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N.W. Peddie

Publications and source records attributed to N.W. Peddie.

At least 37 records · Page 2Linked to original sources
USGS1987

A model of geomagnetic secular variation for 1980-1983

We developed an updated model of the secular variation of the main geomagnetic field during 1980 through 1983 based on annual mean values for that interval from 148 worldwide magnetic observatories. The model consists of a series of 80 spherical harmonics, up to and including those of degree and order 8. We used it to form a proposal for the 1985 revision of the International Geomagnetic Reference Field (IGRF). Comparison of the new model, whose mean epoch is approximately 1982.0, with the Provisional Geomagnetic Reference Field for 1975-1980 (PGRF 1975), indicates that the moment of the centered-dipole part of the geomagnetic field is now decreasing faster than it was 5 years ago. The rate (in field units) indicated by PGRF 1975 was about -25 nT a-1, while for the new model it is -28 nT a-1. ?? 1987.

Physics of the Earth and Planetary Interiors↗
USGS1987

Assessment of models proposed for the 1985 revision of the international geomagnetic reference field

Geomagnetic measurements from land, marine and aerial surveys conducted in the years 1945-1964 were used to test the 14 models proposed as additions, for that period, to the series of definitive geomagnetic reference field (DGRF) models. Overall, NASA's 'SFAS' models and the BGS (British Geological Survey) models agree best with these data. Comparisons of the two proposed definitive main-field models for 1980.0, with each other and with the existing IGRF 1980 main-field model, show mostly close agreement, with the greatest absolute differences (several tens of nanotesla) occurring in the region of Antarctica. Comparison of the the three proposed forecast secular-variation models for 1985-1990 with estimates of recent rates of change at 148 magnetic observatories shows that the IZMIRAN (U.S.S.R.) and USGS models are in closest agreement with these data. ?? 1987.

Physics of the Earth and Planetary Interiors↗
USGS1985

An assessment of the near-surface accuracy of the international geomagnetic reference field 1980 model of the main geomagnetic field

The new International Geomagnetic Reference Field (IGRF) model of the main geomagnetic field for 1980 is based heavily on measurements from the MAGSAT satellite survey. Assessment of the accuracy of the new model, as a description of the main field near the Earth's surface, is important because the accuracy of models derived from satellite data can be adversely affected by the magnetic field of electric currents in the ionosphere and the auroral zones. Until now, statements about its accuracy have been based on the 6 published assessments of the 2 proposed models from which it was derived. However, those assessments were either regional in scope or were based mainly on preliminary or extrapolated data. Here we assess the near-surface accuracy of the new model by comparing it with values for 1980 derived from annual means from 69 magnetic observatories, and by comparing it with WC80, a model derived from near-surface data. The comparison with observatory-derived data shows that the new model describes the field at the 69 observatories about as accurately as would a model derived solely from near-surface data. The comparison with WC80 shows that the 2 models agree closely in their description of D and I near the surface. These comparisons support the proposition that the new IGRF 1980 main-field model is a generally accurate description of the main field near the Earth's surface in 1980. ?? 1985.

Physics of the Earth and Planetary Interiors↗
USGS1982

International geomagnetic reference field 1980: a report by IAGA Division I working group.

Describes the recommendations of the working group, which suggested additions to IGRF because of the cumulative effect of the inevitable uncertainties in the secular variation models which had led to unacceptable inaccuracies in the IGRF by the late 1970's. The recommendations were accepted by the International Association of Geomagnetism and Aeronomy on August 15, 1981 at the 4th Scientific Assembly, Edinburgh. An extended table sets out spherical harmonic coefficients of the IGRF 1980.-R.House

Geophysical Journal of the Royal Astronomical Soci↗
USGS1982

A Proposed Model for the International Geomagnetic Reference Field-1965

A best current model of the main geomagnetic field is presented as a response to a need for an “International Geomagnetic Reference Field”. This model is described by a series of 120 spherical harmonic coefficients and their first and second time derivatives from an epoch 1960.0. It was derived from a sample of all magnetic survey data available from the interval 1900-1964 plus a recent global distribution of preliminary total field observations from the OGO-2 (1965-81A) spacecraft for epoch 1965.8. A duplicate data selection was made and the resulting field model compared with the first to help evaluate the minimum error. It was noted that the root —mean—square difference between the two models was about 30γ in the force components, 0.04 degrees in dip and 0.3 degrees in declination at the earth's surface for 1965.0.

Journal of Geomagnetism & Geoelectricity↗
USGS1982

International Geomagnetic Reference Field

In August 1981 the International Association of Geomagnetism and Aeronomy revised the International Geomagnetic Reference Field (IGRF). It is the second revision since the inception of the IGRF in 1968. The revision extends the earlier series of IGRF models from 1980 to 1985, introduces a new series of definitive models for 1965-1975, and defines a provisional reference field for 1975-1980. The revision consists of: (1) a model of the main geomagnetic field at 1980.0, not continuous with the earlier series of IGRF models, together with a forecast model of the secular variation of the main field during 1980-1985; (2) definitive models of the main field at 1965.0, 1970.0, and 1975.0, with linear interpolation of the model coefficients specified for intervening dates; and (3) a provisional reference field for 1975-1980, defined as the linear interpolation of the 1975 and 1980 main-field models. The new models are series of solid spherical harmonics up to and including the tenth degree and order for the main-field models, and up to and including the eighth degree and order for the secular variation model. The models were derived from three sets of proposed models by taking weighted means. The weights were chosen according to the apparent accuracy of the proposed models. A brief history of the IGRF, a review of basic formulas, and a set of world contour maps of the geomagnetic elements based on the IGRF 1980 model are included.

Journal of Geomagnetism & Geoelectricity↗
USGS1982

Assessment of models proposed for the 1981 revision of the IGRF

For the second revision of the International Geomagnetic Reference Field (IGRF), the U. S. National Aeronautics and Space Administration (NASA), the U. K. Institute of Geological Sciences (IGS), and the U. S. Geological Survey (USGS) submitted proposed models of the Earth's main magnetic field at 1965.0, 1970.0, 1975.0, and 1980.0, and its secular variation during 1980-1985. We assessed the proposed models by comparing them with annual mean values from worldwide magnetic observatories, data for 1978-1980 from 63 U. S. magnetic repeat stations, and rates-of-change values for worldwide magnetic observatories for 1965-1985 that were derived from straight lines fitted to annual means for five-year intervals. We also mutually compared the 1980 models.

Journal of Geomagnetism & Geoelectricity↗