A new particle–by –particle hot plate technique for measurement of precipitation rate, snow density and visibility

The diameter, mass and density of individual falling snowflakes is being measured automatically in Salt Lake City, Utah using a new device called the  Differential Emissivity Imaging Disdrometer (DEID). Hydrometeor properties are obtained from the DEID using a temperature-controlled hotplate to melt and evaporate hydrometeors and a thermal camera based upon the large difference in thermal emissivity between water and the aluminum hotplate. The density of each particle is calculated from the initial effective diameter imaged by the thermal camera and the individual particle mass, by assuming conservation of energy for heat transfer from the plate to the melted droplet and measuring the time taken for evaporation. Simultaneously recorded Multi-Angle Snowflake Camera (MASC) imagery provides hydrometeor types. These data are revealing detailed structures of snowfall density suited for avalanche studies, atmospheric precipitation rate, snow water equivalent and visibility, and size, and the mass and density distributions of individual particles. Results are generally consistent with past studies by e.g. Marshall and Palmer, Marshall and Gunn and Locatelli and Hobbs. However, order one million particles can be collected in a single storm cycle, so the range of particle collected and the statistical validity of the analyses is providing new insights into the nature of frozen precipitation.