Edward Bullard

Bio: Edward Bullard is an academic researcher from Scripps Institution of Oceanography. The author has contributed to research in topics: Earth's magnetic field & Dynamo theory. The author has an hindex of 2, co-authored 2 publications receiving 515 citations.

The westward drift of the Earth's magnetic field

Abstract: The westward drift of the non-dipole part of the earth's magnetic field and of its secular variation is investigated for the period 1907-45 and the uncertainty of the results discussed. It is found that a real drift exists having an angular velocity which is independent of latitude. For the non-dipole field the rate of drift is 0.18$\pm $0.015 $ ^{\circ} $ /year, that for the secular variation is 0.32$\pm $0.067 $ ^{\circ} $ /year. The results are confirmed by a study of harmonic analyses made between 1829 and 1945. The drift is explained as a consequence of the dynamo theory of the origin of the earth's field. This theory required the outer part of the core to rotate less rapidly than the inner part. As a result of electromagnetic forces the solid mantle of the earth is coupled to the core as a whole, and the outer part of the core therefore travels westward relative to the mantle, carrying the minor features of the field with it.

The Direction of the Earth's Magnetic Field at London, 1570-1975

Abstract: The observations of magnetic declination and dip made in London over the past 400 years comprise one of the longest and most complete series of such data for anywhere in the world. They give an indication of secular change on a time scale intermediate between that of recent observatory measurements and of archaeomagnetic measurements. We have attempted to catalogue all direct measurements of declination and dip, paying particular attention to completeness in the earlier years, and tracing the data to their original source wherever possible. Sufficient details of the observations are given for an assessment of their reliability and accuracy. The data are then corrected to a single site, fitted with a continuous smooth curve, and discussed.

Physics of the Earth

Abstract: Preface 1. Origin and history of the Solar System 2. Composition of the Earth 3. Radioactivity, isotopes and dating 4. Isotopic clues to the age and origin of the Solar System 5. Evidence of the Earth's evolutionary history 6. Rotation, figure of the Earth and gravity 7. Precession, wobble and rotational irregularities 8. Tides and the evolution of the lunar orbit 9. The satellite geoid, isostasy and post-glacial rebound 10. Elastic and inelastic properties 11. Deformation of the crust: rock mechanics 12. Tectonics 13. Convective and tectonic stresses 14. Kinematics of the earthquake process 15. Earthquake dynamics 16. Seismic wave propagation 17. Seismological determination of Earth structure 18. Finite strain and high pressure equations of state 19. Thermal properties 20. The surface heat flux 21. The global energy budget 22. Thermodynamics of convection 23. Thermal history 24. The geomagnetic field 25. Rock magnetism and paleomagnetism 26. Alternative energy sources and natural climate variations: some geophysical background Appendix A. General reference data Appendix B. Orbital dynamics (Kepler's laws) Appendix C. Spherical harmonic functions Appendix D. Relationships between elastic moduli of an isotropic solid Appendix E. Thermodynamic parameters and derivative properties Appendix F. An Earth model: mechanical properties Appendix G. A thermal model of the Earth Appendix H. Radioactive isotopes Appendix I. A geological time scale 2004 Appendix J. Problems References Index.

Four centuries of geomagnetic secular variation from historical records

Abstract: We present a new model of the magnetic › eld at the core{mantle boundary for the interval 1590{1990. The model, called gufm1, is based on a massive new compilation of historical observations of the magnetic › eld. The greater part of the new dataset originates from unpublished observations taken by mariners engaged in merchant and naval shipping. Considerable attention is given to both correction of data for possible mislocation (originating from poor knowledge of longitude) and to proper allocation of error in the data. We adopt a stochastic model for uncorrected positional errors that properly accounts for the nature of the noise process based on a Brownian motion model. The variability of navigational errors as a function of the duration of the voyages that we have analysed is consistent with this model. For the period before 1800, more than 83000 individual observations of magnetic declination were recorded at more than 64000 locations; more than 8000 new observations are for the 17th century alone. The time-dependent › eld model that we construct from the dataset is parametrized spatially in terms of spherical harmonics and temporally in B-splines, using a total of 36512 parameters. The model has improved the resolution of the core › eld, and represents the longest continuous model of the › eld available. However, full exploitation of the database may demand a new modelling methodology.

Geomagnetic paleointensities from radiocarbon‐dated lava flows on Hawaii and the question of the Pacific nondipole low

Abstract: Radiocarbon ages have been published for nine basaltic lava flows on the island of Hawaii; the ages range from 2600 to somewhat older than 17,900 years B.P. By using the Thelliers' method in vacuum, geomagnetic paleointensity values were obtained from eight of the lavas; the ninth proved unsuitable. The paleointensities for the four youngest flows (2600–4600 years B.P.) yield virtual dipole moments (VDM's) that are 20% greater to more than twice the worldwide values for those times obtained by V. Bucha from archeomagnetic data. The dispersion of virtual geomagnetic poles for the eight lavas is 15.5°, appreciably larger than the average for older lava flows on Hawaii. These results contrast with the historic magnetic field in the region of Hawaii, in which both secular variation and nondipole components are very low. At about 10,000 years B.P. the measured VDM is not very different from the long-term worldwide average but differs considerably from a smooth extrapolation of Bucha's average curve. At about 18,000 years B.P. the measured VDM is very low and is associated with an unusually shallow paleomagnetic inclination for the latitude of Hawaii. These new paleointensity and paleodirectional data strongly suggest that sizable nondipole geomagnetic fields have existed in the vicinity of Hawaii at various times during the Holocene epoch and perhaps earlier.

Free Hydromagnetic Oscillations of the Earth's Core and the Theory of the Geomagnetic Secular Variation

Abstract: Free hydromagnetic oscillations of a rotating spherical shell of an incompressible fluid are investigated by means of a simple theoretical model For each spatial harmonic, rotation gives rise to two distinct modes of oscillation, ‘magnetic’ and ‘inertial’, which propagate with different velocities As an application of the theory, it is shown that if the strength of the toroidal magnetic field in the Earth’s core is 100 Oe, then many of the properties of the observed secular changes, including the slow westward drift, of the main geomagnetic field at the Earth’s surface can be accounted for in terms of the interaction of magnetic modes in the core with the Earth’s poloidal magnetic field Concomitant magnetic variations due to inertial modes in the core would, owing to their relatively short periods (several days), fail to penetrate to the surface of the Earth, although the eddy currents induced in the lower mantle by these modes might affect the mechanical coupling between the mantle and the core

The secular variation of Earth's magnetic field

Abstract: Models of the magnetic field at the core–mantle boundary at selected epochs from 1715.0 to 1980.0 reveal novel features in the field at the core. These suggest that the flow of core fluid is coupled to the mantle, and that magnetic diffusion is significant.