Large-eddy simulation of a nocturnal stratocumulus-topped marine atmospheric boundary layer An uncertainty analysis

A large-eddy simulation (LES) model has been used to study a nocturnal stratocumulus topped marine atmospheric boundary layer. The main objectives of our study have been first to investigate the statistical significance of LES-derived data products. Second, to test the sensitivity of our LES results with respect to the representation of subgrid-scale mixing and microphysical processes, and third to evaluate and to quantify the parametric uncertainty arising from the incomplete knowledge of the environmental parameters that are required to specify the initial and boundary conditions of a particular case study. Model simulations were compared with observations obtained in solid stratocumulus during the third flight of the first ''Lagrangian'' experiment of the Atlantic stratocumulus transition experiment (ASTEX). Based on these simulations the following conclusions could be drawn: Resolution (50.50.25 m"3) and domain size (3.2.3.2.1.5 km"3) of the LES-calculations were adequate from a numerical point of view to represent the essential features of the stratocumulus topped boundary layer. However, the ensemble runs performed in our study to investigate the statistical significance of LES-derived data products demonstrate that the area-time averaging procedure for the second-order moments produces only a low degree of statistical reliability in the model results. This illustrates the necessity of having LES model results that are not only of adequate resolution but also of sufficiently large domain. (orig.)44 refs.Available from TIB Hannover: RR 1347(288) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman