Resolving issues concerning Eskdalemuir geomagnetic hourly values

Macmillan, Susan; Clarke, Ellen

doi:10.5194/angeo-29-283-2011

Cited by 9 publications

(8 citation statements)

References 8 publications

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“…We conclude that there is no problem with the Potsdam data. Bearing in mind the Eskdalemuir data change discussed earlier Macmillan and Clarke, 2011) we believe the most likely explanation is that the diurnal variation in the EKT data at this time may have been smoothed or may even have been recorded less often than hourly and interpolated: either would have artificially raised the r UT values.…”

Section: Comparing and Combining Indicesmentioning

confidence: 99%

Reconstruction of geomagnetic activity and near-Earth interplanetary conditions over the past 167 yr – Part 1: A new geomagnetic data composite

et al. 2013

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Abstract. We present a new composite of geomagnetic activity which is designed to be as homogeneous in its construction as possible. This is done by only combining data that, by virtue of the locations of the source observatories used, have similar responses to solar wind and IMF (interplanetary magnetic field) variations. This will enable us (in Part 2, Lockwood et al., 2013a) to use the new index to reconstruct the interplanetary magnetic field, B, back to 1846 with a full analysis of errors. Allowance is made for the effects of secular change in the geomagnetic field. The composite uses interdiurnal variation data from Helsinki for 1845-1890 (inclusive) and 1893-1896 and from Eskdalemuir from 1911 to the present. The gaps are filled using data from the Potsdam (1891Potsdam ( -1892Potsdam ( and 1897Potsdam ( -1907 and the nearby Seddin observatories (1908)(1909)(1910) and intercalibration achieved using the Potsdam-Seddin sequence. The new index is termed IDV(1d) because it employs many of the principles of the IDV index derived by Svalgaard and Cliver (2010), inspired by the u index of Bartels (1932); however, we revert to using one-day (1d) means, as employed by Bartels, because the use of near-midnight values in IDV introduces contamination by the substorm current wedge auroral electrojet, giving noise and a dependence on solar wind speed that varies with latitude. The composite is compared with independent, early data from European-sector stations, Greenwich, St Petersburg, Parc St Maur, and Ekaterinburg, as well as the composite u index, compiled from 2-6 stations by Bartels, and the IDV index of Svalgaard and Cliver. Agreement is found to be extremely good in all cases, except two. Firstly, the Greenwich data are shown to have gradually degraded in quality until new instrumentation was installed in 1915. Secondly, we infer that the Bartels u index is increasingly unreliable before about 1886 and overestimates the solar cycle amplitude between 1872 and 1883 and this is amplified in the proxy data used before 1872. This is therefore also true of the IDV index which makes direct use of the u index values.

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Section: Comparing and Combining Indicesmentioning

confidence: 99%

Reconstruction of geomagnetic activity and near-Earth interplanetary conditions over the past 167 yr – Part 1: A new geomagnetic data composite

et al. 2013

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“…The fit to the Master Composite is nearly as close as for the full 24-hour coverage, because the two hours chosen are near the average times of maximum effect. There is small systematic discrepancy for ESK before 1932 due to a change of data reduction in 1932 (MacMillan and Clarke, 2011). Because such meta-information is rarely available, we generally make no attempt to correct for known and unknown minor changes.…”

Section: Normalization Of the Diurnal Range Rymentioning

confidence: 99%

Reconstruction of Solar Extreme Ultraviolet Flux 1740 – 2015

Svalgaard

2016

Sol Phys

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Solar Extreme Ultraviolet (EUV) radiation creates the conducting E-layer of the ionosphere, mainly by photo ionization of molecular Oxygen. Solar heating of the ionosphere creates thermal winds which by dynamo action induce an electric field driving an electric current having a magnetic effect observable on the ground, as was discovered by G. Graham in 1722. The current rises and sets with the Sun and thus causes a readily observable diurnal variation of the geomagnetic field, allowing us the deduce the conductivity and thus the EUV flux as far back as reliable magnetic data reach. Highquality data go back to the 'Magnetic Crusade' of the 1830s and less reliable, but still usable, data are available for portions of the hundred years before that. J.R. Wolf and, independently, J.-A. Gautier discovered the dependence of the diurnal variation on solar activity, and today we understand and can invert that relationship to construct a reliable record of the EUV flux from the geomagnetic record. We compare that to the F10.7 flux and the sunspot number, and find that the reconstructed EUV flux reproduces the F10.7 flux with great accuracy. On the other hand, it appears that the Relative Sunspot Number as currently defined is beginning to no longer be a faithful representation of solar magnetic activity, at least as measured by the EUV and related indices. The reconstruction suggests that the EUV flux reaches the same low (but non-zero) value at every sunspot minimum (possibly including Grand Minima), representing an invariant 'solar magnetic ground state'.

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“…For example, in developing the IHV index (Svalgaard et al, 2004;Svalgaard and Cliver, 2007) using data from many stations, Leif Svalgaard in 2004 noted in a letter to the data curators that there appeared to be an error in the early hourly mean data from the Eskdalemuir station, something also noted by Martini and Mursula (2006). From careful comparisons with data from nearby stations, this error was corrected by Macmillan and Clarke (2011). Another example was poor calibration of the horizontal force variometer at Helsinki for a 6-year interval noted by Svalgaard (2014), which was causing the horizontal H component to be too small; Lockwood et al (2014a) also found that correcting for this using data on the vertical Z component indeed brought the data in line with the observations from other stations, particularly at the nearby St. Petersburg station.…”

Section: Calibration and Checking Of Geomagnetic Datamentioning

confidence: 99%

Application of historic datasets to understanding open solar flux and the 20th-century grand solar maximum. 1. Geomagnetic, ionospheric, and sunspot observations

Lockwood

Owens

Barnard

et al. 2022

Front. Astron. Space Sci.

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We updated annual mean reconstructions of near-Earth interplanetary conditions and (signed) open solar flux FS for the past 186 years. Furthermore, we added observations for solar cycle 24 to refine regressions and improved allowance for orthogardenhose and folded (a.k.a., switchback) heliospheric flux from studies using strahl electrons. We also improved the allowance made for the annual mean gardenhose angle of the interplanetary magnetic field. We used both multiple regression with interplanetary magnetic field B and solar wind speed VSW and linear regression with the function BVSWn and demonstrated that the latter gives correlations that are not significantly lower than those given by the former. We conducted a number of tests of the geomagnetic indices used, of which by far the most important is that all four usable pairings of indices produce almost identical results for B, VSW, and FS. All reconstructions were given full 2σ uncertainties using a Monte Carlo technique that generates an ensemble of 1 million members for each pairing of indices. The long-term variations of near-Earth interplanetary field B and open solar flux FS were found to closely match those of the international sunspot numbers but VSW show a significantly different variation. This result explains why of the two peaks of 20th-century grand solar maximum, the range geomagnetic indices give a larger second peak, whereas the diurnal variation indices give a first peak that is larger, as it is for sunspots. We found that the increase in solar cycle averages of FS was between 2.46 × 1014 Wb in 1906 and 4.10 × 1014 Wb in 1949, the peak of the grand maximum, and hence, the rise in open flux was by a factor of 67%.

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Resolving issues concerning Eskdalemuir geomagnetic hourly values

Cited by 9 publications

References 8 publications

Reconstruction of geomagnetic activity and near-Earth interplanetary conditions over the past 167 yr – Part 1: A new geomagnetic data composite

Reconstruction of geomagnetic activity and near-Earth interplanetary conditions over the past 167 yr – Part 1: A new geomagnetic data composite

Reconstruction of Solar Extreme Ultraviolet Flux 1740 – 2015

Application of historic datasets to understanding open solar flux and the 20th-century grand solar maximum. 1. Geomagnetic, ionospheric, and sunspot observations

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