A Novel Technique for Automated Mass Measurements of Individual Snowflakes

Snowflake mass is a crucial parameter for the description of microwave scattering by a single snowflake or by a collection of many snowflakes. A realistic characterization of snowflake masses within snow clouds is therefore required for reliable retrievals of snow-cloud ice content and snowfall rate from atmospheric remote sensing observations. Thus far, snowflake masses have been determined from melted drop sizes of manually sampled snowflakes; and automated snowflake imaging has been used to approximate individual snowflake volumes and then relate the integrated snowflake volumes for a series of recorded snowflakes to corresponding measurements of the total snow water content. These methods have either relied on laborious manual sampling or derived descriptions of snowflake mass by averaging over many snowflakes. In contrast, the novel technique presented in this study allows automated mass measurements of individual snowflakes, based on the amount of energy required to evaporate a snowflake hitting a thin aluminum hotplate that is kept at a constant temperature above the boiling point. Here, snowflake mass is derived from the temperature drop at the hotplate that is associated with the evaporation of the snowflake. First measurements in the field indicate that the current hotplate sensor allows measurements of snowflake masses mf > 0.4 mg and a resolution of snowflake inter-arrival times between consecutive snowflake mass measurements of about 2 to 10 s depending on snowflake mass, when the influence of wind gusts on the hotplate is minimized through a wind fence. Planned applications of the hotplate sensor are to use the sensor (i) by itself for measurements of the statistical distribution of snowflake masses during snowstorms and (ii) in combination with high-resolution snowflake imaging techniques for coincident snowflake mass and shape measurements.