Impacts of Atmospheric Rivers on Snow Microphysics

Atmospheric rivers (ARs) are long and narrow corridors of enhanced horizontal water vapor transport that supply mid- and high-latitude regions with anomalously high precipitable water vapor. ARs are associated with enhanced precipitation and winds, but are relatively understudied in how they impact snow microphysics. To understand how ARs impact these processes, we evaluate snowfall events coincident with an AR and those events not coincident with an AR. We designate these as “AR snowfall events” and “non-AR snowfall events”, respectively. To identify AR snowfall events, we first utilize a MERRA-2 reanalysis-based AR detection algorithm that is specifically tuned to colder and drier regions. We apply this algorithm for two distinct sites: Marquette, Michigan and Hyytiälä, Finland. The AR events and non-AR events are then refined to only include events that coincide with snowfall at each site. We analyze and compare the AR snowfall events against the non-AR snowfall events using the instrument suites at each site. The instrument suites include vertically-profiling radars, scanning radars, and custom NASA video disdrometers that are used to evaluate snow microphysics. We find that AR snowfall is associated with a higher number concentration of and denser particles than non-AR snowfall. By leveraging multiple ground-based instruments, we are able to characterize the differences in snow microphysics between AR and non-AR snowfall, which have implications for retrievals of snowfall from ground-based and space-based instruments.