Snow Settling in Atmospheric Turbulence

The objective of this contribution is to review more than 80 years of experimental measurements of the settling of snow particles and surrogates in natural and laboratory settings and suggest viable directions for future research. Under the broad category of frozen hydrometeors, snow particles are characterized by a variety of shapes and inertial properties that we broadly refer to as snow morphology attributes and depend on the micrometeorology of the air column, including temperature, relative humidity, wind speed, and turbulence. The uncertainty in the prediction of snow settling velocity is partly due to the significant variability in snow crystal shape, density, and drag properties, as well as the modulating effect of ambient turbulence, which has been observed to affect particle orientation and falling style and enhance or reduce the terminal velocity, as compared to quiescent flow conditions. Because of the complexity of finite-size, nonspherical particles’ interaction with turbulent flows at high Reynolds numbers, we stress the need for simultaneous flow and snow morphology measurements in the field and we review past and current experimental techniques and methodologies.