Field and Laboratory Explorations of Marine Ice Nuclei

 

Authors

Paul J. DeMott — Colorado State University
Thomas C Hill — Colorado State University
Kimberly Prather — Scripps Institution of Oceanography
Christina S McCluskey — National Center for Atmospheric Research
Ryan Christopher Sullivan — Carnegie Mellon University
Ernie R. Lewis — Brookhaven National Laboratory
Sonia Kreidenweis — Colorado State University

Category

Ice Nucleation and Cloud Phase

Description

Measurements of the temperature spectrum of ice nucleating particle number concentrations in recent specialized laboratory sea spray studies at the NSF Center for Aerosol Impacts on Climate and the Environment at U.C. San Diego and in field campaigns at sites in the Northern Hemisphere will be discussed and compared with historical data from over global ocean regions. Online and offline methods are applied to measure the number concentrations of ice nuclei (IN) from realistically-generated laboratory sea spray particles (by wave generation or plunging water bubble production) and aerosols over marine regions. Measurements suggest that immersion freezing is the nearly exclusive mechanism by which such particles activate as ice nuclei, motivating online processing in this mode using a continuous flow diffusion chamber and comparison to offline processing of the freezing temperature spectra of collected aerosols dispersed into small liquid volumes. Typically, the number concentrations of IN from marine aerosols tend to be lower than are measured over land regions, are consistent with previous measurements made over oceans, and show general agreement between laboratory and atmospheric measurements. Nevertheless, sometimes strong variations in ice nuclei concentrations are found in accord with the seawater sampled and the biological processes occurring at the time of sampling. In the laboratory we have mimicked ocean situations dominated by growth of bacteria and growth of phytoplankton, observing IN increases in association with each case. Data from recent DOE-ARM MAGIC ship cruises will allow comparison of IN from oligotrhophic oceans versus other cruises that have crossed latitudes that include high chlorophyll-a oceanic regions. The nature of marine ice nucleating units of particles remains to be fully identified, and this will be required before informed quantitative predictions of these ice nuclei can be developed for modeling of impacts on mixed-phase clouds. Nevertheless, information will be presented on the general size range of these IN, inferences on organic versus inorganic speciation, and planned measurements to separate IN for mass spectral analysis. These measurements will inform future measurements proposed over the Southern Oceans.

Lead PI

Paul J. DeMott — Colorado State University