Relationship of Snow Microphysics and Precipitation Generation to Vertical Motions in Extratropical Cyclones: Results from IMPACTS

Abstract This study analyzes in situ aircraft microphysical measurements in deep snow-producing clouds during the Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) field programs in winter 2020, 2022, and 2023 to characterize and compare the microphysics in the updraft and downdraft regions. Measurements were acquired from the NASA P-3 aircraft equipped with a full complement of particle probes and instruments for direct measurements of condensed water content and thermodynamic and 3D wind measurements. We identified the P-3 aircraft flight days collected within snowbands, generating cells, and peripheral regions from 14 flights. These are composited and used for the analysis. Temperatures sampled ranged between −27° and +1°C. The data are partitioned by air vertical velocity, with strong updrafts defined as >0.5 m s −1 , very strong updrafts as >1 m s −1 , and strong downdrafts as <−0.5 m s −1 . This partitioning revealed precipitation mass concentrations that were 2x higher in the strong updrafts and 3x higher in the very strong updrafts than in the downdrafts, a result of particle growth and relative fallout within the updrafts. Total particle concentrations at the concentrations > 1 mm were about the same in each region. However, fallout of the larger aggregates through the updrafts at temperatures > −5°C and into the melting layer results in previously unreported shedding and lofting of the shed particles in the updrafts to subfreezing temperatures. This observation is supported by the overflying NASA ER-2 Doppler radar measurements. Significance Statement This study uses data from 3 years of wintertime field programs during the Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) field program. New insights are gained into differences in the properties of the updraft and downdraft regions and the lofting of drops created from melting snow aggregates that are lofted back by updrafts to subfreezing temperatures.