Ice nuclei measurement validation and application toward modeling ice formation in clouds

Ice nuclei measurements play an important role in developing, validating, and improving empirical and theoretical parameterizations of ice nucleation processes. These parameterizations can then be used with numerical models to evaluate the influence of ice nuclei on ice formation and precipitation processes in mixed-phase clouds. Growing databases of laboratory and aircraft data on ice nuclei concentrations and activation properties, as a function of source composition and atmospheric processing, now exist. Atmospheric measurements over several projects confirm that number concentrations of atmospheric ice nuclei are usually very low, but highly variable in space and time. We condense this database into concise parameterizations that describe the variability of IN number concentrations as a function of aerosol number concentrations and physicochemical properties. We validate the parameterizations, and measurements upon which they are built, against data from laboratory expansion cloud chamber experiments and against observations of ice crystal concentration in clouds for which secondary ice generation does not play a role. These results indicate that present day ice nuclei measurements often accurately predict ice crystal concentration in clouds, although caveats exist and much more research is needed. Applications and implications are also discussed via a global climate model simulation.