What Voyager cosmic ray data in the outer heliosphere tells us about 10Be production in the Earth's polar atmosphere in the recent past

Abstract

Voyager measurements of the galactic proton and Helium nuclei spectra beyond the heliospheric termination shock and out to ∼110 AU seem to imply lower interstellar cosmic ray intensities of these nuclei than previously estimated. Using new interstellar spectra that are in much better agreement with these Voyager measurements we have calculated the production of 10Be in the Earth's polar atmosphere. This maximum possible 10Be production is only 1.47 ± 0.05 times the production occurring at recent times of minimum solar 11 year modulation between 1954 and 2009. This implies that the 10Be concentrations measured in polar ice cores at the times of the recent Spoerer and Maunder minima, which were between 1.6–2.0 times those measured recently at the times of minimum solar modulation, are most likely not solely related to changes in solar heliospheric modulation between these time periods, but other effects such as local and regional climate near the measuring sites may play a significant role in the differences in the relative 10Be concentration measurements at the two times.