No statistically significant effect of a short-term decrease in the nucleation rate on atmospheric aerosols
Observed correlations between short-term decreases in cosmic ray\nionisation and cloud and aerosol properties have been attributed to\nshort-term decreases in the ion-induced nucleation rate. We use a global\naerosol microphysics model to determine whether a 10 day reduction of\n15% in the nucleation rate could generate a statistically significant\nresponse in aerosol concentrations and optical properties. As an upper\nlimit to the possible effect of changes in ion-induced nucleation rate,\nwe perturb the total nucleation rate, which has been shown to generate\nparticle concentrations and nucleation events in reasonable agreement\nwith global observations. When measured against a known aerosol control\nstate, the model predicts a 0.15% decrease in global mean cloud\ncondensation nucleus concentration at the surface. However, taking into\naccount the variability in aerosol, no statistically significant\nresponse can be detected in concentrations of particles with diameters\nlarger than 10 nm, in cloud condensation nuclei with diameters larger\nthan 70 nm, or in the Angstrom exponent. The results suggest that the\nobserved correlation between short-term decreases in cosmic ray\nionisation and cloud and aerosol properties cannot be explained by\nassociated changes in the large-scale nucleation rate.