Sunday, 6 January 2013
Exhibit Hall 3 (Austin Convention Center)
Particular matter suspend in the atmosphere that provides a surface for water vapor to condense onto is termed Cloud Condensation Nuclei (CCN). CCN activation produces cloud droplets that can develop into rain. CCN number concentration is determined using a counter that pulls an air sample into a supersaturated environment and counts the number of droplets that form. CCN counters can be operated at the surface or deployed on aircraft to obtain measurements below cloud base. When using CCN measurements in scientific research, cloud base is typically the most desirable sampling location; however, the expense and difficulty of aircraft measurements limits their availability. The research objective is to determine under what meteorological conditions scientists can use surface based CCN measurements to infer cloud base CCN concentrations. Understanding when surface measurements can be used to predict cloud base CCN concentrations would allow long term, continuous, surface-based measurements to be used in many aerosol-cloud interaction studies. During the summer of 2010 and 2012, the University of North Dakota (UND) conducted sixteen aircraft flights that measured cloud base CCN concentrations with concurrent surface base CCN measurements in Grand Forks, North Dakota. Analysis of the summer 2010 cloud base and surface CCN concentrations show a good correlation (R2=0.42); however, the surface CCN concentration was more than 50% lower than the cloud base CCN concentration. UND calibrated on both aircraft and surface CCN counters using a Scanning Mobility Particle Sizer (SMPS) system. In addition to using the University of Wyoming CCN counters, the summer 2012 field program included the Droplet Measurement Technology CCN counter on both the aircraft and surface.
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