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Preface to Volume 4
Preface to Volume 4
It is fitting that this last volume in the four-volume series on geomagnetism should be completed in 1990, exactly 50 years after Chapman and Bartels pubhshed their two-volume work on geomagnetism that has remained a classic ever since. Like most branches o f science, there has been an explo sive increase in our knowledge o f geomagnetism, particularly in the related field of upper-atmospheric physics (aeronomy). This is in part due to the advent o f space probes which have enabled us to make observations far beyond the orbit o f the Earth. Today the concept o f the solar wind, the magnetosphere and the Van Allen radiation behs are accepted as common knowledge, yet in Chapman and Bartels' time they were unknown and much o f their work on magnetic storms and other phenomena have had to be completely rewritten. This final volume begins with a detailed account o f the solar wind by P. A . Isenberg—its large-scale properties, microstructure, discontinuities and shock waves. This is followed by three chapters on the magnetosphere. M . Schulz discusses its general configuration, radiation belts, cosmic rays and plasma composition. G . Paschmann then reviews our knowledge o f the magnetopause, and T . W . Speiser the magnetotail. A subject o f increasing importance is the neutral atmosphere and this is discussed in detail by A . D . Richmond—its structure, composition and dynamics, together with gravity waves and atmospheric tides. Comprehensive accounts are given by J. C. Samson on geomagnetic micropulsations and plasma waves in the Earth's magnetosphere and by R . L . McPherron on physical processes pro ducing magnetospheric substorms and magnetic storms. These last two chapters concern phenomena recorded at the Earth's surface even before the time o f Chapman and Bartels, but not understood. Samson and McPherron also relate the events to other upper-atmospheric phenomena. The volume ends with a chapter by T . J. Halhnan on the a u r o r a phenomena also long observed at the Earth's surface, but again not understood. The whole o f the first volume o f Chapman and Bartels' work is devoted
χ
PREFACE TO VOLUME
4
to observations o f the Earth's magnetic field—the main field and transient variations. Their second volume contains two parts—the first deals with the analysis and synthesis o f geomagnetic data, and it is only in the second part that any attempt is made to develop physical theories o f geomagnetic phenomena. Only 12 pages out o f more than 950 in their two volumes are devoted to theories o f the main field and secular variation. In contrast, in Volume 2 o f this series, more than 120 pages are given to the kinematics and dynamics o f the main field—and this follows 180 pages on the magnetohydrodynamics o f the Earth's core. Magnetohydrodynamics has dominated the physics o f much o f geomagnetism today. The dynamo theory o f the main field, generally now accepted, although not fully understood, was not proposed by E. C . Bullard and W . M . Elsasser until the late 1940s some 10 years after the publication o f Chapman and Bartels' book. Theories o f quiet solar variations (Sq) and lunar variations ( L ) were better understood, and ionospheric dynamos were discussed by Chapman and Bartels. Another area which has developed since the time o f Chapman and Bartels is rock magnetism and palaeomagnetism which plays a key role in tectonics today—over 250 pages are devoted to these subjects in Volume 3. Reversals o f the Earth's magnetic field and magnetic stratigraphy are also 'new' topics today and attract the attention o f theoretical physicists working on the main field and geologists. N o r is interest in geomagnetism confined to the Earth. Magnetism has become one o f the main tools for investigating the interiors o f other planets, and in Volume 2 over 250 pages discuss the magnetism of the other planets, the M o o n and meteorites. The four volumes thus represent in a very real sense the way in which geomagnetism, the oldest subject o f scientific enquiry, has developed in the last 50 years from its early beginnings nearly 400 years ago (the first scientific textbook was De Magnete, published by Wilham Gilbert in 1600). J. A.
JACOBS
It is fitting that this last volume in the four-volume series on geomagnetism should be completed in 1990, exactly 50 years after Chapman and Bartels pubhshed their two-volume work on geomagnetism that has remained a classic ever since. Like most branches o f science, there has been an explo sive increase in our knowledge o f geomagnetism, particularly in the related field of upper-atmospheric physics (aeronomy). This is in part due to the advent o f space probes which have enabled us to make observations far beyond the orbit o f the Earth. Today the concept o f the solar wind, the magnetosphere and the Van Allen radiation behs are accepted as common knowledge, yet in Chapman and Bartels' time they were unknown and much o f their work on magnetic storms and other phenomena have had to be completely rewritten. This final volume begins with a detailed account o f the solar wind by P. A . Isenberg—its large-scale properties, microstructure, discontinuities and shock waves. This is followed by three chapters on the magnetosphere. M . Schulz discusses its general configuration, radiation belts, cosmic rays and plasma composition. G . Paschmann then reviews our knowledge o f the magnetopause, and T . W . Speiser the magnetotail. A subject o f increasing importance is the neutral atmosphere and this is discussed in detail by A . D . Richmond—its structure, composition and dynamics, together with gravity waves and atmospheric tides. Comprehensive accounts are given by J. C. Samson on geomagnetic micropulsations and plasma waves in the Earth's magnetosphere and by R . L . McPherron on physical processes pro ducing magnetospheric substorms and magnetic storms. These last two chapters concern phenomena recorded at the Earth's surface even before the time o f Chapman and Bartels, but not understood. Samson and McPherron also relate the events to other upper-atmospheric phenomena. The volume ends with a chapter by T . J. Halhnan on the a u r o r a phenomena also long observed at the Earth's surface, but again not understood. The whole o f the first volume o f Chapman and Bartels' work is devoted
χ
PREFACE TO VOLUME
4
to observations o f the Earth's magnetic field—the main field and transient variations. Their second volume contains two parts—the first deals with the analysis and synthesis o f geomagnetic data, and it is only in the second part that any attempt is made to develop physical theories o f geomagnetic phenomena. Only 12 pages out o f more than 950 in their two volumes are devoted to theories o f the main field and secular variation. In contrast, in Volume 2 o f this series, more than 120 pages are given to the kinematics and dynamics o f the main field—and this follows 180 pages on the magnetohydrodynamics o f the Earth's core. Magnetohydrodynamics has dominated the physics o f much o f geomagnetism today. The dynamo theory o f the main field, generally now accepted, although not fully understood, was not proposed by E. C . Bullard and W . M . Elsasser until the late 1940s some 10 years after the publication o f Chapman and Bartels' book. Theories o f quiet solar variations (Sq) and lunar variations ( L ) were better understood, and ionospheric dynamos were discussed by Chapman and Bartels. Another area which has developed since the time o f Chapman and Bartels is rock magnetism and palaeomagnetism which plays a key role in tectonics today—over 250 pages are devoted to these subjects in Volume 3. Reversals o f the Earth's magnetic field and magnetic stratigraphy are also 'new' topics today and attract the attention o f theoretical physicists working on the main field and geologists. N o r is interest in geomagnetism confined to the Earth. Magnetism has become one o f the main tools for investigating the interiors o f other planets, and in Volume 2 over 250 pages discuss the magnetism of the other planets, the M o o n and meteorites. The four volumes thus represent in a very real sense the way in which geomagnetism, the oldest subject o f scientific enquiry, has developed in the last 50 years from its early beginnings nearly 400 years ago (the first scientific textbook was De Magnete, published by Wilham Gilbert in 1600). J. A.
JACOBS