The purpose of this project is to develop and utilize unmanned aircraft systems (UAS) to obtain critical meteorological observations aloft in the rear flank region of supercell thunderstorms. This is a pilot project with the initial emphasis being on the system development and obtaining experience in utilizing such systems in severe storm environments. If the pilot development project is successful, the Principal Investigators intend to participate in the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX 2). The investigators will utilize the expertise in unmanned aircraft operations of the University of Colorado to develop a system that is sufficiently safe to obtain a Certificate of Authorization for operation from the Federal Aviation Administration. Observations will be used to evaluate specific hypotheses related to the baroclinic generation of vorticity at the rear of the supercell updraft, and subsequent reorientation of that vorticity into the observed counter-rotating low-level vortices. The cyclonic member of this pair appears often to be the antecedent tornadic vortex.
Intellectual Merit Supercell tornadogenesis is the result of a complex series of processes. Evidence suggests that the vorticity in a tornado originates as horizontal vorticity between the supercell updraft and a trailing rear flank downdraft (RFD). The RFD, in turn, appears to be partially the result of small-scale precipitation structures unique to supercells: the hook echo and/or a narrow descending reflectivity core. In some supercells, the vorticity generated between the major vertical drafts is drawn upward in the updraft, leading to arched vortex lines and associated counter-rotating vortices in the rear flank gust front convergence zone. Under certain conditions, that appear to be governed by the degree of negative buoyancy in the RFD, tornadogenesis can occur in the vicinity of the cyclonic member of the counter-rotating pair.
Broader Impacts An important goal of this work is that it will contribute to the development of a rapidly-deployable mesoscale and stormscale UAS sensing system. The system will be suitably designed to greatly reduce regulatory hurdles to its future deployment. Important knowledge will be gained on technical and regulatory issues that will allow future deployments of UAS for weather research.
Collected observations will improve understanding of RFD buoyancy and tornado cyclone genesis. This information may lead to improvements in the tornado warning process via the diagnosis of rear-flank precipitation morphology and hydrometeor structure using Doppler radars with dual-polarization diversity capability. Further, it is anticipated that RFD buoyancy can be estimated through knowledge of the low-level thermodynamic stratification. Eventually, it is likely that operational meteorologists can make much better discriminations between potentially tornadic and non-tornadic supercells.
