Toward High-resolution Multiscale Simulations of Flows in Heterogeneous Atmospheric Boundary Layers

Ever since large-eddy simulation (LES) methodology was developed to study turbulent flows in the atmosphere (Lilly, 1967; Deardorff, 1970), it has been extensively used for studies of flat plate atmospheric boundary layers under the assumption of horizontal homogeneity. Carefully designed LES of canonical atmospheric boundary layers have contributed significantly to development of better understanding of these flows and their parameterizations in large scale models. These simulations were often carried out using research codes specifically designed and developed for LES of horizontally homogeneous flows. Recent developments in numerical weather prediction models enable multiscale numerical simulations across a wide range of atmospheric scales of motion. Toward a goal of developing a comprehensive multiscale simulation capability for a wide range of applications we are utilizing nesting capability in the Weather Research and Forecasting model. However, achieving accurate multiscale simulations requires: extensive code validation under a range of atmospheric conditions, addressing the question of appropriate lower boundary condition, and development of turbulence models for the range of scales between mesoscales and boundary layer scales (Wyngaard, 2004). Therefore, we start by focusing on validation of nested LES of ABLs using the Weather Research and Forecasting model and present results of several test cases including: complex terrain, heterogeneous surface characteristics and transport and dispersion.