The Great Plains Low-Level Jet during PECAN: Observed and Simulated Characteristics

During the 2015 Plains Elevated Convection At Night (PECAN) field campaign, several nocturnal low-level jets (NLLJs) were observed with state-of-the-art integrated profiling systems. One such system, the Collaborative Lower Atmospheric Boundary Layer Profiling System (CLAMPS), was developed and operated during PECAN in collaboration between the University of Oklahoma and the National Severe Storms Laboratory. CLAMPS integrates a Doppler lidar, a microwave radiometer, an Atmospheric Emitted Radiance Interferometer (AERI), and a radiosonde system. Three other mobile platforms and six fixed platforms collected similar data in the PECAN domain. NLLJ intensive observation periods (IOPs) typically began before sunset at around 0 UTC and ended between 06-09 UTC, capturing in detail the evolution of the NLLJ and nocturnal boundary layer (NBL). In addition to observation data collected during PECAN, optimally configured Weather Research and Forecasting (WRF) model simulations have been used in the analysis. Previous work identified the optimal horizontal grid spacing, vertical grid spacing, and planetary boundary layer scheme for reproducing Great Plains NLLJs with the WRF model. Comparisons between the observed and WRF-simulated NLLJs allow for validation of the model configuration. Validated WRF model outputs then provide more detailed information about the observed NLLJ structure and evolution, as the increased spatial and temporal coverage of the numerical simulations permits a more thorough description of the events.

In this study, observations and simulations conducted un association with the PECAN NLLJ IOPs are used in conjunction to describe and contrast the evolution of NLLJs and study their role in modulating the structure of the NBL. A variety of interesting NLLJ phenomena that occurred during the IOPs were discover and explored. Instances of strong vertical motions were observed at various locations during NLLJ IOPs. The nature of these vertical motions has been investigated using both observations and simulations, which have also shed light on the heterogeneous character of the Great Plains NLLJs. Examples of such horizontal heterogeneities are demonstrated and their impacts on the nocturnal convection initiation are discussed. Linkages between the NLLJ and the NBL structure and stability have also been investigated.