When You Get Bore-d: A Composite Analysis of the Impacts of Bore Passage on Boundary Layer Structure and Instability

While bores can frequently be found associated with nocturnal convection in the Great Plains, the relative paucity of soundings means that they tend to go underobserved, leading to many questions that remain unanswered about their structure, characteristics, and impact on subsequent convective development. Numerous studies have investigated individual bores, but these tend to focus on high-impact events that may not necessarily be representative of the phenomenon as a whole.

During PECAN, the presence of a dense vertically-pointing observation network coupled with the deployment of mobile facilities into the path of oncoming bores enabled the high-temporal resolution assessment of atmospheric thermodynamic and kinematic structure in both the pre-bore and post-bore environment. This allowed for the creation of a composite of over 20 bores that details typical changes forced by bores during their passage, while encompassing many more cases than typically found in previous bore observational studies. Key results show that bores tend to cause a decrease in the lifting condensation level (LCL) and the level of free convection (LFC). The mean convective available potential energy (CAPE) also, on average, tends to decrease with bore passage although the variability in these changes is greater with many cases indicating an increase in CAPE. Taken collectively, these results indicate that bores may increase the likelihood of convective initiation while at the same time decreasing the intensity of the convection that forms as compared to the pre-bore environment. Composite changes in surface pressure and lofting of near-surface air are consistent with earlier studies that focused on individual bores, giving high confidence in the representativeness of these results.