Surface-layer gust-structure derived from volume imaging lidar data and large eddy simulations

During the Lake-ICE experiment the University of Wisconsin Volume Imaging Lidar (UW-VIL) was located on the west shore of lake Michigan during cold air outbreaks. The lidar provided images of surface layer structure in the convective layer which developed over the windward side of the lake. In one of the lidar data acquisition modes, repeated horizontal scans at 5-m above the lake surface were recorded. This mode yielded images with 15 m spatial resolution and a scan repeat time of 25 seconds. The scans covered a 90 degree sector and produced useful data to a range of approximately 10 km. These images show cellular convection patterns in the steam fog. This paper examines the evolution and morphology of individual structures as they form near the shoreline and advect downwind.

As a part of our Lake-ICE research effort we are modeling the developing convective boundary with the University of Wisconsin Nonhydrostatic Modeling System (UW-NMS) using domain-sizes and grid-resolutions used in large-eddy simulations. The model was initialized with conditions to match those during the lidar observation. The model domain extended from 6 km inland of the shore line to 6 km offshore with 15-m resolution to match the lidar data. This allowed the formation of a realistic shear driven boundary layer at the upwind shore of the lake. Periodic boundary conditions were applied in the North-South direction. Inflow on the Western boundary was prescribed and radiative condition was used on the downwind boundary.

The model develops surface layer structure in the water vapor field which is very similar to that observed in the lidar images of the steam-fog. This allows us to use the LES eddy structure to infer the 3-dimensional eddy structure above the lidar scan-plane.