Development of UAV-Deployed Air-Launched Drifters (ALD) for Aboveground Thermodynamic Measurements in Supercells

Every year approximately one thousand tornadoes sweep across the United States, resulting in millions of dollars in damages and thousands of injuries. The most dangerous and destructive of these tornadoes come from supercell thunderstorms. Models and simulations provide valuable insight into the dynamics of supercells and tornadogenesis but without observational data it is difficult to determine their accuracy.

The rear-flank downdraft (RFD) is believed to be one of the regions within supercells that produces conditions necessary for tornadogenesis. However, strong downward winds characteristic of the RFD and its position behind the mesocyclone make the RFD a difficult region to access. Furthermore outflow winds behind the rear-flank gust front make it a particularly difficult region to attain direct measurements with balloon-borne sensors launched from the ground. A goal of the NSF National Robotics Initiative project “Severe-storm Targeted Observation and Robotic Monitoring” (STORM) is to develop new in-situ atmospheric sensing applications through targeted observations. STORM is a three-year collaboration of researchers from the University of Colorado Boulder (CU), University of Nebraska-Lincoln (UNL), and Texas Tech University (TTU). This paper describes the development and deployment of the Mistral small UAS (sUAS) with an integrated semi-Lagrangian drifter deployment system. The Mistral is the most recent in the line of sUAS, developed at the University of Colorado, for making meteorological measurements in supercells.

The Air-Launched Drifter (ALD) system is designed to deploy ALD balloons at an altitude above the supercell outflow, onto trajectories that entrain the balloons into the RFD or other regions of interest. The Mistral carries a helium tank to inflate and release up to four drifters during a single flight. Each drifter consists of small sensor board populated with a GPS receiver, pressure, temperature, and humidity sensors, and a communications radio. Telemetry and scientific data are collected from multiple fixed and mobile ground station receivers.

Results are presented from trajectory simulations as well as test flights done of the integrated semi-Lagrangian drifter deployment system. Furthermore, characterization tests of the microsondes, carried out during the 2018 STORM deployment and ISARRA 2018 flight week, are presented.