps because they simply feel an urge to know more about the space environment of the Earth. The present monograph is based on lectures covering the same topic, which have been held regularly over the past years at the University of Bonn. Like the lecture series, the book is directed at a relatively broad group of students and interested laypersons, the only prerequisite being knowledge of fundamental physics and mathematics, as usually acquired from introductory college courses in science or engineering curricula. More specific knowledge is derived in association with each phenomenon considered. These derivations are kept as simple as possible, adhering to the principle that, when conflicts arise, physical insight is preferable to mathematical precision. As a rule, I strived to avoid the trite phrase 'It may be easily shown that... ' and tried to present all derivations in readily verifiable steps, even if this may seem somewhat tedious to the more advanced readers. Also serving clarity and insight are the many illustrations, which do indeed often say more than 'a thousand words'. Our knowledge of the Earth's space environment has grown exponentially during the last few decades and an attempt to cover all aspects of the field would extend way beyond the scope of an introductory text. Acknowledging this fact, the book does contain some unavoidable gaps and even topics of special interest to the author have been omitted for lack of space. In particular, measurement techniques, although constituting a cornerstone of space research (and of physics in general), could only be described in passing. We content ourselves here with presenting the experimental results and then trying to explain the underlying physics on the basis of simple reasoning and argumentation. It is fair to say that this introduction to the field will have fulfilled its purpose if its readers are inspired to investigate a topic in more detail on their own, referring to the pertinent literature. It is a pleasure to thank all those who directly or indirectly participated in the preparation and production of this book. I would like to thank my mentor W. Priester and my colleagues M. Roemer, H.J. Fahr and H. Volland for their support and the pleasant work environment in our institute. Parts

5 VI Preface of this book were reworked during a lecture series presented at the University of Innsbruck and during a research fellowship at the University of Nagoya. I extend my sincere gratitude here to colleagues M. Kuhn and Y. Karnide for the invitations. Valuable suggestions and various forms of assistance were provided by colleagues and coworkers S.J. Bauer, M.K. Bird, H. Fichtner, C. Lay, C.A. Loewe, K. Schriifer, R. Treumann and S. Werner. I would like to make special mention of contributions from S. Noel, M. Kilbinger, B. Kuhlen, J. Pielorz and B. Winkel, who competently and patiently edited the manuscript into its final form. Without their help this book would surely have been a never ending story. Bonn, December 2003 Gerd W. Prolss

6 Contents 1. Introduction Definitions and Constraints Scope and Organization of the Material Brief History of Space Research Neutral Upper Atmosphere State Parameters of Gases and their Gas Kinetic Interpretation Definition and Derivation of Gas Kinetic Parameters Macroscopic State Parameters Height Profiles of the State Parameters Barospheric Density Distribution Ae[ostatic Equation Pressure Gradient Force Barometric Law Heterospheric Density Distribution Gas Kinetics of the Barometric Law Transition from Homosphere to Heterosphere Atomic Oxygen and Hydrogen Exospheric Density Distribution Exobase Height Escape Velocity Velocity Distribution in Gases Escape Flux and Stability of the Atmosphere Exospheric Density Distribution Absorption of Solar Radiation Energy Origin and Characteristics of Solar Radiation Interior Structure of the Sun Solar Atmosphere Radiation Spectrum Variation of the Radiation Intensity Extinction of Solar Radiation in the Upper Atmosphere Absorption Processes Extinction of Radiation in Gases

7 VIII Contents Extinction of Radiation in the Upper Atmosphere Energy Deposition from Radiation Absorption Heating and Temperature Profile Heat Production Temperature Increase from Heating Heat Losses by Radiative Cooling Heat Losses by Molecular Heat Conduction Heat Balance Equation and Temperature Profile Estimate of the Thermopause Temperature Temperature and Density Variations Airglow Thermospheric Winds Diurnal Wind Circulation: Observations Inventory of Relevant Forces Momentum Balance Equation Calculation of Thermospheric Winds Atmospheric Waves Wave Parameters Acoustic Waves Buoyancy Oscillations Gravity Waves Ionosphere Height Profile of Ionospheric State Parameters Ionization Production and Loss Ionization Production Ionization Losses Chemical Composition Density Profile in the Lower Ionosphere Density Balance Equation Density Profile in the E Region Density Profile in the Lower F Region Density Profile in the Upper Ionosphere Barometric Density Distribution Polarization Field Transport Equilibrium Production-Generated Downward Current Density Maximum and Ionospheric Time Constants Ionospheric Time Constants..., Ionization Density Maximum Ionoexosphere Systematic Variations of the Ionization Density Radio waves in the Ionosphere Plasma Oscillations The Ionosphere as a Dielectric

8 Contents IX The Ionosphere as a Conducting Reflector Magnetic Field Influence Magnetosphere Fundamentals The Geomagnetic Field Near the Earth Charged Particle Motion in the Geomagnetic Field Gyromotion Oscillatory (Bounce) Motion Drift Motion Composite Charge Carrier Motion Coulomb Collisions Particle Populations in the Inner Magnetosphere Radiation Belt Ring Current Plasmasphere The Distant Geomagnetic Field Configuration and Classification Dayside Magnetopause Currents Current System of the Geomagnetic Tail Particle Populations in the Outer Magnetosphere Magnetotail Plasma Sheet Magnetotail Lobe Plasma Magnetospheric Boundary Layer Magnetoplasma Waves in the Magnetosphere Interplanetary Medium The Solar Wind Properties of the Solar Wind at the Earth's Orbit Gas Dynamic Model Temperature Profile Extended Gas Dynamic Models Exospheric Model Large-Scale Solar Wind Structure in the Ecliptic Solar Wind Outside the Ecliptic Plane Interplanetary Magnetic Field Observations Simple Model of the Interplanetary Magnetic Field Magnetic Field Structure Outside the Ecliptic Heliospheric Current Sheet Sector Structure and B<p Component Interplanetary Electric Field The Interplanetary Medium as a Magnetoplasma Magnetoplasma Waves in the Interplanetary Medium Plasma Acoustic Waves

9 X Contents Alfven Waves Magnetosonic Waves Modification of the Solar Wind by the Bow Shock Formation of the Bow Shock Modification of the Solar Wind by the Bow Shock Results from Model Calculations Pressure Balance at the Magnetopause The Bow Shock as a Plasmadynamic Phenomenon Interaction of the Solar Wind with the Interstellar Medium Energetic Particles in Interplanetary Space Energetic Particles of Galactic Origin Energetic Particles of Interplanetary Origin Energetic Particles of Solar/Planetary Origin Absorption and Dissipation of Solar Wind Energy Topology of the Polar Upper Atmosphere Electric Fields and Plasma Convection Ionospheric Conductivity and Currents Collision Modified Charge Carrier Motion Ionospheric Transverse Conductivity Parallel Conductivity Ionospheric Currents Magnetic Field Effects Aurorae Morphology Dissipation of Auroral Particle Energy Origin of the Auroral Particles Neutral Atmospheric Effects Drift-induced Winds Heating Composition Disturbances Energy Transfer from Solar Wind to Magnetosphere Solar Wind Dynamo Open Magnetosphere Plasma Convection in the Open Magnetosphere Open Magnetosphere with Tail Reconnection Origin of Birkeland Currents Low-Latitude Boundary Layer Dynamo Geospheric Storms Magnetic Storms Regular Variations Magnetic Activity at Low Latitudes Magnetic Activity at High Latitudes Magnetic Activity at Mid-latitudes

10 Contents XI 8.2 Auroral Substorms Magnetospheric Substorms Growth Phase Expansion Phase Thermospheric Storms Composition Disturbances at Mid-latitudes Density Disturbances at Low Latitudes Ionospheric Storms Negative Ionospheric Storms Positive Ionospheric Storms The Sun as the Origin of Geospheric Storms Solar Mass Ejections and Magnetic Clouds Corotating Interaction Regions Solar Flares Disturbance Effects on Technological Systems A. Formulas, Tables and Derivations A.l Selected Mathematical Formulas A.2 Physical Parameters of the Earth A.3 Planetary Data A.4 Model Atmosphere A.5 Diffusion Equation for Gases A.6 Derivation of the Momentum Balance Equation A.7 Energy Balance Equation of an Adiabatic Gas Flow A.8 Bernoulli Equation A.9 Rankine-Hugoniot Equations A.I0 Maxwell Equations A.ll Curvature of a Dipole Field Line A.12 Gradient Drift Velocity A.13 System of Equations for Ideal Magnetoplasmadynamics A.13.1 Balance Equations of a Magnetoplasma A.13.2 Maxwell Equations and the Generalized Ohm's Law A.13.3 Validity Test of the Approximations A.14 Two Theorems of Magnetoplasmadynamics A.15 Magnetoplasma Waves A.15.1 Simplification of the System of Equations A.15.2 Wave Propagation Parallel to a Magnetic Field A.15.3 Wave Propagation Perpendicular to a Magnetic Field 494 A.15.4 Validity Test of the Approximations A.16 Plasma Instabilities B. Figure and Table References Index

11 List of Frequently Used Symbols A area ex generic angle; pitch angle i3 magnetic flux density, here denoted as magnetic field Boo Earth's equatorial surface magnetic field intensity c random velocity (thermal velocity, peculiar velocity) Co speed of light c P ' Cv specific heat capacity at constant pressure, volume X zenith angle; spiral angle d thickness; transport term in the equations of balance D diffusion coefficient; declination e electron e elementary charge; base of the natural logarithm E energy f electric field eo permittivity of free space er relative permittivity (dielectric constant) f degree of freedom; frequency f distribution function F force F* force per unit volume g gravitational acceleration (ge, gs: terrestrial, solar acceleration) g velocity distribution function G gravitational constant "( adiabatic exponent "(* polytropic index h height (altitude) hp Planck constant h(c) speed (velocity magnitude) distribution function H scale height; horizontal component of the Earth's magnetic field R magnetic field I momentum; inclination i current i* surface current density

12 XIV List of Frequently Used Symbols J current density J x ionization rate coefficient for the species X k Boltzmann constant ks,t reaction constants K generic constant; eddy diffusion coefficient '" heat conductivity length: loss rate per unit volume l1,2 mean free path A wavelength: geographic, heliographic longitude L shell parameter L induction constant In A Coulomb logarithm rn particle mass Tn" atomic mass unit 1I1 generic mass (AlE, Ais: mass of Earth, Sun); l\lach number M mass number (atomic, molecular) M magnetic dipole moment (ME: Earth; M g : gyromoment) /-Lo permeability of free space n particle number density rite! reference density: index of refraction TL surface normal N number of particles N column density V1,2 collision frequency (va: Coulomb collision frequency) vr2 momentum transfer collision frequency (frictional frequency) W angular velocity; rotation rate Wg Brunt-Vaisala frequency Wa gyro frequency (Lannor frequency) wp plasma frequency DE,S angular rotation rate of Earth, Sun P thermodynamic pressure Pd dynamic pressure Pa magnetic pressure p proton P power cp latitude flux of a scalar quantity <P magnetic flux q charge per particle; production rate per unit volume Q heat Q electrical charge T particle radius: radial distance Ta gyroradius (Lannor radius) f position vector

13 List of Frequently Used Symbols XV RE,Rs Earth's radius, Sun's radius P mass density Pc radius of curvature s distance; species index (e, i, n for electrons, ions and neutral gas particles) 0"1,2 collision, interaction cross section O"A absorption cross section O"B,O"H,O"p Birkeland, Hall and Pedersen conductivities t time T temperature (Too: thermopause or exospheric temperature) T time constant; period; optical thickness i1 bulk velocity U internal energy U voltage particle velocity v vs, VA, vms velocity of sound, Alfven velocity, magnetosonic velocity Vph' VgT phase, group velocity V volume w W probability work; index for eddy parameter x, y, z Cartesian coordinates; (x, fj, z unit vectors); variables