The near‐Earth magnetic field at 1980 determined from Magsat data

Langel, R. A.; Estes, R. H.

doi:10.1029/jb090ib03p02495

Cited by 202 publications

(107 citation statements)

References 20 publications

Supporting

Mentioning

102

Contrasting

Order By: Relevance

“…The mean Dst for the (filtered) POGS data is -10.0 nT, with a range of -46.0 nT to +28.3 nT. Thus (g1°,g11,s11) = (+20.1,-4.4,x.3) nT here can be described as being in reasonable agreement with Langel and Estes (1985b), although not strictly consistent with their observed Dst dependence of external coefficients. However, there may be longer term, periodic, variations in average external fields.…”

Section: External Field Coefficients and Main-field Modelssupporting

confidence: 76%

“…If we express the firstthree external field coefficients as a triplet (q 1°,q l 1 sl '),in a conventional notation, e.g., Langel and Estes (1985b), Langel (1987), we find that for the baseline model with added external (inclined) dipole, (q1°,g11,s11) = (+21.7,-6.8,-6.7) nT. In comparison the "best" POGS-based model, derived in Subsection 3.5 from a data set with a larger proportion of POGS data, results in (g1°,g11,s11) = (+20.1,-4.4,-4.3) nT.…”

Section: External Field Coefficients and Main-field Modelsmentioning

confidence: 99%

See 1 more Smart Citation

Geomagnetic Main-Field Modelling with POGS Satellite Data

Thomson

Macmillan

Barraclough

1997

J. geomagn. geoelec

View full text Add to dashboard Cite

Models of the geomagnetic main field of degree and order 13 are constructed for epoch 1992.5. These are based on combinations of (quiet-time, low activity) Polar Orbiting Geomagnetic Survey (POGS) total intensity data, and various near-surface, largely vector, measurements. We consider the significance in the fit of models to data of: (a) the spatial sampling interval; (b) the estimated ionospheric field corrections at POGS satellite altitude produced by Quinn et al. (1995); (c) the degree and order one external field coefficients; and (d) the relative proportions of POGS and near-surface data. At this degree and order it is found that: (a) the main-field model accuracy is relatively insensitive to the average sampling interval over a 15:1 range of intervals; (b) the most accurate models are those in which the estimated ionospheric field corrections are not included; (c) the external dipole term is of the order of +20 nT and hence has a marginal impact on model accuracy at the Earth's surface; and (d) a relatively high ratio, of order 4: 1, of POGS to surface data optimizes model accuracy at both POGS satellite altitude and ground level, although only a low ratio of POGS to surface data, of order 1:9, is required for high model accuracy at the Earth's surface alone. Overall, the most accurate main-field model produces spot values at the surface of the Earth with residual standard deviations between 96 nT and 120 nT, depending on component. An estimate of a typical "true", or absolute, model accuracy is also given, by comparing computed values, from a simplified model, with measured data from an independent near-surface data set. It is concluded that the absolute model accuracy at the Earth's surface is of the order of twice the accuracy of the model fit to its input data, again depending on component.

show abstract

Section: External Field Coefficients and Main-field Modelssupporting

confidence: 76%

Section: External Field Coefficients and Main-field Modelsmentioning

confidence: 99%

Geomagnetic Main-Field Modelling with POGS Satellite Data

Thomson

Macmillan

Barraclough

1997

J. geomagn. geoelec

View full text Add to dashboard Cite

show abstract

“…However, none of these indices assesses the absolute baseline of the quite-time magnetospheric field. Based on Magsat vector data the quiet-time magnetospheric field level was first estimated as 20 nT by Langel & Estes (1985a) and Langel & Estes (1985b). This first approximation was then specified using 9 yr of CHAMP data that revealed a stable quiet-time field of 13 nT with an additional variable part of up to 15 nT depending on the solar cycle phase .…”

Section: Introductionmentioning

confidence: 99%

An annual proxy for the geomagnetic signal of magnetospheric currents on Earth based on observatory data from 1900–2010

Pick

Korte

2017

Geophysical Journal International

View full text Add to dashboard Cite

S U M M A R YWe introduce the Annual Magnetospheric Currents index as long-term proxy for the geomagnetic signal of magnetospheric currents on Earth valid within the time span 1900-2010. Similar to the widely used disturbance storm time and 'Ring Current' indices, it is based on geomagnetic observatory data, but provides a realistic absolute level and uncertainty estimates. Crucial aspects to this end are the revision of observatory crustal biases as well as the implementation of a Bayesian inversion accounting for uncertainties in the main field estimate, both required for the index derivation. The observatory choice is based on a minimization of index variance during a reference period spanning 1960-2010. The new index is capable of correcting observatory time series from large-scale external signals in a user-friendly manner. At present the index is only available as annual mean values. An extension to hourly values for the same time span is in progress.

show abstract

“…A small, but significant difference in the amplitude of ring current magnetic signatures between LEO satellites and ground has been noticed in earlier years (e.g., Langel and Estes 1985b;Olsen 2002;Maus and Lühr 2005). Recently, Le et al (2011) compared C/NOFS satellite observations with the Dst-index for selected geomagnetic storms and found that the satellite observations have only about 80% amplitude of the signatures at ground.…”

Section: This Issue)mentioning

confidence: 99%