The world magnetic survey

The history of geomagnetism began around the year 1000 with the discovery in China of the magnetic compass. Methodical studies of the Earth's field started in 1600 with William Gilbert's De Magnete [Gilbert, 1600] and continued with the work of (among others) Edmond Halley, Charles Augustin de Coulomb, Carl Friedrich Gauss, and Edward Sabine. The discovery of electromagnetism by Hans Christian Oersted and André‐Marie Ampére led Michael Faraday to the notion of fluid dynamos, and the observation of sunspot magnetism by George Ellery Hale led Sir Joseph Larmor in 1919 to the idea that such dynamos could sustain themselves naturally in convecting conducting fluids. From that came modern dynamo theory, of both the solar and terrestrial magnetic fields. Paleomagnetic studies revealed that the Earth's dipole had undergone reversals in the distant past, and these became the critical evidence in establishing plate tectonics. Finally, the recent availability of scientific spacecraft has demonstrated the intricacy of the Earth's distant magnetic field, as well as the existence of magnetic fields associated with other planets and with satellites in our solar system.

Section: Explorations and Surveysmentioning

confidence: 99%

A Millennium of Geomagnetism

Stern

2002

“…1. Instrumentation, .for example, magnetometers [Heppner, 1963;Ness, 1970] 2. Wave phenomena in the magnetosphere [Shewhan, 1979], including whistlers [Helliwell, 1965;Alpert, 1980; see also BH-1], auroral kilometric radiation [Gurnett, 1974], micropulsations [Hughes, 1983; Lanze-rotti and Southwood, 1979], 3/2 cyclotron frequency emissions, auroral hiss, and other modes.…”

Section: Other Areasmentioning

confidence: 99%

A brief history of magnetospheric physics during the space age

Stern¹

1996

After 1958, when scientific satellites began exploring the Earth magnetic environment, many puzzling phenomena could be directly examined, especially the polar aurora and disturbances of the Earth's magnetic field [see Stern, 1989a]. The notion of the solar wind, also introduced in 1958, helped clarify the role of the Sun in driving such phenomena. The large‐scale structure of the magnetosphere, the space region dominated by the Earth's magnetic field, was gradually revealed within the next decade: its trapped particles, its boundary, and its long magnetic tail on the nightside. Inevitably, however, at a more fundamental level, the new discoveries led to new questions about the transfer of energy, the flow patterns of plasmas and electric currents, the acceleration of the aurora, and transient events such as magnetic substorms and storms, which energized ions and electrons. Though significant progress has occurred in some of these areas, many unresolved issues still remain. This review outlines the history of magnetospheric research, draws some general conclusions, and provides an extensive bibliography.

“…Attention should be given to the factor a outside the summation, intended to give the coefficients g,•" and h,• " the dimensions of magnetic field: as a consequence, such coefficients are generally given in units of gauss or gammas (1 •, = 10 -5 G). The form given in (11), involving real coefficients, is preferred in geomagnetic research over the one used in mathematical treatments, where the last factor in each term of (11) is expressed in terms of Chapman and Bartels, 1940;Heppner, 1963;Kaula, 1968;Stacey, 1969;Zmuda, 1973].…”

Section: Spherical Harmonicsmentioning

confidence: 99%

“…A very comprehensive review of early analyses of the main field has been compiled by McDonald and Gunst [1967], and some early results are also given by Chapman and Barrels [1940]. More recent field models have been listed by Heppner [1963] (Gaussian normalization) and by Vestine [1960] (Schmidt normalization). Cain [1971] reviewed some other recent work and analyzed problems which arise in connection with field mapping by satellite.…”

Section: Geomagnetic Modelsmentioning

confidence: 99%

Representation of magnetic fields in space

Stern¹

1976

115

Several mathematical methods which are available for the description of magnetic fields in space are reviewed. Examples of the application of such methods are given, with particular emphasis on work related to the geomagnetic field, and their individual properties and associated problems are described. The methods are grouped in five main classes: (1) methods based on the current density j, (2) methods using the scalar magnetic potential γ, (3) toroidal and poloidal components of the field and spherical vector harmonics, (4) Euler potentials, and (5) local expansions of the field near a given reference point. Special attention is devoted to models of the magnetosphere, to the uniqueness of γ as derived from observed data, and to the L parameter.