Large Eddy Simulations over Cape Cod in Support of the ARM Two-Column Aerosol Project

The Department of Energy's Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) began a one-year deployment on Cape Cod in July 2012 as part of the Two-Column Aerosol Project (TCAP). Among TCAP's many goals is the desire to evaluate the performance of regional models, particularly their microphysics and radiation parameterizations. To that end, the AMF suite of instruments, including microwave radiometers, Vaisala ceilometers, and cloud radars, is collecting observations of cloud properties at very high spatial and temporal resolutions. However, the optimal scanning strategy of the instrumentation varies based on characteristics of the boundary layer clouds. The coastal location of Cape Cod provides for a variety of boundary-layer cloud types and aerosol distributions, the latter of which are compounded by Cape Cod's position relative to the polluted Northeast Corridor; hence, the scanning strategy employed could have a large impact on the usefulness of the observations.

To assist this process, we are running the Weather Research and Forecasting (WRF) model at the LES scale over Cape Cod as an observing system simulation experiment (OSSE). In our approach, we define a total of seven domains. The outer four and inner three domains are each two-way nested, with a one-way “nestdown” step providing the interface between the mesoscale and LES configurations. The smallest domain uses a horizontal grid spacing of 50 m and 116 vertical levels. This provides enough resolution to examine different scanning strategies. In this work, we show preliminary results from the OSSE, including WRF output for a variety of boundary-layer cloud types, and discuss implications for the operation of the AMF.