Examination of debris loading effects on tornado dynamics using a Large-Eddy Simulation model and W-band mobile radar measurements

Tornadoes loft large amounts of debris that could affect its airflow through momentum exchange by drag forces. Past tornado simulations showed that sand-sized particles could significantly affect tornado dynamics (e.g., reducing near-surface wind speeds or inhibiting suction vortices) when large amounts of debris accumulate in the tornado's corner flow. While debris loading may affect vortex dynamics, observational evidence of debris loading effects is lacking because methods needed to estimate particle concentrations in tornadoes have not been developed (e.g., from radar measurements). In the present study, debris loading effects on tornado dynamics are examined for different particle types, including sand particles and wood boards, using a Large-Eddy Simulation (LES) model. To allow momentum exchange between the air and different particles, a two-way drag force coupling model is employed in the LES model. Using LES model output, simulated equivalent radar reflectivity factor and attenuation are calculated using Transmission (T) matrix calculations and advanced electromagnetic simulations. Methods for estimating maximum bounds on tornadic debris loading are presented, and suggestions for improving debris loading estimates using polarimetric radar at multiple frequencies will be discussed. Finally, estimates of debris loading from W-band mobile radar tornado cases will be presented.