Ice Nuclei and Ice Formation Processes in Tropical Cumulus Clouds

Colorado State University, Fort Collins CO

Investigators

Abstract

This award will provide researchers the opportunity to improve our understanding of the sources, physical and chemical nature, and number concentrations of atmospheric ice nuclei (IN). The measurements and modeling involved to be conducted are important in order to elucidate the roles of primary and secondary ice formation processes in determining microphysical composition and precipitation formation in cumulus clouds. The main aspect of this study is participation in the Ice in Clouds Experiment - Tropical Field Campaign (ICE-T). ICE-T is focused on improved understanding of the role of primary and secondary ice production in developing towering cumulus clouds through access to measurements to be collected during June-July 2011 by the NSF/NCAR C-130 aircraft. Research flights will be based out of St. Croix, in the U.S. Virgin Islands, with a target data collection region over the Western Tropical Atlantic and adjacent Caribbean Sea. Work supported under this award will provide IN measurements using the Colorado State University continuous flow diffusion chamber (CFDC) instrument, which is a annular flow diffusion chamber employing axial thermal gradients for real time ice nuclei measurements. The specific objectives are to perform airborne measurements aboard the C-130 to constrain the concentration of aerosols available to initiate ice by primary ice nucleation processes within the clouds being investigated, and to determine contributions of dust versus associated or unassociated biological aerosol toward ice formation at temperatures warmer than -20 degC. These investigators will then collaborate with other members of the ICE-T science team to analyze in-cloud ice formation processes a combination of via observational data and detailed numerical simulations. This support will also allow the investigative team to continue efforts to advance the technology for making atmospheric measurements of IN, including specialized implementations for ICE-T and participation in the proposed Instrument Development and Education in Airborne Sciences project. The intellectual merit of the award rests in expected improvements in understanding ice formation processes tropical cumuli, which are ubiquitous at near-equatorial latitudes, and in defining the role of different classes (inert vs. biological) of natural ice nuclei in triggering the initial formation of ice (and ultimately, precipitation) in such clouds. The broader impact of the research will include postdoctoral scientist training, collaborations with scientists in other institutions and disciplines, and enhancing U.S. research infrastructure. The obtained will be important for addressing such topics as aerosol-cloud-climate interactions and tropical storm formation. Additionally, a number of public outreach and educational activities are planned during the ICE-T field campaign.