Publication Date:
2016-06-18
Description:
This is Part 2 of a study of the near-Earth heliospheric magnetic field strength, B, since 1750. Part 1 [ Owens et al ., 2016] 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 paleo-cosmic 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 SSN-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 three-year averages centred 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.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
