Compute Bulk Density of winter events based on 2DVD Measurements

Quantitative analysis of winter precipitation is a great challenge for radar meteorology because of the complexity of winter precipitations. The winter precipitation can include different types of ice crystal, graupel and different types of snowflake dependent on the environmental conditions. Each of these precipitation particles has very different micro-physical properties. The most fundamental micro-physical property of these precipitation particles is density because it not only affects the dielectric constant of precipitation but also the liquid-equivalent snow rate. It is fairly standard to measure the total volume of winter precipitation in certain time period by using any type of disdrometer, and is easy to measure the total mass by any type of snow gauge. However, it is difficult to measure the density (or the mass) particle by particle. Huang et al. (2010 and 2014) showed that the density of snowflake can be computed by using the single camera data of two-dimensional video disdrometer (2DVD) and applying to the Böhm equation (1989). The advantage of single camera data is to avoid the significant miss-matching problem. However Huang et al (2014) also mentioned that the single camera data is not commercially available and only gave very limited information about the measured particle (e.g. there is no contour information). In this paper we propose a new method which uses the actual contour data from 2DVD to compute the density of winter precipitation particles based on Böhm equation. The cases from BAECC Snowfall Experiment conducted in Hyytiälä, Finland, jointly between University of Helsinki (UH), ARM, Finnish Meteorological institute (FMI), CSU and NASA is used to demonstrate the performance of this method.