Selection of a model of the Earth's magnetic field

Leonard, Robert S.

doi:10.1029/jz068i024p06437

Cited by 12 publications

(8 citation statements)

References 2 publications

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“…It Although the Vangb field gives comparable results in serving as a tool for analysis of the Vanguard 3 magnetic field data, its validity outside the regions of the data is even less than for Vanga. This fact was well illustrated when we attempted to find the Vangb conjugate point for Johnson Island to compare with those computed and observed by Leonard [1963]. The result is that for Vangb the magnetic equator passes nearly through Johnson Island and thus the conjugate point starting with an altitude of zero falls within 100 km!…”

supporting

confidence: 60%

“…The validity of these statements is amply illustrated by Leonard [1963] in connection with the Johnson Island tests. In his paper he shows that the observed auroral emission seen at a point conjugate to the bomb explosions could best be predicted by the set of 48 coefficients derived by Jensen and Cain [1962] and that the worst agreement resulted from using the Vanga coefficients.…”

mentioning

confidence: 96%

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Comments on the Vanguard 3 magnetic field data and analysis

Cain¹,

Hendricks²

1964

J. Geophys. Res.

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The principal results of the Vanguard 3 magnetic field experiment are summarized in a report and a paper [Cain et al., 1962 a, b]. Since some of the material presented in these documents has been used by several authors, it is worth while to clarify a few points and to report a modification indicated by a later analysis. The Vanguard 3 report gives a series of 63 spherical harmonic coefficients fitted to the data themselves by the iterative procedure of Jensen and Cain [1960] (reviewed by Heppner [1964]). This field, designated Vanga, used g• and h• • to n --m --7 and gave an rms deviation from the data of 21 7-The data selected for this fit were the 2797 observations given by Cain et al. [1962a] as L --0 (--best data), excluding four such observations with residuals (measured F-computed F) over 100 7. These observations were those recorded at Blossom Point, Maryland, on October 4, 1959, at Oh 47m 23s, Oh 47m 37s, 19h 50m 11s and 19h 50m 29s. In the Vanguard 3 report we

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supporting

confidence: 60%

mentioning

confidence: 96%

Comments on the Vanguard 3 magnetic field data and analysis

Cain¹,

Hendricks²

1964

J. Geophys. Res.

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“…Another independent s e t of information r e l a t i n g t o t h e way i n which v a r i o u s f i e l d models f i t a low l a t i t u d e f i e l d l i n e i s provided by Table 11 Distance R (km) between p o s i t i o n of observed a r t i f i c i a l a u r o r a (Leonard, 1963) Johnson I s l a n d bomb tests.…”

Section: (1963) F O R T H E Measurement I T Would Appear T H a T T H mentioning

confidence: 99%

An evaluation of the main geomagnetic field, 1940-1962

Cain¹,

Daniels²,

Hendricks³

et al. 1965

J. Geophys. Res.

125

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A set of 21,695 selected survey and observatory annual mean data available for the interval 1940–1963 is used to make a new determination of the geomagnetic field and its secular change. The field is given by a series of 63 spherical harmonics (gnm and hnm to n = m = 7) and 35 time derivatives (ġnm and to n = m = 5). Although it is inferred from these results that a better fit could be made with existing data if more coefficients were used, the improvement is substantial enough for us to recommend that the coefficients be used as a replacement for previously derived coefficients to evaluate the field at the current epoch. One refinement in the present determination is the use of an oblate earth in place of the spherical approximation. It is illustrated that this modification is necessary to obtain meaningful extrapolations above the earth's surface. The standard errors and confidence levels are given for the coefficients to show that almost all are well determined. It is shown that, when the field components computed using this new series are compared with several weighted selections of survey data, the rms deviations average only 210 γ (1955–1963), a value smaller than that obtained by other spherical harmonic series known to us.

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“…However, secular change has an even smaller effect on conjugate points in distorting the field. That is, although the (Leonard, 1963) and traces to 122-km altitude using field models indicated field as a whole appears to drift westward at rates estimated to be of the order of O. 'Z'/yr (Bullard et al, 1950), the shift of the relative locations of conjugate points is another order of magnitude less.…”

Section: Secular Changementioning

confidence: 97%

“…Such a close agreement in conjugate-point locations is typical of different points over the earth with different field models. Leonard (1963) reported an artificial aurora in the South Pacific that may provide a more sensitive test of conjugacy. In discussing the GSFC(4/64) model (Cain et al, 1965), we noted that the GSFC(4/64) model and the Leaton, Malin, and Evans (1965) model both show a difference of 27 km between observed and predicted positions.…”

Section: The Effect Of Improvements· In Field Modelsmentioning

confidence: 99%

The Role of the Main Geomagnetic Field in Locating Conjugate Points

Cain

1968

Radio Science

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A sample distribution of conjugate points is calculated from various models of the main geomagnetic field, evaluated at different epochs. A summary of the conclusions is: (1) For L < 4 the errors are of the order of a few tens of kilometers; (2) older models of the field such as the Finch‐Leaton give results within a few degrees of the latest more accurate models; (3) use of the eccentric dipole approximation gives errors that range from a few tens of kilometers at high latitude to several hundred kilometers near the equator; and (4) the secular change of conjugate‐point locations is very small, averaging 1 to 10 km/yr. Inclusion of Mead's boundary field for a trace from Macquarie Island to Alaska (L = S) shifts the conjugate only about 100 km. It is concluded that for L ⩾ 5 the field line passes through regions where the field intensity is weak enough to require that realistic estimates of the distortions due to plasma interactions be included in conjugate‐point determinations. (These estimates are not now available.)

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Selection of a model of the Earth's magnetic field

Cited by 12 publications

References 2 publications

Comments on the Vanguard 3 magnetic field data and analysis

Comments on the Vanguard 3 magnetic field data and analysis

An evaluation of the main geomagnetic field, 1940-1962

The Role of the Main Geomagnetic Field in Locating Conjugate Points

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