Long-term solar activity reconstructions: direct test by cosmogenic 44Ti in meteorites

Aims.Long-term solar activity in the past is usually estimated from cosmogenic isotopes, 10Be or 14C, deposited in terrestrial archives such as ice cores and tree rings. A number of such reconstruction models have been proposed which differ from each other significantly. This approach suffers, however, from uncertainties due to the sensitivity of the data to several terrestrial processes. Here we propose a method to constrain these solar activity reconstructions using cosmogenic 44Ti activity in meteorites which is not affected by terrestrial processes. Methods.We test the veracity of recent solar activity reconstructions using the data on the activity of cosmogenic isotope 44Ti in meteorites which fell during the past 235 years, and provide an independent and direct measure of the cosmic ray flux near the Earth and allow decoupling of solar activity variations from terrestrial influences. Results.We demonstrate that the 44Ti data can distinguish between various reconstructions of past solar activity based on cosmogenic isotope data in terrestrial archives, allowing unrealistic models to be ruled out. We also show that a model based on the sunspot number record is consistent with the data on 44Ti activity in meteorites, thus confirming the validity of the method. In particular the 44Ti data confirm significant secular variations of the solar magnetic flux during the last century.