Detection of snowfall occurrence during blowing snow events using photoelectric sensors

Abstract

There is a strong need to identify blowing snow events with and without concurrent falling snow and to estimate solid precipitation amounts in mountainous areas and polar regions. For these purposes, we first developed a method using the concomitant analysis of an anemometer and a drifting snow sensors (SPC-S7 and Wenglor/YH03PCT8-YH08PCT8). Photoelectric sensors, such as the SPC-S7 (Snow Particle Counter), specially designed for studying drifting snow, or a simpler photoelectric counter manufactured by Wenglor, were chosen because they had already been tested in previous studies for measuring solid precipitation. They were set up at Lac Blanc Pass, an experimental site dedicated to the study of drifting snow in the French Alps. The data set obtained was compared with the independent database of blowing snow events with or without falling snow collected at the same experimental site, i.e. data on the precipitation amount stemming from heated precipitation gauge and SAFRAN modeling output. The analysis of snow flux and mean diameter according to wind speed allowed us to separate blowing snow events with and without precipitation for moderate wind speed. To reduce the uncertainty at high wind speed, the SPC-S7 must be set up at least 4m above the snow surface. Similar preliminary results were obtained with the simpler Wenglor photoelectric counter, despite the minimum observable diameter being 200μm and the particle size distribution unavailable. These results must be confirmed by further experiments. The SPC-S7- estimated precipitation amount is in relatively good agreement with modeled precipitation given the many uncertainties due to the calculation hypotheses. Since the particle size distribution is not available for the simpler photoelectric counter and there are too many uncertainties and hypotheses in calculating solid precipitation, we concluded that the solid precipitation amount cannot be reliably estimated by the simple photoelectric counter.