3.5 Solar activity reconstructions

Detailed computational models of cosmogenic isotope production in the atmosphere (e.g., Masarik and Beer, 1999Jump To The Next Citation Point) have opened up a new possibility for long-term solar-activity reconstruction (e.g., Beer, 2000). The first quantitative reconstructions of solar activity from cosmogenic proxy appeared in the early 2000s based on 10Be deposited in polar ice (Beer et al., 2003Jump To The Next Citation PointUsoskin et al., 2003cJump To The Next Citation Point).

Beer et al. (2003) reconstructed the modulation potential on a multi-millennial timescale using the model computations by Masarik and Beer (1999) and the 10Be data from the GISP2 core in Greenland. This result has been extended, even including the 14C data set, and presently covers the whole Holocene (Vonmoos et al., 2006Jump To The Next Citation PointSteinhilber et al., 2008).UpdateJump To The Next Update Information Usoskin et al. (2003cJump To The Next Citation Point) presented the reconstruction of sunspot activity over the last millennium, based on 10Be data from both Greenland and Antarctica, using a physics-based model described in detail in Usoskin et al. (2004Jump To The Next Citation Point). This result reproduces the four known grand minima of solar activity – Maunder, Spörer, Wolf and Oort minima (see Section 4.3). Later Solanki et al. (2004Jump To The Next Citation Point) reconstructed 10-year–averaged sunspot numbers from the 14C content in tree rings throughout the Holocene and estimated its uncertainties (see Figure 15View Image). This result was disputed by Muscheler et al. (2005Jump To The Next Citation Point), whose concurrent model, however, rested on an erroneous normalization, as argued in Solanki et al. (2005Jump To The Next Citation Point). The reconstruction of Solanki et al. (2004Jump To The Next Citation Point) has been recently updated by Usoskin et al. (2006aJump To The Next Citation Point), using a newer paleomagnetic reconstruction by Korte and Constable (2005Jump To The Next Citation Point), and was later slightly revised (Usoskin et al., 2007Jump To The Next Citation Point), considering an updated model of the solar open magnetic flux by Krivova et al. (2007). Reconstruction of the HMF from 10Be data has been performed by Caballero-Lopez and Moraal (2004), using a model of CR modulation in the heliosphere and a 10Be production model by Webber and Higbie (2003). Recently it was revised (McCracken, 2007) to present a detailed reconstruction of HMF intensity since 1428.

The obtained results are discussed in Section 4.

View Image

Figure 15: 10-year averaged sunspot numbers: Actual group sunspot numbers (thick grey line) and the reconstructions based on 10Be (thin curve, Usoskin et al., 2003cJump To The Next Citation Point) and on 14C (thick curve with error bars, Solanki et al., 2004Jump To The Next Citation Point). The horizontal dotted line depicts the high activity threshold.

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