TY - JOUR

T1 - Reconstruction of geomagnetic activity and near-Earth interplanetary conditions over the past 167 yr – Part 3: Improved representation of solar cycle 11

AU - Lockwood, M.

AU - Nevanlinna, H.

AU - Vokhmyanin, M.

AU - Ponyavin, D.

AU - Sokolov, S.

AU - Barnard, L.

AU - Owens, M.J.

AU - Harrison, R.G.

AU - Rouillard, A.P.

AU - Scott, C.J.

PY - 2014

Y1 - 2014

N2 - Svalgaard (2014) has recently pointed out that the calibration of the Helsinki magnetic observatory's H component variometer was probably in error in published data for the years 1866–1874.5 and that this makes the interdiurnal variation index based on daily means, IDV(1d), (Lockwood et al., 2013a), and the interplanetary magnetic field strength derived from it (Lockwood et al., 2013b), too low around the peak of solar cycle 11. We use data from the modern Nurmijarvi station, relatively close to the site of the original Helsinki Observatory, to confirm a 30% underestimation in this interval and hence our results are fully consistent with the correction derived by Svalgaard. We show that the best method for recalibration uses the Helsinki Ak (H) and aa indices and is accurate to ±10%. This makes it preferable to recalibration using either the sunspot number or the diurnal range of geomagnetic activity which we find to be accurate to ±20%. In the case of Helsinki data during cycle 11, the two recalibration meth

AB - Svalgaard (2014) has recently pointed out that the calibration of the Helsinki magnetic observatory's H component variometer was probably in error in published data for the years 1866–1874.5 and that this makes the interdiurnal variation index based on daily means, IDV(1d), (Lockwood et al., 2013a), and the interplanetary magnetic field strength derived from it (Lockwood et al., 2013b), too low around the peak of solar cycle 11. We use data from the modern Nurmijarvi station, relatively close to the site of the original Helsinki Observatory, to confirm a 30% underestimation in this interval and hence our results are fully consistent with the correction derived by Svalgaard. We show that the best method for recalibration uses the Helsinki Ak (H) and aa indices and is accurate to ±10%. This makes it preferable to recalibration using either the sunspot number or the diurnal range of geomagnetic activity which we find to be accurate to ±20%. In the case of Helsinki data during cycle 11, the two recalibration meth

KW - Geomagnetism and palaeomagnetism (time variations, secular and long term

KW - instruments and technique) – interplanetary physics (interplanetary magnetic fields)

U2 - 10.5194/angeo-32-367-2014

DO - 10.5194/angeo-32-367-2014

M3 - Article

VL - 32

SP - 367

EP - 381

JO - Annales Geophysicae

JF - Annales Geophysicae

SN - 0992-7689

IS - 4

ER -