On the correlation between ice water content and ice crystal size and its application to radiative transfer and general circulation models

We performed correlation analysis involving ice water content (IWC) and mean effective ice crystal size (De) intended for application to climate models. For this purpose, ice crystal size distributions obtained from in situ measurements conducted from numerous field campaigns in the tropics, midlatitude, and Arctic regions were used and we show that IWC and De are well-correlated in this regional division. Including temperature classification in midlatitude cases increases this correlation. We applied the correlation results to cloud radiative forcing calculations in terms of IWC, in which De is expressed as a baseline mean and deviation from uncertainty in small ice crystal measurements. The latter deviates from the mean by less than 2 W/m² in net radiative forcing. Using the correlation results, simulations from the UCLA GCM showed substantial regional deviations in OLR and precipitation patterns from assuming a constant De.