Near Surface Winds from an enhanced Micro-Mesoscale Simulation System

The ability to simulate very local-scale meteorological fields using a coupled micro-mesoscale set of models has previously been reported. This capability now is extended to compute vertical structure in the surface layer for all terrains using wind profiles produced by our micro-alpha/beta scale code as driven by our meso-gamma scale code. The further computation of surface layer mean vertical wind profiles at each (or selected) grid point(s) permits the construct of additional horizontal mean wind fields near the surface about open and covered complex terrain. The coupled codes are initialized with the one degree meso-beta scale model output for western US. The meso-gamma scale forecast is centered on an area the size of a state with 2.5Km grid resolution. This output, at the center-point of the micro- alpha scale grid, is interpolated to the required standard upper air levels while the appropriate lowest level output at the surrounding 16 grid points is treated as surface data. These two sets of information become the input to the micro-alpha scale code. The surface data input is further processed for slope-enhanced, localized flow and the temperatures are adjusted for the elevation differences using the original lapse rate, forming the first guess surface analysis. Next, the micro-scale code is run with a 50m grid resolution to include the interactions with existing land cover and complex terrain. Finally, the profiles are generated by coupling the ambient logarithmic relationship to the canopy’s exponential relationship derived using the underlying land cover. The micro-beta scale results at the required particular level then are selected at each grid point. Examples are given of the wind field interacting with 50m computational cells of terrain slopes and dominant features containing either vegetation, structures, or other simple land covers. Wind speed and direction at levels near the surface vary notably throughout the domain.