Evaluation of Forecasts of Convectively Generated Bores and Bore Environments Using Observations from PECAN IOPs

An atmospheric bore is a quasi-permanent step-like increase in the depth of a temperature inversion, typically existing with superimposed undulations, resulting from stable partially blocked flow over an obstacle such as a convectively-generated density current. As a result of the ubiquity of observed bores in the Great Plains nocturnal convective environment, and their hypothesized role in the initiation and maintenance of nocturnal convection, the study of bores was one of the primary foci of the PECAN field experiment. In support of this focus, the present study investigates the ability to predict the speed and height of a bore observed during a PECAN Intensive Observing Period (IOP) at different times and locations, using the multi-scale GSI-based data assimilation and ensemble forecasting system. Observations collected during the PECAN IOP, particularly AERI retrievals of boundary layer thermodynamics and in situ observations from mobile sounding teams, provide truth data to evaluate the model bore simulations. It is found that the WSM6 microphysics scheme and MYJ or ACM2 boundary layer schemes predict the most realistic and accurate bore for this case, compared to several other WRF ARW physics schemes. However, pronounced biases in the bore strength and speed are still found in all model simulations. These results motivate ongoing work to improve the model simulations through tuning the model resolution and directly assimilating the PECAN IOP observations. Results on the sensitivity of bore simulations to horizontal and vertical grid spacing of both the forecast model and the data assimilation system will also be presented, along with preliminary work extending these experiments to 10 other bore IOPs.