Time-frequency vortex characterization in large-scale experimental downbursts

Thunderstorms are severe atmospheric events with dramatic impacts on the Earth's surface. Among their various effects, downburst winds are especially significant, comprising a descending cold downdraft from the thunderstorm cloud and a horizontal outflow upon ground impact. The primary vortex dominates this flow in both stages, producing the highest near-ground velocities and forces. Due to the spatial and temporal transience of downbursts, experimental replication in specialized laboratories is essential for accurately investigating their dynamics. While traditional velocity measurements with Cobra probes offer high temporal resolution and a good spatial depiction of storm evolution through strategic instrument positioning and experimental repetitions, they often lack insights into the geometric and energetic characteristics of vortex structures and their correlation with recorded velocity signals. This paper addresses this gap through a time-frequency analysis of an extensive dataset of experimental downburst signals obtained at the WindEEE Dome simulator, Western University, Canada. The experimental configurations include isolated stationary downbursts, interactions with horizontal background wind within the atmospheric boundary layer, and effects of cloud motion on outflow patterns. The resulting asymmetry in horizontal outflow near the ground is captured through multiple Cobra probes positioned radially and azimuthally in the testing chamber. The continuous wavelet transform technique is applied to track the temporal evolution of energy content in downburst winds across the different simulated scenarios.