AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
The Potential Role of Bacteria Acting as Ice Nuclei - A Numerical Model Study
MAHER SAHYOUN, Ulrik Korsholm, Jens Sørensen, Niels Nielsen, Kai Finster, Ulrich Karlson, Tina Temkiv, Allan Gross, Danish Meteorological Institute & Aarhus University
Abstract Number: 67 Working Group: Bioaerosols: Characterization and Environmental Impact
Abstract Some species of bacteria, e.g. Pseudomonas syringae, have been found efficient in nucleating ice at high temperatures in laboratory tests. Bacterial residence time in the atmospheric boundary layer is on the order of several days. Hence, ice nucleation active (INA) bacteria may be involved in the formation of ice and precipitation in mixed phase clouds, and could influence the climate and weather. This impact of INA bacteria could be explained by the presence of protein aggregates on their outer surface membranes, which serve as active sites for ice formation. In this way, bacteria can mediate immersion freezing of super cooled water at temperatures as high as -2°C.
However, having a notable effect of the abundance of the INA bacteria on global atmospheric scales is still not well known and needs to be investigated as well as their actual role on cloud formation.
A parameterization of homogeneous and heterogeneous ice nucleation rate based on classical nucleation theory (CNT) has been developed to calculate the probability of ice formation as a function of time. This parameterization is used to make a sensitivity study to test the probability of ice formation using INA bacteria at different sizes. The theoretical study also includes the impact of INA bacteria on the heterogeneous formation of ice in clouds and a comparison of their impact with other types of aerosols, e.g. dust and soot.
The main purpose of this study is to examine the impact of bacteria on cloud ice formation using a 1-d version of the numerical weather forecast model HIRLAM (High Resolution Limited Area Model). This is done by implementing the probability parameterization in the 1-d cloud scheme STRACO (Soft TRAnsition Condensation) to carry out a sensitivity study of the potential impact of INA bacteria on ice and precipitation formation.