Near-Storm Environment Spatiotemporal Analysis of the Lowest 1-km of the Boundary Layer using High-Resolving Mobile Lidar and Radar from the TORUS Project

Storm-scale processes that affect mesocyclogenesis, maintenance, and tornado-likelihood are still not fully understood owing to the lack of knowledge of the boundary layer evolution in both near-storm and ambient environments. The majority of prior studies have used idealized simulations to make vast kinematic and thermodynamic generalizations of the lowest few hundreds of meters of the boundary layer, often theorized to be important to a supercell’s tornado potential. The scarcity of boundary layer observations, usually only twice per day at NWS radiosonde launch sites (hundreds of kilometers apart) or at best hourly launches during a field campaign, is a major pitfall in quantifying heterogeneities in wind shear and storm-relative helicity in severe weather environments. The Targeted Observation by Radars and UAS of Supercells (TORUS) field campaign allows for the first direct kinematic comparison of the high-resolving NSSL mobile Doppler lidar and Texas Tech University mobile Ka-band radars, and thus, the ability to quantify the lowest-level near-storm environment wind flow evolution at unprecedented space and time scales.

The main goals of this study are to (1) assess the accuracy of wind measurements between the Doppler lidar’s continuous scanning mode and Ka radars’ VAD wind profile, (2) quantify the spatiotemporal heterogeneity of shear and storm-relative helicity in the lowest kilometer of the boundary layer, and (3) comparing the observed boundary layer evolution between strongly tornadic, weakly tornadic, and nontornadic supercells. When many scatterers are present (i.e. insects, dust, ect.) and the instruments were collocated, wind profiles were fairly consistent especially when the supercell was < 50 km in range and in inflow air. When scatterers were sparse, Ka radar winds had similar wind magnitudes as lidar but presented discrepancies in wind direction. Thus, changes in the magnitude of shear and storm-relative helicity at individual 100-m slices were analyzed to distinguish which slice contributed more to the overall 0-1 km layer. All three supercells exhibited noticeable increases of shear in the 0-100 m slice and little relative increases in any other slice. Although the 0-1 km storm-relative helicity increased as the supercells approached, which 100-m slice contributed more differed significantly between each storm and usually was not always the 0-100 m slice, showing the importance of understanding other layers relative to the typical 0-100 m layer for tornado potential. In addition to the lidar and radar analysis, other objectives were explored, such as kinematic comparisons to launched radiosondes and examination of temporal near-storm environment buoyancy changes.