This two-year effort will support collection and interpretation of fundamental aerosol and cloud microphysical measurements from instrumentation developed by Droplet Measurement Technology, Inc. (DMT) as operated aboard the NSF/NCAR C-130 aircraft during the ICE-T (the "Ice in Clouds Experiment-Tropical") field campaign. Unambiguous measurements of the mass of refractory black carbon (soot) particles to be made via a single-particle soot spectrometer (SP2), including residuals obtained from cloud droplet and ice crystal residues, will serve to describe how soot and dust particles are removed from the atmosphere as well as if (and perhaps how) these particles serve as efficient ice nuclei. Measurements of aerosol size distributions, shape and refractive index by DMT's aerosol particle spectrometer with depolarization (APSD) instrument will also be obtained.
The intellectual merit of this effort rests in the identification of those mechanisms leading to first-ice within comparatively shallow (and relatively ubiquitous) maritime convective clouds, which owing to their relatively short lifetimes may serve as a source of ambient ice that effectively seeds later developing cumulus clouds at relatively warm (ca. -10 degC) temperatures as well as through secondary ice production. Broader impacts of this research include expanded interactions and synergies between supported investigators active in instrument design with university-based researchers and students specializing in interpretation of large suites of data emerging from these and other instruments. Owing to one co-investigator's affiliation with the National Autonomous University of Mexico (UNAM), international collaborations and contributions to the advancement of science in a developing nation will also be encouraged.
In the ICE-T project, Droplet Measurement Technologies operated the Single Particle Soot Photometer (SP2) and the Aerosol Particle Spectrometer with Depolarization (APSD). The goal of the ICE-T program was to better define processes which lead to the formation of ice in tropical clouds. The measurement region was generally downwind of Puerto Rico. The measurements with the SP2 and the APSD were made both from an isokinetic inlet on the aircraft, sampling the pre-cloud aerosol and also using the Counterflow Virtual Impactor (CVI), which provides measurements of the cloud residual nuclei. The anthropogenic activity on Puerto Rico provides black carbon and soil dust as material for cloud nuclei. In addition the vegetation on Puerto Rico can provide pollen and other bio-aerosol particles which can serve as potential nuclei. The influence of Puerto Rico is clearly seen in the data as downwind of the island the concentrations of dust and black carbon particles are much higher. On Research flight #8 black carbon concentrations as high as 0.4 ug/m3 were observed directly downwind of Puerto Rico and the cocentration dropped off going away from the island. The APSD measurements identified iron oxide based material as a large portion of the supermicron aerosol material, indicating a crustal source. From the size distributions of the aerosol in clear air before cloud formation and the size distributions of the cloud residual material it much of the aerosol material appears to be effecient cloud nuclei.
