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  • Society of Geomagnetism and Earth, Planetary and Space Sciences  (3)
  • Ottawa : Geological Survey of Canada
  • 1995-1999  (3)
Collection
Publisher
  • Society of Geomagnetism and Earth, Planetary and Space Sciences  (3)
  • Ottawa : Geological Survey of Canada
Years
Year
  • 1
    Publication Date: 1996-01-01
    Description: In the spring of 1994, a survey was carried out to redetermine the position of the North Magnetic Pole (NMP). Observations of declination, inclination, and total intensity were made at eight sites around the expected location of the pole. All observations were corrected for transient variations using data from a variometer set up in the survey area, and data from magnetic observatories at Mould Bay and Resolute Bay. The NMP position was determined by performing a spherical cap harmonic analysis of the corrected data. The computed position of 78.3°N, 104.0°W for 1994.0 was 150 km northwest of the position previously determined in 1984, and showed that the NMP was moving more rapidly than anticipated. The motion of the NMP has changed from a uniform drift of about 9 km/yr, prior to mid-1971, to a uniform acceleration of approximately 0.34 km/yr2, after mid-1971. This change may be related to the widelyreported geomagnetic jerk that occurred in 1969/70.
    Print ISSN: 0022-1392
    Topics: Geosciences
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  • 2
    Publication Date: 1997-01-01
    Description: Several innovations have been introduced in the production of the Canadian Geomagnetic Reference Field (CGRF) for 1995. The secular variation and main field were modelled simultaneously using the recently developed method of main field differences. The degree of the temporal polynomial was varied depending on the spherical cap harmonic spatial degree. Modifications were made to allow the use of scalar, as well as vector, data in the analysis. Use was made of several data sets not used in previous versions of the CGRF, including Project Magnet data, POGS data, low-level scalar aeromagnetic data, and scalar marine data. A spherical cap harmonic model was produced for a spherical cap of 30 radius centred at 65N, 85W. The maximum spatial index of expansion was K= 16, and the maximum temporal expansion was 7. The CGRF results in an error variance to the data over the modelling area that is 19% lower for the main field data and 55% lower for secular variation data than does the IGRF.
    Print ISSN: 0022-1392
    Topics: Geosciences
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  • 3
    Publication Date: 1997-01-01
    Description: Regional spatial-temporal models of the geomagnetic field have been produced by a variety of techniques. Recently, spherical cap harmonic analysis has gained wide acceptance as a means of modelling the magnetic field over a portion of the globe. Time variations of the field are commonly representedby polynomials or trigonometric series. The Canadian Geomagnetic Reference Field for 1995 (CGRF) is an example of a model produced in this manner. There are, however, other techniques that may offer advantages for some applications. The method of natural orthogonal components is one of these. To demonstrate this method, a spatial-temporal model of the geomagnetic field changes over Canada (ROM-Canada) has been produced using North American observatory annual means and Canadian repeat station data. These data were fitted with rectangular Legendre polynomials using natural orthogonal components as the temporal functions. Overall, total-intensity first-differences computed from the CGRF and ROM-Canada model the observed first-differences with comparable accuracy. ROM-Canada appears to be somewhat more accurate in the centre of the modelling area, but less accurate near the edges. Moreover, the ROM-Canada models of the vector components are less accurate than the CGRF.
    Print ISSN: 0022-1392
    Topics: Geosciences
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