Understanding Ice Formation in the Atmosphere
Principal Investigator: Dan Cziczo
Co-Principal Investigator: Gourihar Kulkarni
This research area focuses on the development of new instruments to individually separate droplets and ice crystals from clouds, allowing the studies of their properties (e.g., size, shape, and the characteristics of the particle). Because the specific conditions responsible for cloud formation (e.g., relative humidity, temperature, and particle characteristics) cannot be adequately determined in the atmosphere, complementary instrumentation to mimic ice cloud formation under controlled conditions will be also developed. These new techniques will be designed to allow access to remote laboratory and aircraft so that the atmospheric locations with ice-containing clouds can be probed.
One project will build on the typical design of a counter-flow virtual impactor (CVI) to create the most advanced instrument of its kind available to the atmospheric science community. Another important aspect of this focus area is to develop a novel ice chamber to induce freezing at various temperature and supersaturation conditions to study ice nucleation. Coupling the ice chamber with the ice CVI and single particle mass spectrometer will provide much needed insight into particles that make good ice nuclei, as well as how they form. We expect the new findings to provide the scientific bases for parameterizations that will be incorporated into the models developed through this initiative. Below are some of the important results from this research focus area with the publication references.
Flow visualization within the counterflow virtual impactor instrument.
Flow visualization within the counterflow virtual impactor instrument. Computational fluid dynamics simulations showing detailed flow velocity streamlines in a counterflow virtual impactor instrument. Such detailed understanding helps to understand the instrument performance and build new instruments. Several design components of the instrument were commercialized. See Kulkarni et al. (2011). Enlarge Image
Performance and validation of ice chamber measurement conditions.
Validation of homogeneous freezing onset at -39 degrees C using the new ice chamber deployed at ~10,500 feet high mountain top facility in Colorado. Ambient particles activate, form droplets and freeze. The freezing efficiency increases above water saturation, and observed few hydrophobic particles require higher efficiency and freeze in the later period of the time. See Kulkarni et al. (2010), (presentations). Enlarge Image
Ice nucleation experiments showing soot as a poor ice nuclei.
Ice nucleation efficiency of uncoated and coated soot particles showing soot is a poor ice nuclei using the ice chamber developed at PNNL. The coated soot ice efficiency is not sensitive to the temperature and size. See Friedman, Kulkarni et al. (2011). (in review). Enlarge Image
Improving cloud model parameterizations using the laboratory ice chamber measurements.
Constraining the cloud model parameterizations using the ice chamber measurement data. The inset shows the PDF distribution derived from the experimental data. The distribution parameters for various ice nucleation measurements were derived and implemented into the parameterizations. Enlarge Image