Measurement and Analysis of the Microphysical Properties of Arctic Precipitation Showing Frequent Occurrence of Riming

Detailed ground‐based observations of snow are scarce in remote regions, such as the Arctic. Here, Multi‐Angle Snowflake Camera measurements of over 55,000 solid hydrometeors—obtained during a two‐year period from August 2016 to August 2018 at Oliktok Point, Alaska—are analyzed and compared to similar measurements from an earlier experiment at Alta, Utah. In general, distributions of hydrometeor fall speed, fall orientation, aspect ratio, flatness, and complexity (i.e., riming degree) were observed to be very similar between the two locations, except that Arctic hydrometeors tended to be smaller. In total, the slope parameter defining a negative exponential of the size distribution was approximately 50% steeper in the Arctic as at Alta. Sixty‐six percent of particles were observed to be rimed or moderately rimed with some suggestion that riming is favored by weak boundary layer stability. On average, the fall speed of rimed particles was not notably different from aggregates. However, graupel density and fall speed increase as cloud temperatures approach the melting point. Plain Language Summary Detailed measurements of snow are rare for remote regions like the Arctic. Here, we compare 2 years of automated photographic measurements of snow from Oliktok Point, Alaska, to prior measurements from the same camera system at a midlatitude site in Utah. Measurements of size, shape, fall speed, and fall orientation were quite similar although snowflakes tend to be substantially smaller at the Arctic site. There is also a surprisingly common occurrence of Arctic snow growing in the cloud by colliding with liquid droplets that exist in the clouds in relatively small amounts, despite being below the freezing point. While this type of snow, called graupel, is expected to have a relatively high mass density and therefore fall faster, it did not fall at significantly higher speeds compared to other types, but it did appear to increase in density as cloud temperatures approached the melting point of 0°C. Key Points Graupel density and fall speed decrease with the magnitude of supercooling Sparsely rimed aggregates form a larger portion of snow types with higher surface temperatures Hydrometeors observed in the Arctic are slightly smaller but otherwise remarkably similar to those at a midlatitude location