Long-term variations in the open solar flux and possible links to Earth’s climate

Recent paleoclimate studies provide strong evidence for an association between cosmogenic isotope pro-duction and Earth’s climate throughout the holecene. These isotopes are generated by the bombardment of Earth’s atmosphere by galactic cosmic rays, the fluxes of which vary in approximately inverse proportion to the total open magnetic flux of the Sun. This paper discusses how results from the Ulysses spacecraft al-low us to quantify the open solar flux from observa-tions of near-Earth interplanetary space and to study its long-term variations using the homogeneous record of geomagnetic activity. A study of the results and of their accuracy is presented. The two proposed mecha-nisms that could lead to the open solar flux being a good proxy for solar-induced climate change are dis-cussed: the first is the modulation of the production of some types of cloud by the air ions produced by cos-mic rays; the second is a variation in the total or spec-tral solar irradiance, in association with changes in the open flux. Some implications for our understanding of anthropogenic climate change are discussed. Key words: Solar variability; climate change; helio-spheric field; solar irradiance; galactic cosmic rays; cosmogenic isotope