HR: 0800h
AN: A51E-0845    [Abstracts]
TI: Ice nucleation by cloud particle residues: Chemical compositions and inferences regarding ice initiation in clouds
AU: * DeMott, P J
EM: pdemott@lamar.colostate.edu
AF: Colorado State University, Department of Atmospheric Science, Fort Collins, CO 80523-1371 United States
AU: Twohy, C H
EM: twohy@coas.oregonstate.edu
AF: Oregon State University, College of Oceanic and Atmospheric Sciences, Corvallis, OR 97331-5503 United States
AU: Prenni, A J
EM: prenni@lamar.colostate.edu
AF: Colorado State University, Department of Atmospheric Science, Fort Collins, CO 80523-1371 United States
AU: Brooks, S D
EM: sbrooks@lamar.colostate.edu
AF: Colorado State University, Department of Atmospheric Science, Fort Collins, CO 80523-1371 United States
AU: Kreidenweis, S M
EM: sonia@chem.atmos.colostate.edu
AF: Colorado State University, Department of Atmospheric Science, Fort Collins, CO 80523-1371 United States
AU: Rogers, D C
AF: NCAR, ATD/RAF, Broomfield, CO 80021 United States
AU: Poellot, M
AF: University of North Dakota, Department of Atmospheric Sciences, Grand Forks, ND 58202-9006 United States
AB: Assessments of the impact of changing atmospheric aerosol particle concentrations and compositions on cold cloud processes depends on, 1) understanding the sources and behaviors of particles that serve as ice nuclei and, 2) demonstrating a direct connection between the ice nuclei and ice formation in clouds. Toward this end, this paper describes the combined use of two techniques to reveal the properties and influence of aerosol particles that act as heterogeneous ice nuclei (IN) in clouds. The role of IN in different cloud types is also assessed through comparison to cloud ice particle measurements. A counterflow virtual impactor was used for selectively sampling cloud particles during aircraft measurements of clouds. The concentrations, sizes and overall chemical compositions (by electron microscopy) of the evaporated residual aerosol particles were determined and these residual particles were then re-processed to determine their ice nucleating behavior for conditions of relevance to the clouds. A continuous flow ice-thermal diffusion chamber was used to process IN. Nucleated ice crystals were collected and IN residues were analyzed using electron microscopy. This method permitted comparing overall cloud particle residual chemistry to ice nuclei chemistry. The methodology is demonstrated through examples of studies in two cloud types. In the first case, we examine IN found in sub-tropical anvil cirrus clouds during the NASA CRYSTAL-FACE experiment. The variable contribution of heterogeneous IN to the overall concentrations of ice in anvil cirrus is emphasized, which was especially linked to the presence of Saharan dust. In no cases were heterogeneous ice nuclei the dominant contributor to ice present in anvils. We also examine the relation of IN to the presence of ice in mixed-phase clouds in the late Fall over the Northeast U.S. and Eastern Canada. Clear correlation between IN and ice in clouds was demonstrated on a few occasions. IN composition was dominated in both situations by markers for mineral dust particles, but with some apparent industrial contributions.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0320 Cloud physics and chemistry
DE: 0368 Troposphere--constituent transport and chemistry
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting