The long-term changes in solar meridional circulation as the cause for the long-term changes in the correlation between solar and geomagnetic activity

Since the beginning of the 20th century, the correlation in the 11-year solar cycle between the sunspot number and geomagnetic aa-index has been decreasing, while the lag between the two has been increasing. We show how this can be used as a proxy for the solar meridional circulation, and investigate the long-term changes in the meridional circulation and their role for solar activity and terrestrial climate