Examination of atmospheric waves associated with 13 March 2003 bow echo

The Oklahoma Mesonet was used to analyze the surface features associated with the 13 March 2003 bow echo system. Two wave-like features were identified with this system through spatial and temporal filtering. The first was a gravity wave, presumed to be generated by deep heating within the convective line, which moved at nearly 33 m s^-1. The exact nature of the second wave-like feature cannot be determined from surface observations alone; this wave appeared as a surge of the mesohigh ahead of the convective line prior to bowing development. Passage of the second wave was marked by a sharp pressure rise approximately 20 minutes prior to a temperature drop at affected mesonet stations.

An idealized simulation of this bow echo was run using the Cloud Model 1 (CM1) version 1.15. The 0000 UTC 13 March 2003 KOUN sounding was used to initialize the system. All of the observed surface features, including the mesohigh pressure surge, were well represented. A fast-moving gravity wave was generated, likely by deep convective heating during the initiation of the system. The speed of this wave, approximately 30 m s^-1, closely matched that of the first observed wave feature. A bore was also generated ahead of the convective system due to the system's cold pool impinging on a low-level stable atmospheric layer. The stable layer was topped by an unstable layer where the mean environmental flow was close to the wave speed of the bore, allowing for trapping of the wave energy. Additional modifications were made to the model environment to simulate nighttime cooling, and the effects of this cooling on the generated bore were explored. Heating and cooling profiles within both simulated systems were examined to determine methods of generation of the wave and bore. Further investigation on the effects of these wave features on the pre-storm environment was conducted.

A “real-data” simulation of the bow echo was also run using the Advanced Research Weather Research and Forecasting model (WRF-ARW) version 3.2. A fast-moving gravity wave was generated, but an atmospheric bore was not. Evaluation of the simulation environment shows that the stability structure was significantly different than that of the 0000 UTC KOUN sounding; specifically, the low-level stable layer was no longer present.