Improved understanding of bow echo evolution and long-lasting significantly severe thunderstorm winds

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Organized lines of thunderstorms, often known as squall lines or mesoscale convective systems, can produce large swaths of damaging winds. Two phenomena are particularly associated with high winds: bow echoes which are small segments embedded in a larger line that contain higher winds and seem to “bow” out ahead of the rest of the line, and derechos which are very long-lived lines which produce significant winds across a large area. This study will use fine resolution numerical modeling to investigate the processes that lead to bow echos and derechos. The high-impact nature of these events means that better understanding and the likelihood for better forecasting will have large dividends in terms of public safety and economic benefits. Additionally, students at various levels would be involved in the project, thereby training the next generation of scientists.The goal of this award is to improve understanding of the morphological evolution of mesoscale convective systems (MCSs), with an emphasis on bow echoes and the formation of significantly severe long-lasting wind associated with some of them (known as derecho events). The project will make use of the Weather Research and Forecasting (WRF) and Cloud Model 1 (CM1) numerical models to study various aspects of MCSs. In particular, the project will:• Examine the role of processes contributing to upscale growth in MCSs, particularly the strength of the temperature gradient at the leading edge of the cold pool, and contribution of gravity waves and direct lift at the leading edge of the cold pool, and their sensitivity to convection allowing model (CAM) grid spacing in simulations. • Examine the processes leading to bow echo formation, with emphasis on orientation of inflow, merger of lines with pre-existing cells, and presence of a boundary, and their sensitivity to CAM grid spacing.• Improve understanding of processes leading to long-lived significantly severe winds in MCSs, including the roles of features like the vertical position of dry air in the ambient environment, factors leading to intense mesoscale vortex formation in some cases, and whether such vortices are necessary for particularly strong, long-lived swaths of wind to form.• Study the impact of climate change on derecho events explored through the pseudo-global warming approach.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.