Volume-equivalent Particle Research Articles

Estimation of Liquid Fraction of Wet Snow by Using 2-D Video Disdrometer and S-Band Weather Radar

Wet snow may cause significant damage to humans and property, and thus, it is necessary to estimate the corresponding liquid fraction (FL). Consequently, the FL of wet snow was estimated using a novel technique; specifically, the particle shape irregularity (Ir) was estimated through the particle coordinate information obtained using 2-D video disdrometer (2DVD) measurements. Moreover, the possibility of quantitively estimating FL via Ir, based on the temperature (T), was examined. Eight snowfall cases from 2014 to 2016 were observed through a 2DVD installed in Jincheon, South Korea, to analyze the dominant properties of physical variables of snowflakes (i.e., the terminal velocity (VT), particle density (ρs), Ir, and FL) and the corresponding relationships according to the T ranges (−4.5 < T (°C) < 2.5) in which wet snow can occur. It was clarified that the volume-equivalent particle diameter (D)–FL and D–Ir relationships depended on T, and a relationship existed between Ir and FL. The analysis results were verified using the Yong-In Testbed (YIT) S-band weather radar and T-matrix scattering simulation. The D–FL relationship was implemented in the scattering simulation, and the results indicated that the simulated reflectivity (ZS) was highly correlated with the observed reflectivity (ZO) under all T classes. These features can provide a basis for radar analysis and quantitative snowfall estimation for wet snow with various FL values.

Inversion of extinction data for irregularly shaped particles

The retrieval of extinction data in the highly urbanized region of Bratislava city is analyzed for both, strictly non-spherical particles and volume equivalent particles. Two most typical situations are discussed in more details: the summer time dusty atmosphere consisting of strongly scattering particles with refractive index about 1.59, and winter time atmosphere with usual occurrence of ice-phase aerosols. The attention is paid to more frequent continental polar air mass, with 54% occurrence probability in the Bratislava region. The root-mean-square error of measured optical data varies from 4% to 8%. When processing extinction data it is shown that there are no significant differences between modal radii computed under assumption of randomly oriented irregularly shaped particles and for Mie equivalents. However, the differences can occur in case on non-randomly oriented particles. The modal radius of equally oriented particles in the ice cloud can be about two times larger than a modal radius of the system volume of volume identical spheres. Particle irregularity and the roughness of its surface eliminate the interference structure and ripple typical for monodisperse scattering patterns. As a consequence the subsidiary mode within size distribution function disappears. Such a mode usually occurs with Mie particles. Assuming spherical particles for the computation yields a narrower size distribution compared to assuming irregularly shaped particles.