Elizabeth Smith-December 8

Evolution of the nocturnal low-level jet and the nocturnal boundary layer during PECAN

High quality observations collected during the Plains Elevated Convection At Night (PECAN) field campaign allow investigation of the nocturnal boundary layer (NBL) and nocturnal low-level jets (NLLJs) common over the Great Plains. As presented in previous seminars, these observations can be used in tandem with optimally configured Weather Research and Forecasting (WRF) model simulations to offer a more extensive dataset for analysis. Observations and simulations are employed in the present study to describe and contrast the evolution of NLLJs and study their role in modulating the structure of the NBL. This work applies techniques developed by Bonin (2015), but expands upon previous work by carefully considering the dynamic nature of the NLLJ and NBL in these cases. NLLJs are classified as either weakly or strongly turbulent based on vertical velocity variance (s_w²) thresholds defined by Bonin (2015), and the classification is allowed to vary in time. The s_w² classification is compared to the more traditional classification of the NBL as weakly or strongly stable based on Richardson number considerations (e.g., Mahrt 2014). The s_w² classifications are then compared to synoptic setup for each event, the evolution of NLLJ height, and the evolution of NLLJ magnitude. The relationship between changing stability and the s_w² classification is evaluated. Finally, the relationship between the s_w² classification and the location of the NLLJ with respect to NBL inversions is explored.

Bonin, T. A., 2015: Nocturnal boundary layer and low-level jet characteristics under different turbulent regimes. Dissertation, University of Oklahoma, 169pp.

Mahrt L., 2014: Stably stratified atmospheric boundary layers. Annu. Rev. Fluid Mech., 46, 23-45.