Geomagnetic temporal change: 1903-1982, A spline representation.

Langel, R. A.; Kerridge, D. J.; Arraclough, D. R.; Malin, S. R. C.

doi:10.5636/jgg.38.573

Cited by 60 publications

(27 citation statements)

References 38 publications

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“…For comparison with the results of LANGEL et al (1986), we computed the westward drift for coefficients of degree 2 through 5. The results, given in Table 5, agree within about 100 of the results derived by LANGEL et al (1986) and show the same trend toward decreasing drift rate as time progresses. The first approximation of the geomagnetic field is that of the field of a dipole located at the Earth's center and inclined to its axis of rotation.…”

Section: The Modelssupporting

confidence: 77%

“…However, it is far from certain that this rate will continue. A plot of g01 shows (e.g., LANGEL et al, 1986; that its rate of change reached a minimum near 1945 after having reached a maximum of about 30nT/yr at about 1917, i.e., the rate of change of g01 is fluctuating. There is some evidence (e.g., LANGEL et al, 1986) that changes in g01 are correlated with changes in the decade fluctuations in the rate of rotation of the Earth.…”

Section: The Modelsmentioning

confidence: 99%

“…Points inside triangles are the yearly change of the strength of the centered dipole in nT a-1. 1962.5 (DAWSON andLOOMER, 1963);1964.0 (HAINES,19671965.0 (DAWSON andDALGETTY,1966);1970.9 (HAINES andHANNAFORD,1974);1973.5 and 1975.0 (DAWSON and NEWITT, 19781980.0 (DAWSON andNEWITT, 1982b …”

Section: The Modelsmentioning

confidence: 99%

“…(The main-field terms from the GSFC(12/83) model, truncated to degree 10, were adopted as the definitive IGRF for 1980.) The projection to the desired epochs was achieved by using a variation of the spline fitting of LANGEL et al (1986). In the present case, annual secular-variation models were derived from first differences of observatory annual means for the period 1940 to 1980.…”

Section: Use Of a Priori Informationmentioning

confidence: 99%

“…A priori models of degree 8 were needed for all years, so an extrapolation scheme was used to derive degree 7 and 8 terms for 1940 to 1958. In this scheme, a preliminary cubic spline function was fitted to the original secular-variation models (see, e.g., LANGEL et al, 1986). The averages of each of the degree 7 or 8 secular variation coefficients from 1960-1970, as determined from the preliminary spline fit, were then appended to the degree 6 models for 1940 to 1958 to give models of degree 8.…”

Section: Use Of a Priori Informationmentioning

confidence: 99%

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Definitive IGRF models for 1945, 1950, 1955, and 1960.

Langel

Barraclough

Kerridge

et al. 1988

J. geomagn. geoelec

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Definitive internal geomagnetic field models are derived for the epochs 1945, 1950, 1955, and 1960. Each model incorporates all data available to us within a five year period centered on the model epoch. For survey data, weighting was determined by examining the spread of residuals for the data, sorted by source and sorted by location, relative to the previous IGRF models. The solution included local biases for the fixed observatories. An a priori model for each epoch was derived by projecting the GSFC (12/83) model, based on Magsat data, backward in time. This projection was accomplished using a spline fit to annual secular-variation models. The spline coefficients were simultaneously fit to all spherical harmonic secular variation coefficients for the 1940 to 1980 time period. This fit included a full covariance analysis. The projected covariances were part of the a priori model for each epoch. An uncertainty model was adopted which included estimates of the effects of crustal and core fields not represented by the model. Differences between model coefficients midway in time between model epochs were compared to estimated coefficient uncertainties. Coefficient differences were within the estimated uncertainties, confirming the uncertainty model. A test for 1945 indicated that a solution without observatory biases was equal to that with such biases, within the expected uncertainties. Differences between biases from year to year are within the bounds expected based on the predicted uncertainties. The resulting models, their secular variation and their expected uncertainties are discussed in some detail.

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Section: The Modelssupporting

confidence: 77%

Section: The Modelsmentioning

confidence: 99%