The Variability of Cloud Condensation Nuclei and Cloud Droplet Populations in Convective Clouds over the High Plains: How Often are Continental Clouds Continental? New CCN Observations

Daily observations of cloud condensation nuclei (CCN) concentrations active at 0.4% supersaturation were conducted at the surface near mid-day for 3 weeks in August, 2004, at Bowman, ND. Average concentrations of these CCN over ~30 minute-long sampling periods varied day-to-day from ~30 to ~200 cm^-3. Preliminary analysis of weather conditions and 3-day back-trajectories associated with these measurements suggests that air reaching Bowman after recent association (within prior two days) with precipitating clouds has generally lower CCN concentrations, while air that has not been recently associated with precipitation systems is more likely to have relatively higher CCN concentrations. Air from the west typically had the highest concentrations, while air from the north typically was the cleanest, other factors being equal.