Measurement of snow settling dynamics using 3D particle tracking velocimetry

Understanding the dynamics of snow settling is important for improving our ability to predict ground snow accumulation, snow water equivalent, and surface thermal properties in a number of applications. Following our previous work using planar particle tracking velocimetry (PTV) to quantify snow settling dynamics in atmospheric surface layer (Nemes et al. JFM, 2017; Li et al., JFM, 2021), we present a further investigation of the problem with large-scale field 3D PTV system composed of four WiFi-synchronized cameras using drone-based calibration approach. The field deployment was conducted on April 17^th, 2022 at the field research station to capture 3D snow settling motions in a sampling volume of 4 m x 4 m x 6 m with 6.4 mm and 200 Hz spatial and temporal resolution, respectively. Our study provides a detailed geometric characterization of snow settling trajectories and reveals the highly variable and meandering trajectories of snow particles even under a low level of turbulence. The acceleration of individual snowflake yields a strong correlation with the curvature of particle trajectory and its statistics shows a strong anisotropic behavior under the influence of turbulence and snow particle morphology. Our Voronoi analysis shows evidence of 3D clustering of snow particles.