An ‘aerosol effect' detected but precipitation not affected

A 23-year record (1983/84-2005/06) of wintertime measurements at Storm Peak Laboratory (SPL) in the northern Colorado Rocky Mountains has shown, on average, condensation nucleus concentrations were directly related to cloud droplet concentrations and the droplet concentrations were inversely related to droplet mean diameters, evidence of an ‘aerosol effect'. With the removal of two outlying precipitation rate values, the droplet mean diameters were directly related to the precipitation rates; the mean diameters and precipitation rates are related through snow crystal riming. These results suggest aerosol concentrations can affect precipitation rates at SPL. However, there was no trend in either precipitation rates or in seasonal precipitation. Apparently, precipitation was governed more by meteorological factors than by aerosol concentrations.