Sensitivity of Simulated Turbulence to Terra Incognita: Implications for Linking Mesoscale and Microscale Models

Mesoscale simulations conducted with relatively fine horizontal grid spacing, on the order of a kilometer or less, can be contaminated by poorly resolved flow structures in the convective boundary layer. Using these grid spacings, originally dubbed Terra Incognita by Wyngaard (2004), for mesoscale simulations can lead to unrealistic variations in boundary-layer winds. In this study, we show it is critical to use a mesoscale model grid spacing larger than the depth of the convective boundary to ensure accurate simulations in the mesoscale domain. Using a grid spacing within Terra Incognita, however, is sometimes needed for model configurations that utilize coupled mesoscale and microscale (Large-Eddy Simulation—LES) domains. We will show that turbulent structures and flow characteristics within a sample LES domain are relatively insensitive to the grid spacing or turbulence model used in the parent domain. In addition, we will also show that the results are relatively insensitive to the size of the jump in grid spacing between the mesoscale and microscale domains.