Fall velocity and axial ratio of snowflakes

摘要: In this work, we describe a method for optical snowflake measurements. The measurement area of the instrument consists two vertically offset measuring planes. Thus, side projections particles are taken. is capable to measure size, shape, and fall velocity individual ensembles particles. used in field campaigns collect data different crystal types riming degrees includes statistical evaluation presentation data. An example shows clear dependence particle speeds on riming. distribution depends density which increased due measurements include specification speed measured spread, e.g. 50% unrimed dendrites have velocity, more than 0.22 m/s from median value corresponding size class. Fall scatter increases vs. diameter range 0 mm 3.2 mm. Another axis ratio behaviour 1-dimensionally (e.g. needles) 2-dimensionally or plates) growing aggregates. 2-dimensional constant ratio, whereas show decreasing size. For both, 1-dimensional particles, decreases Finally, an effort made estimate Ar exposed flow relevant drag coefficient particle. Through comparison simulated dimensional view patterns, calculated areas can be obtained, because distributions estimated simulation.