The influence of solar-modulated regional circulations and galactic cosmic rays on global cloud distribution.

The influence of solar forcing and Galactic Cosmic Rays (GCR) ionization on the global distribution of clouds is investigated using 42 years ERA-5 data (1979-2020). In the mid-latitudes over Eurasia, GCR and cloudiness are negatively correlated, which argues against the ionization theory of enhanced cloud droplet nucleation due to increased GCR during minima in the solar cycle. In the tropics, the solar cycle and cloudiness are positively correlated in regional Walker circulations below 2 km altitude.