New paper confirms the Sun was particularly active during the latter 20th century

A paper published today in Annales Geophysicae reconstructs solar geomagnetic activity over the past 167 years and shows a decrease of the interplanetary magnetic field [IMF, an indicator of solar activity] from 1846 to the first part of the 20th century, followed by increase of approximately 50% in the IMF over the twentieth century. The new paper corroborates author M. Lockwood's prior peer-reviewed publications demonstrating that the Sun was particularly active in the latter 20th century.

Fig. 7. Reconstructions of the near-Earth IMF, B, from geomagnetic data. The black line uses the new geomagnetic activity composite, IDV(1d) and the polynomial fit to B. The grey area surrounding this black line is the uncertainty band associated with using this polynomial fit derived using a Monte Carlo technique (see text for details). The red line shows the best reconstruction using a linear fit. The green line shows the SC10 reconstruction. Blue dots show the annual means of the observed IMF.

Although solar reconstructions and absolute sunspot numbers show a 20th century peak in the 1950's, the time-integral of accumulated solar energy shows a marked increase over the 20th century that, along with ocean oscillations, explains 90 to 96% of temperature observations over the past 163 years:

Ann. Geophys., 31, 1979-1992, 2013 www.ann-geophys.net/31/1979/2013/ doi:10.5194/angeo-31-1979-2013 Reconstruction of geomagnetic activity and near-Earth interplanetary conditions over the past 167 yr – Part 2: A new reconstruction of the interplanetary magnetic field

M. Lockwood¹, L. Barnard¹, H. Nevanlinna², M. J. Owens¹, R. G. Harrison¹, A. P. Rouillard³, and C. J. Davis^1
1Meteorology Department, University of Reading, Reading, Berkshire, UK
²Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, Finland
³Institut de Recherche en Astrophysique et Planétologie, 9 Ave. du Colonel Roche, BP 44 346, 31028 Toulouse Cedex 4, France
Abstract. We present a new reconstruction of the interplanetary magnetic field (IMF, B) for 1846–2012 with a full analysis of errors, based on the homogeneously constructed IDV(1d) composite of geomagnetic activity presented in Part 1 (Lockwood et al., 2013a). Analysis of the dependence of the commonly used geomagnetic indices on solar wind parameters is presented which helps explain why annual means of interdiurnal range data, such as the new composite, depend only on the IMF with only a very weak influence of the solar wind flow speed. The best results are obtained using a polynomial (rather than a linear) fit of the form B = χ · (IDV(1d) − β)^α with best-fit coefficients χ = 3.469, β = 1.393 nT, and α = 0.420. The results are contrasted with the reconstruction of the IMF since 1835 by Svalgaard and Cliver (2010).


The authors strongly object to the solar activity reconstruction of Svalgaard and Cliver, as well as Svalgaard's criticisms of their paper as a reviewer:

In reviewing this paper, L. Svalgaard (referee communication,
2013) has argued that the Helsinki H values, and
hence IDV(1d), are too low by about 30% between 1866
and 1873 (covering the peak of solar cycle 11) and argues
that this should be corrected. This raises a very important
discussion point. The argument for a correction is based on
comparing the range of the mean diurnal variations with the
group sunspot number. We strongly disagree, as a matter of
principle, that group sunspot number should be used to correct
the geomagnetic data in this way, for it will cause the geomagnetic
data to lose independence from the sunspot data
and the former will inevitably follow the latter. Indeed we
are extremely concerned that this sort of correction may have
been applied in the past to other geomagnetic data because,
although the correlation between average diurnal range and
group sunspot number is high (typically 0.9 for stations at the
latitudes used to generate the IDV(1d) index), we note that
agreement can be persistently poor (differences exceeding
50 %) in some solar cycles. In terms of this specific example,
one has to ask what could have changed in 1866 and then (exactly)
reversed in 1873, such that the error was only present
between these two dates? The Helsinki data were compiled
using the same instrumentation and procedures throughout.
The same error would have reduced the range Ak(H) variation
derived by Nevanlinna (2004) and Fig. 1 of that paper
shows that although it is a few percent lower than the linearly
regressed aa index in these years the difference is roughly
the same in magnitude as other years. As shown in Part 1,
IDV(1d) is considerably smaller than the Bartels u index in
this interval but Bartels himself considered u to be unsatisfactory
before 1872. Physically, Svalgaard argues that such
a correction is valid because the average diurnal variation

range is set by thermospheric winds driven by EUV heating
heating and that EUV mainly emanates from active regions and
hence the range of the diurnal variation depends only on the
group sunspot number. However, thermospheric winds, globally,
are also modulated by auroral energy deposition (which
has a UT variation, for example caused by dipole tilt effects,
introducing diurnal variation at a given location) and for the
higher latitude stations used in IDV(1d) (chosen to keep n
in BVn near zero) there is an influence of auroral currents

which will also have a diurnal variation. [Remainder p. 1989 in
the paper]


See also the 1st paper of this 3 part series by the same authors:

Ann. Geophys., 31, 1957-1977, 2013 www.ann-geophys.net/31/1957/2013/ doi:10.5194/angeo-31-1957-2013

Reconstruction of geomagnetic activity and near-Earth interplanetary conditions over the past 167 yr – Part 1: A new geomagnetic data composite
M. Lockwood¹, L. Barnard¹, H. Nevanlinna², M. J. Owens¹, R. G. Harrison¹, A. P. Rouillard³, and C. J. Davis^1
1Meteorology Department, University of Reading, Reading, Berkshire, UK
²Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, Finland
³Institut de Recherché en Astrophysique et Planétologie, 9 Ave. du Colonel Roche, BP 44 346, 31028 Toulouse Cedex 4, France
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 (1891–1892 and 1897–1907) and the nearby Seddin observatories (1908–1910) 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.

Prior posts on lead author M Lockwood