Examination of the Catch Efficiency of Snow Gauges based on the Observed Characteristics of Snow

Systematic errors in snowfall measurements are often observed due to the gauge-shield geometry. It is well documented that the catch efficiency of a gauge-shield configuration decreases with increasing wind speed, with a lot of scatter for a given wind speed. The cause of the scatter is currently thought to arise from the variability in the characteristics of snow, turbulence, and other unknown factors. This study will examine the variability of snow characteristics at the Marshall Field site near Boulder, Colorado during the SPICE WMO solid precipitation experiment using a variety of instruments including a Thies optical particle probe and weighing snow gauges for the period 2013-2015. A detailed analysis of the particle size distribution and terminal velocity will be conducted and related to the collection efficiency of single Alter shielded and unshielded snow gauges. Including unshielded gauges is important as one of the reference gauge configurations for SPICE is a single Alter and unshielded GEONOR or OTT Pluvio2 gauge. This study contributes to improve our understanding of the relationship between the type of snow and the automatic measurement of solid precipitation.