HR: 1340h
AN: A23C-0960    [Abstracts]
TI: Retrieval of Cloud-nucleating Aerosol in Arctic Stratus Clouds
AU: * Carrio, G G
EM: carrio@atmos.colostate.edu
AF: Colorado State University, Dept. of Atmospheric Science, Fort Collins, CO 80523-1371 United States
AU: Cotton, W R
EM: cotton@atmos.colostate.edu
AF: Colorado State University, Dept. of Atmospheric Science, Fort Collins, CO 80523-1371 United States
AU: Zupanski, D
EM: zupanski@cira.colostate.edu
AF: Cooperative Institute for Research in the Atmosphere, Colorado State University, Fort Collins, CO 80523-1375 United States
AB: This study analyzes the feasibility of retrieving cloud nucleating aerosol by assimilating real observations into a Large Eddy Simulation (LES) model. For this purpose, a Maximum Likelihood Ensemble Filter algorithm (MLEF, developed at CSU) was implemented into the LES version of the CSU Regional Atmospheric Modeling System (RAMS@CSU). The LES model is interfaced with the Los Alamos sea-ice model and its microphysical modules explicitly consider the nucleation of cloud condensation and ice forming nuclei (CCN and IFN). The MLEF algorithm calculates optimal estimates of the atmospheric state, model biases,and empirical parameters. It also calculates uncertainties of all estimates in terms of analysis and forecast error covariance. A well documented mixed-phase Arctic boundary layer (BL) cloud case (May 4 1998, SHEBA/FIRE) was chosen to perform the first series of assimilation experiments. Observed ice and water paths and/or downwelling radiative fluxes at the surface were periodically assimilated. After each assimilation cycle, a spin-up time is considered for each ensemble member in order to allow the development of an eddy distribution physically consistent with the new optimal model state. Simulations cover a period of 54 hours, although, no assimilation is performed during the first 8 hours. While all numerical simulations were initialized with low aerosol concentrations typical of a pristine Arctic environment, the LES model was successful in reproducing the observed presence of a moderately polluted air mass above the inversion. Results also suggest that assimilation of vertically-integrated quantities can enhance the capability of an LES model in simulating the microstructure of BL clouds. These preliminary results are encouraging, but further experimentation is necessary to develop a cloud nucleating aerosol retrieval method. Future efforts will directed towards finding the optimal configuration (e.g., observations to be assimilated, number of ensemble members and minimization iterations, assimilation frequency, etc), and also towards considering BL clouds cases in lower latitudes and using more complex observational operators.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 3307 Boundary layer processes
DE: 9315 Arctic region (0718, 4207)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005