Modeling theoretical radiative–dynamic response of tropospheric clouds to cosmic ray changes associated with Forbush Decrease events

Forbush Decrease (FD) effects on cloud composition and structure are under study and the results are still controversial. Time-scales are of paramount importance for supporting either a ‘microphysical hypothesis’, which hypothesizes a relation between FD and cloud microphysical parameters variability, or a different one. A most controversial question is related to the time delay between FD and cloud structure modification. The timescales of a radiative–dynamical mechanism, investigated through a simple model, are compatible with the observed variability with respect to cloud structure. Thus the delayed modification on cloud structure has to be put in relation with solar radiation variability, being coherent with the observed statistically significant Total Solar Irradiance (TSI), temperature and baric field variations, while not supporting the ‘microphysical hypothesis’.