An Equation for Estimating Westward Drift

James, R. W.

doi:10.5636/jgg.20.429

Cited by 7 publications

(4 citation statements)

References 4 publications

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“…D at a single location can hardly be taken as a measure of global westward drift. A more representative computation of westward drift can be obtained by using the spline representation of secular variation. Westward drift, ƒÓ, can be estimated at radius ƒÁ from (WHITHAM, 1958;NAGATA, 1962;JAMES, 1968JAMES, , 1970RICHMOND, 1969): 8). This change of slope has been discussed, e.g., by COURTILLOT et al (1978), DUCRUIX et al (1980, LE MOULL et al (1982), MALIN et al (1983), GUBBINS (1984) and MCLEOD (1985).…”

Section: Periodicities In the Secular Variationmentioning

confidence: 99%

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

Langel

Kerridge

Arraclough

et al. 1986

J. geomagn. geoelec

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The secular variation of the Earth's magnetic field is itself subject to temporal variations. We investigate these with the aid of the coefficients of a series of spherical harmonic models of secular variation deduced from data for the interval 1903-1982 from the worldwide network of magnetic observatories. For some studies it is convenient to approximate the time variation of the spherical harmonic coefficients with a smooth, continuous, function; for this we have used a spline fitting. The phenomena that are investigated include periodicities, discontinuities and correlation with the length of day. The numerical data we present will be of use for further investigations and for the synthesis of secular variation at any place and at any time within the interval of the data-they are not appropriate for temporal extrapolations.

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Section: Periodicities In the Secular Variationmentioning

confidence: 99%

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

Langel

Kerridge

Arraclough

et al. 1986

J. geomagn. geoelec

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“…First of all, we calculate intensity variations of the global geomagnetic non-dipole field by using eq (5). Like the calculation of the drift velocity, we choose the time span as 10 years, namely, τ = 10a, and compute the average intensity variation coefficient during each 10 years, and regard this average one as the coefficient of the midpoint during the decade.…”

Section: Intensity Variations Of the Non-dipole Field And Plane-tary-mentioning

confidence: 99%

“…The third method is whole-field velocity method. James [5] got the geomagnetic potential's drift velocities of 0.19 • /a, 0.18 • /a and 0.17 • /a, and the induction's (B) velocities of 0.16 • /a, 0.15 • /a and 0.14 • /a for epochs of 1945, 1960 and 1965. Using the same method, Richmond [6] got the drift velocities of 0.180 • /a and 0.133 • /a for the surface field and the core-mantle boundary field for 1965.…”

Section: Introductionmentioning

confidence: 99%

Drifts and Intensity Variations of the Geomagnetic Field

Wei¹,

Xu²

2001

Chinese J of Geophysics

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The Briggs' method of correlation analysis of moving random pattern is modified. The characteristics of the westward drift and intensity variations of the non-dipole geomagnetic field and 6 planetary-scale geomagnetic anomalies are studied. During 1900-2000, the non-dipole field drifted westward at an average speed of 0.15 • /a, and intensified by 29%. Six planetary-scale magnetic anomalies exhibited different characteristics in the drift. The African Anomaly (AF) drifts westward at an average speed of 0.26 • /a. The Australia Anomaly (AUS) drifts at an average speed of 0.23 • /a. The slowest drift occurs in the Eurasia Anomaly (EA) at an average speed of 0.09 • /a. As drifting westward, most anomalies drift northward slowly. During 1945During -1955, the anomalies EA, NAM, NAT in the northern hemisphere and AF near the equator changed its drift directions, from the westward to northwestward; a little later, the anomalies AUS and SAT in the southern hemisphere slowed down. In the 20 th century, the intensities of AUS, SAT, AF and EA, the largest in area and greatest in intensity anomalies, were increased, while the intensities of other two anomalies were decreased.

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“…Bullard (1950) calculated the drift velocities of spherical harmonics of the field and obtainedλ 1 1 = −0.003 • /a,λ 1 2 = −0.235 • /a,λ 2 2 = −0.363 • /a,λ 1 3 = 0.080 • /a,λ 2 3 = 0.080 • /a andλ 3 3 = −0.243 • /a (negative and positive values for westward and eastward drift, repectively). James (1968) get the drift velocities of 0.19 • /a, 0.18 • /a and 0.17 • /a for epochs of 1945, 1960 and 1965 respectively [4] . Using the same method, Richmond (1969) get the drift velocities of 0.180 • /a and 0.133 • /a of the surface field and the core-mantle boundary field for 1965 [5] .…”

Section: Introductionmentioning

confidence: 99%

Westward Drift of the Geomagnetic Anomaly in East Asia

Wei¹,

Xu²

2000

Chinese J of Geophysics

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The westward drift of East Asia geomagnetic anomaly is studied by using the technique of Correlation Analysis of Moving Random Pattern (CAMRAP) based on the International Geomagnetic Reference Field (IGRF) from 1900 to 1995. The drift velocity of the anomaly is calculated for X, Y and Z components, respectively. The drift velocity of Z component anomaly, which illustrates best the geomagnetic drift, is 0.07 • /a in average for the 100 years. This is distinctly slower than the global average westward drift of 0.2 • /a. At the same time the Z component anomaly slowly drifts northward at a speed of 0.02 • /a. Further analyses indicate three stages in the drift of East Asia geomagnetic anomaly. In the first stage from 1900 to 1930 the westward drift was fast, with an average speed of 0.10 • /a. Then, the drift changed to northwestward from 1930 to 1980. The westward speed was 0.07 • /a and northward speed was 0.04 • /a during this period. Finally, the drift almost stopped around 1980, and seems to change to eastwards.

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An Equation for Estimating Westward Drift

Cited by 7 publications

References 4 publications

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

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

Drifts and Intensity Variations of the Geomagnetic Field

Westward Drift of the Geomagnetic Anomaly in East Asia

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