This award is under the International Postdoctoral Fellows Program, which enables U.S. scientists and engineers to conduct three to twelve months of research at foreign centers of proven excellence. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad. This award will support a twelve-month postdoctoral research visit by Dr. Steven T. Siems to work with Dr. Peter Jonas at UMIST in Manchester, UK. Dr. Siems and the atmospheric research group at UMIST have proposed adapting a large-eddy simulation model in an effort to better understand the direct impact cirrus clouds have on the Earth's radiation budget and the coupling between cloud dynamics and radiative exchange. A large-eddy simulation should prove to be effective given the microphysical variability found on scales of less than 1 km. This model is to include a representation of primary and secondary nucleation processes. It must allow for microphysical growth processes and dynamical structures to be present and interactive with the radioactive fluxes. Specifically, the model hopes to address issues concerning the occurrence of regions with high concentrations of small ice crystals. It is unclear as to whether these occurrences are more strongly influenced by fluctuations in the ice nucleus population or the internal dynamics of the cirrus. The model will also be used to address under the conditions under which regions containing liquid water can exist at temperatures below -30 degrees centigrade. The model may also be used to investigate the structure of contrails and how they differ from natural cirrus clouds. The award recommendation provides funds to cover international travel, a stipend for twelve months and a small allowance for in- country travel and attendance of a meeting.
