Relating the Effects of Heterogeneous Terrain on Boundary Layer Flow to the Evolution of Preconvection Environments Using Remote Profiler Datasets from PERiLS

Abstract Earth’s surface can influence the behavior of the atmosphere across a broad spectrum of spatial and temporal scales. The atmospheric boundary layer (ABL), which is in direct contact with the surface, is especially sensitive to the effects of terrain. The dynamic structure and behavior of the ABL can be locally influenced by relatively small-scale surface terrain features such as hills, ridges, and even vegetation. In some cases, the impacts of terrain on the ABL may be relevant to severe convective storms and their hazards. This could be of particular importance across the expansive heterogeneous landscape of the southeastern United States (SE-US), a region that is notoriously vulnerable to tornadoes. During the Propagation, Evolution, and Rotation in Linear Storms (PERiLS) field campaign, which sought to improve the understanding of tornadoes in the SE-US, an expansive observation network that included multiple ABL profiling systems was deployed across the region. One of these systems was deployed along a distinct terrain gradient that delineates the union of the Mississippi River delta and the Bluff Hills in western Mississippi, an area where a pronounced gradient in historical tornado activity exists. Observations of three-dimensional ABL flow at this location indicate the presence of terrain-induced modifications to the low-level wind field that translate to locally enhanced storm-relative helicity (SRH) along this terrain gradient. These observations, and inferences drawn from them, emphasize the need for further investigation into the possible role of local terrain gradients on processes relevant to convective-scale weather hazards such as tornadoes. Significance Statement The surface of Earth plays a fundamental role in modulating the structure and behavior of the atmosphere. While the impacts of prominent surface terrain features such as mountain ranges are generally well understood, the influence of comparatively subtle terrain is less clear. Observations collected during recent field research deployments indicate that localized terrain gradients can modify low-level winds in a way that may be relevant to tornadoes. These observations highlight the need for further investigation into the influence that local terrain features may have on severe convective storms and their hazards.