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23 records · Page 2Linked to original sources
USGS1992

Analysis of geomagnetic secular variation during 1980-1985 and 1985- 1990, and geomagnetic models proposed for the 1991 revision of the International Geomagnetic Reference Field

The secular variation of the main geomagnetic field during the periods 1980-1985 and 1985-1990 was analyzed in terms of spherical harmonics up to the eighth degree and order. Data from worldwide magnetic observatories and the Navy's Project MAGNET aerial surveys were used. The resulting pair of secular-variation models was used to update the Definitive Geomagnetic Reference Field (DGRF) model for 1980, resulting in new main-field models for 1985.0 and 1990.0. These, along with the secular-variation model for 1985-1990, were proposed for the 1991 revision of the International Geomagnetic Reference Field (IGRF).

Journal of Geomagnetism & Geoelectricity↗
USGS1992

Evaluation of models proposed for the 1991 revision of the International Geomagnetic Reference Field

The 1991 revision of the International Geomagnetic Reference Field (IGRF) comprises a definitive main-field model for 1985.0, amain-field model for 1990.0, and a forecast secular-variation model for the period 1990-1995. The five 1985.0 main-field models and five 1990.0 main-field models that were proposed have been evaluated by comparing them with one another, with magnetic observatory data, and with Project MAGNET aerial survey data. The three secular-variation models that were proposed have also been compared with one another, and with estimates of recent rates of change at the observatories. The comparisons indicate that the main-field models proposed by IZMIRAN, and the secular-variation model proposed jointly by the British Geological Survey and the U. S. Naval Oceanographic Office, should be assigned relatively lower weight in the derivation of the new IGRF models.

Journal of Geomagnetism & Geoelectricity↗
USGS1994

Magnetic and gravity constraints on forearc upper crustal structure and composition, offshore northeast Japan

Marine magnetic and gravity data from the northeast Japan forearc offer insight to the subsurface structure, density and magnetization from which geologic interpretations and tectonic reconstructions can be made. Positive marine magnetic anomalies, on-land geology, drill hole data, and 2-1/2-dimensional models reveal that Kitakami plutons and possibly their associated volcanic rocks constitute part of the modern forearc basement and lie 100-150 km further east than previously thought. A method to create magnetization and density contrast maps was employed to produce a three-dimensional picture of the forearc basement rock properties averaged over a 14-km thickness. -Author

Pacific Ocean↗
USGS1986

Fourier power spectra of the geomagnetic field for circular paths on the Earth's surface.

The Fourier power spectra of geomagnetic component values, synthesized from spherical harmonic models, have been computed for circular paths on the Earth's surface. They are not found to be more useful than is the spectrum of magnetic energy outside the Earth for the purpose of separating core and crustal sources of the geomagnetic field. The Fourier power spectra of N and E geomagnetic components along nearly polar great circle paths exhibit some unusual characteristics that are explained by the geometric perspective of Fourier series on spheres developed by Yee.

Journal of Geomagnetism & Geoelectricity↗