Interplanetary magnetic field during the past 9300 years inferred from cosmogenic radionuclides

Abstract

We have reconstructed the interplanetary magnetic field (IMF), its radial component, and the open solar magnetic flux using the solar modulation potential derived from cosmogenic 10Be radionuclide data for a period covering the past 9300 years. Reconstructions using the assumption of both constant and variable solar wind speeds yielded closely similar results. During the Maunder Minimum, the strength of the IMF was approximately 2 nT compared to a mean value of 6.6 nT for the past 40 years, corresponding to an increase of the open solar magnetic flux of about 350%. We examine four cycles of the Hallstatt periodicity in the IMF with a mean period of ∼2250 years and an amplitude of ∼0.75 nT. Grand solar minima have largely occurred in clusters during the Hallstatt cycle minima around the years −5300, −3400, −1100, and +1500 A.D. The last cluster includes the Dalton, Maunder, and Spörer minima. We predict that the next such cluster will occur in about 1500 years. The long‐term IMF has varied between ∼2 nT and ∼8 nT and does not confirm a proposed floor (lower limit). There is a slowly changing long‐term trend of amplitude 1.5 nT, with a minimum around the year −4600 and a maximum around 0 A.D. that may be of solar origin but which also may be due to unknown long‐term changes in the atmospheric effects or geomagnetic field intensity.

A Remarkable Recent Transition in the Solar Dynamo

“…A Grand Minimum does not seem probable. Steinhilber et al (2009Steinhilber et al ( , 2010 have shown that such type minima occur only during negative phases of the Hallstatt period of solar activity and that statement was confirmed by de Jager and Duhau (2012). The Hallstatt cycle (Clilverd et al 2003(Clilverd et al , 2006Muscheler et al 2004) has a length of 2300 years, and it is, as observations show (cf.…”

“…also Fig. 13): During the negative phases of the Hallstatt periodicity of some 2000 years, Grand Minima cluster together (Steinhilber et al 2010). They do not occur during the positive phase.…”

The floor in the solar wind: status report

“…It makes the ∼50% drop in solar wind B M I N (measured above the floor) between the minima preceding cycles 23 and 24 comparable to the corresponding ∼45% drop in DM (Cliver & Ling, 2010). Finally, a floor at ∼2.8 nT accommodates most of the 10,000 year 10 Be-based reconstruction of B from Steinhilber et al (2010) except for several sharp dropouts where B goes to ∼0 nT (Fig. 3). 3.…”

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

“…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. Thus, maybe the postulated decrease in temperature is indirectly the result of solar magnetism.…”