Centennial changes in the solar wind speed and in the open solar flux

Abstract

[1] We use combinations of geomagnetic indices, based on both variation range and hourly means, to derive the solar wind flow speed, the interplanetary magnetic field strength at 1 AU and the total open solar flux between 1895 and the present. We analyze the effects of the regression procedure and geomagnetic indices used by adopting four analysis methods. These give a mean interplanetary magnetic field strength increase of 45.1 ± 4.5% between 1903 and 1956, associated with a 14.4 ± 0.7% rise in the solar wind speed. We use averaging timescales of 1 and 2 days to allow for the difference between the magnetic fluxes threading the coronal source surface and the heliocentric sphere at 1 AU. The largest uncertainties originate from the choice of regression procedure: the average of all eight estimates of the rise in open solar flux is 73.0 ± 5.0%, but the best procedure, giving the narrowest and most symmetric distribution of fit residuals, yields 87.3 ± 3.9%.

Total solar irradiance since 1996: is there a long-term variation unrelated to solar surface magnetic phenomena?

“…However, other proxies of solar magnetic activity like geomagnetic indices (e.g. Lockwood et al 1999;Rouillard et al 2007) and cosmogenic radionuclides (e.g. Beer et al 1998;Usoskin et al 2007;Steinhilber et al 2010) clearly show a long-term variation of the solar minima values.…”

Evidence of a long-term trend in total solar irradiance

“…This regression does not include the value of the proxy-based minimum in 1976, but its position close to the linear fit confirms the validity of this extrapolation over the 2.5 years with the proxy model. With the TSI-B R calibration and a reconstruction of the open magnetic field from geomagnetic indices (Lockwood et al 1999;Rouillard et al 2007;Svalgaard & Cliver 2007), TSI can be determined from B R ≈ 1.1 nT at the minimum of 1912/13 to be 1365.06 Wm −2 , which is 0.51 Wm −2 lower than during the minimum of 1986. During the MM, B R ≈ 0.7 nT (e.g.…”

“…A detailed reanalysis of the HF long-term behaviour by Fröhlich (2000Fröhlich ( , 2006 and comparison with ERBE data and the Kitt-Peak reconstruction (Wenzler et al 2006) confirm the need of the correction of HF. The results of another reconstruction (Krivova et al 2007) were used to "resolve" this issue by Scafetta & Willson (2009). Since this reconstruction was never designed to reproduce the details of the intra-cycle variability properly, these new arguments are only misleading and do not support the increase in TSI during cycle 22.…”

The solar magnetic field since 1700

“…The heliospheric open flux is extrapolated from the distribution of surface flux using the current sheet source surface (CSSS) model (Zhao & Hoeksema 1995a,b). The obtained open flux can be compared with reconstructions based upon the geomagnetic aa index (Russell 1975;Lockwood et al 1999;Svalgaard & Cliver 2005;Rouillard et al 2007) or upon cosmogenic radionuclide data such as the concentration of 10 Be in ice cores (Bard et al 1997;Caballero-Lopez et al 2004;McCracken 2007;Steinhilber et al 2010). …”