Near‐Earth heliospheric magnetic field intensity since 1750: 2. Cosmogenic radionuclide reconstructions. Issue 7 (14th July 2016)

• Record Type: Journal Article
• Authors: Owens, M. J.; Cliver, E.; McCracken, K. G.; Beer, J.; Barnard, L.; Lockwood, M.; Rouillard, A.; Passos, D.; Riley, P.; Usoskin, I.; Wang, Y.‐M.
• Is Part Of: Journal of geophysical research. Volume 121:Issue 7(2016:Jul.)
• Page Start: 6064
• Page End: 6074
• Publication Date: 2016-07-14
• Subjects: galactic cosmic rays -- long‐term solar variability -- heliospheric magnetic field -- cosmogenic radionuclides; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/2016JA022550
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: 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 10 Be 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. Key Points: Reconstructions of the near‐Earth heliospheric magnetic field intensity, B, are compared back to 1750 Cosmogenic radionuclide reconstructions of B show reasonable agreement with sunspot‐ and geomagnetic‐based reconstructions Solar minimum conditions are particularly well matched, which may allow accurate reconstruction of B prior to 1610