Near-Earth heliospheric magnetic field intensity since 1750: 2. Cosmogenic radionuclide reconstructions

M. J. Owens , E. Cliver , K. G. Mccracken , J. Beer , L. Barnard , M. Lockwood , A. Rouillard (1) , D. Passos , P. Riley , I. Usoskin , Y. -M. Wang

1 IRAP - Institut de recherche en astrophysique et planétologie

This is Part 2 of a study of the near-Earth heliospheric magnetic field strength, B, since 1750. Part 1 produced composite estimates of B from geomagnetic and sunspot data over the period 1750-2013. Sunspot-based reconstructions can be extended back to 1610, but the paleocosmic ray (PCR) record is the only data set capable of providing a record of solar activity on millennial timescales. The process for converting ¹⁰Be concentrations measured in ice cores to B is more complex than with geomagnetic and sunspot data, and the uncertainties in B derived from cosmogenic nuclides (~20% for any individual year) are much larger. Within this level of uncertainty, we find reasonable overall agreement between PCR-based B and the geomagnetic- and sunspot number-based series. This agreement was enhanced by excising low values in PCR-based B attributed to high-energy solar proton events. Other discordant intervals, with as yet unspecified causes remain included in our analysis. Comparison of 3 year averages centered on sunspot minimum yields reasonable agreement between the three estimates, providing a means to investigate the long-term changes in the heliospheric magnetic field into the past even without a means to remove solar proton events from the records.

Keywords: galactic cosmic rays; long-term solar variability; heliospheric magnetic field; cosmogenic radionuclides

Domains: Sciences of the Universe [physics]

M. J. Owens, E. Cliver, K. G. Mccracken, J. Beer, L. Barnard, et al.. Near-Earth heliospheric magnetic field intensity since 1750: 2. Cosmogenic radionuclide reconstructions. Journal of Geophysical Research: Space Physics, 2016, 121, pp.6064-6074. ⟨10.1002/2016JA022550⟩. ⟨insu-03669464⟩