Long-term heliomagnetic field variation based on cosmogenic ⁴⁴Ti in meteorites

Reconstructions of the heliospheric magnetic field (HMF) in the past centuries are mainly based on the analysis of sunspot activity, geomagnetic data or on measurement of cosmogenic radioisotopes stored in terrestrial reservoirs (tree rings and ice cores). There are, however, significant discrepancies among the results obtained by various techniques using different proxies of solar magnetic activity. In this work, new results obtained from a unique approach based on the measurement of the cosmogenic ⁴⁴Ti activity detected in meteorites are presented and compared with the most recent reconstructions of the near-Earth HMF strength. The very low level of ⁴⁴Ti activity in several meteorites fallen in the last 250 years was determined by using gamma-ray spectrometers (HPGe+NaI) located in the underground laboratory of Monte dei Cappuccini (INAF-OATo) in Torino, Italy. This approach, specifically designed to overcome the main problems affecting other methods, yields a powerful independent tool to reconstruct the long-term evolution of the HMF through the last two and a half centuries.