April 21, 2017 - 2:00 pm
April 21, 2017 - 3:00 pm
AddressNational Weather Center, 120 David L. Boren Blvd., Room 5600, Norman, OK 73072 View map
The Great Plains low-level jet during PECAN: observations, simulations, and ongoing analyses
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 including the OU-NSSL Collaborative Lower Atmospheric Boundary Layer Profiling System (CLAMPS). In this study, data sets from CLAMPS and fixed profiling sites FP2 (Greensburg) and FP3 (Ellis) during three PECAN NLLJ IOPs are interrogated to describe and contrast the evolution of NLLJs and study their role in modulating the structure of the NBL. In addition to observations, numerical simulations with the Weather Research and Forecasting (WRF) model are used in this study to further investigate the role of mesoscale processes in the formation and evolution of the NLLJ cases observed during PECAN. 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.
This seminar gives an overview of the selected PECAN NLLJ cases and presents an initial comparison of the WRF simulations with high-resolution observations from the CLAMPS system and FP sites. Analyses suggest that the simulated NLLJ typically forms earlier and is stronger than the observed counterpart early in the event, but weaker than the observed NLLJ later on. The WRF model predicts the height of the NLLJ maximum on a case-to-case basis; sometimes the height is captured quite well while other times the height is overestimated by the model. Potential temperature fields are well represented by the WRF model, as indicated by comparisons with the observed data. Finally, sudden variations in the boundary-layer winds seen in the observations on individual nights are well captured in the WRF simulations, and pulses of vertical motion often appear in the simulated flow fields very similarly to how they appear in the observed data. This seminar will also briefly discuss ongoing analyses using the validated WRF model output in tandem with the observed dataset. The first analysis topic focuses on the observed and simulated pulses of vertical motion mentioned in the model validation process. These features are further investigated through the lens of heterogeneous low-level jets as described by Gebauer (2017). The second analysis topic uses the validated WRF model dataset in tandem with observed datasets to investigate connections between the NLLJ and the NBL employing methods similar to those in Klein et al. (2015). As these analyses are still ongoing, this presentation intends to show progress and solicit feedback on the continuing work.