Numerical Investigation of Damaging Wind Mechanisms within Bow Echoes

Lyndon State College, Lyndonville VT

Investigators

Abstract

Recent observational studies have documented the important role that low level (0-5 km AGL), small scale (1-10 km) "mesovortices" formed on the gust front of bow echoes play in producing both straight line and tornadic wind damage. It has been shown that mesovortices are capable of producing long, narrow straight-line wind damage swaths that have previously been attributed to a descending rear inflow jet. Further, mesovortices have been shown to produce the most intense damage within bow echoes. Yet, the genesis mechanism for these vortices is not well understood. The first objective of this research is, therefore, to examine the processes that create these vortices. A second objective is to better understand the dynamical processes that govern mesovortex strength. A spectrum of vortex strengths has been observed within bow echoes such that some are damaging while others are not. The objectives will be met by analyzing numerical simulations of an observed bow echo event where "mesovortices" produced the most intense straight-line wind damage along with tornadoes. The simulations will be produced by the Advanced Research Weather and Forecasting Model (ARW). Using a nested grid configuration, the ARW will have adequate spatial resolution to simulate the system-scale bow echo attributes along with sub-system scale mesovortices. A number of sensitivity experiments will be run to examine the model solution dependence on the initialization, environmental conditions, and various physics options that are available within the ARW. Intellectual Merit: The research objectives will further fundamental understanding of the important dynamical processes within bow echoes that produce damaging surface winds. The idea that mesovortices are capable of producing long, narrow swaths of straight-line wind damage challenges the long standing conceptual model that a descending rear inflow jet at the apex of the bow echo is responsible for much of the straight-line wind damage within bow echoes. Thus, it is important to understand the mesovortex genesis mechanism along with the dynamical processes that govern their strength in an effort to refine the conceptual model of how and where within bow echoes wind damage is produced. Broader Impacts The outcomes of the research may provide an important societal benefit by improving warnings for damaging surface winds produced by bow echoes. By understanding how mesovortices form, it may be possible to anticipate where and when damaging winds will be produced as the bow echo evolves. To minimize the false alarm rate, it will also be important to discriminate between the stronger damaging vortices and the weaker non damaging circulations. This research will expose undergraduate students to the research process. This research experience affords an experiential learning opportunity that is invaluable as they think about career options within the Atmospheric Sciences. They will also gain experience running a state-of-the-art mesoscale model. Having the ARW running at Lyndon State College will not only enhance the on campus research infrastructure but will also be used as a powerful teaching tool in many courses within the undergraduate curriculum.