ICE-L CCN Spectral Measurements

Affiliation(s)PIProject periodFunded by
DAS Hudson, James G 10/01/2006 - 09/30/2011 National Science Foundation

Project Description

Proposal Summary Desert Research Institute (DRI) cloud condensation nuclei (CCN) spectrometers would make aircraft measurements in the Ice in Clouds Experiment-Layer (ICE-L) field project, which is planned for March-April 2007 in the High Plains of Colorado. These measurements would include fine temporal, which for the aircraft means fine spatial (< 100 m) and supersaturation (S) resolution of the traditional Aitken CCN range (< 0.1 ?m dry soluble diameter) and the large nuclei range (0.1-1 ?m). This full range of S available only with the DRI instruments is necessary to ascertain relationships between CCN and ice nuclei (IN) measurements, which are the principal ICE-L aerosol measurement. But IN measurements are much less advanced than CCN measurements. The main goal of ICE-L is to determine whether cloud ice particle concentrations can be predicted from IN or other aerosol measurements. CCN are the principal 'other aerosol measurement' since it is well established that CCN spectra determine cloud droplet spectra, and since ice particle concentrations have often been found to be related to cloud droplet spectra. Since CCN concentrations are so much higher than IN concentrations they can be used to better outline many of the processes that relate aerosol-cloud interactions such as pollution, dust, entrainment and layering. This field project also offers numerous opportunities to produce further relationships between CCN spectra and cloud microphysics in significant cloud systems and environments distinctly different from most of those previously investigated. These relationships would include estimates of cloud S that determine the relative percentages of CCN that turn into cloud droplets. This helps to define CCN in various types of cloud systems. This is of fundamental importance to cloud physics and would considerably advance understanding of the indirect aerosol effect (IAE), which is the largest climate uncertainty. The wave clouds that are the primary focus of ICE-L provide unique opportunities to examine cloud formation in its purest form-with little entrainment of outside air and limited mixing of cloud parcels-and better measured vertical winds that bring about cloud S. Wave clouds should provide superior predictions of cloud droplet spectra based on CCN. The subsequent comparisons of these predictions with measurements of the cloud droplets may provide a more accurate estimate of a fundamental property of cloud droplet growth-the mass accommodation coefficient of water--that applies to all clouds. This would be fundamental to all cloud physics and would considerably advance IAE research. The prediction of ice particle concentrations from aerosol measurements (IN, CCN or others) that might result from ICE-L is so important because considerable changes in clouds usually ensue when ice forms. Namely this is usually the most efficient path to precipitation for which improved predictions would have enormous scientific and society impacts. A better understanding of ice initiation would also advance IAE research.