The Mechanisms for the Maintenance of Nocturnal Convective Systems

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Supported investigators will focus on improved detection and understanding of mechanisms leading to formation and maintenance of nocturnal deep convection (i.e., thunderstorms developing well after the cessation of maximum daytime heating) under conditions that include a low-level jet, stable boundary-layer stratification and elevated instability as signified by the largest Convectively Available Potential Energy (CAPE) being located near the altitude of this low-level jet wind maximum. This work is motivated by recent idealized studies that point to the potential importance of undular bores and internal gravity waves in maintaining nocturnal convection over the Great Plains region, as well as recent case-studies of by these investigators showing that a positive feedback may potentially exist between nocturnal convection, bores and the pre-convective environment. This work will take advantage of the operational rawinsonde network, composite radar data analyses, and advanced wind profiler data to conduct an in-depth study of the impact of the nocturnal weather systems on convective instability, and in so doing will seek to generalize prior descriptions of mechanisms that may serve to trap the vertical propagation of wave energy. Additional measurements will be obtained using an FM-CW (frequency modulated continuous wave) radar, scanning Doppler lidar and serial soundings. Lidar (light detection and ranging) data will allow identification of situations in which bore-lifted air is serving to feed convective updrafts. Non-hydrostatic numerical simulations will be conducted to advance understanding of observational results.The Intellectual Merit of this effort will derive from characterization of the complex interplay among nocturnal convection, undular bores and gravity waves with emphasis on assessment of cases where positive feedbacks among these features may be responsible for convective maintenance. Broader Impacts will include graduate student involvement in data collection and analysis, as well as anticipated linkages to NSF-supported REU (Research Experiences for Undergraduates) programs at National Weather Center and through integration of results into courses offered at the School of Meteorology. Ultimately, desirable impacts are also expected through improved ability to predict nocturnal thunderstorm development over the Great Plains and anticipate associated impacts on surface hydrology, energy production and agriculture, as well as related increases in public safety in situations involving hazardous nocturnal weather. This effort is also well paired with NOAA's stated goal to assess effectiveness of increasing dependence of storm-scale short-term forecasts on numerical models, as in the "Warn-on-Forecast" initiative. Findings may also be applicable in other continental regions beyond the U.S. Great Plains that exhibit a nocturnal maximum in thunderstorm occurrence.