Relationship of Snow Microphysics and Precipitation Generating to Vertical Motions in Snowbands and Generating Cells in Snowstorms

In this study, 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 is used to characterize and compare the microphysics in the updraft and downdraft regions.

The measurements were acquired from the NASA P3 aircraft, which was equipped with a full complement of particle probes, direct measurements of condensed water content, and thermodynamic and 3D wind measurements. P3 aircraft data within snowbands, generating cells, and peripheral regions from 14 flights are composited and used for the analysis. Temperatures sampled ranged between -27 and +1⁰C.

The data are partitioned by updrafts, with strong updrafts defined as >0.5 m/s, and strong downdrafts, <-0.5 m/s. This partitioning revealed notably higher precipitation mass concentrations in the updrafts than downdrafts, a result of particle growth and relative fallout within the updrafts, “compression”, and fallout within the downdrafts “expansion”, in the downdrafts. Many bulk microphysical properties are consequently affected. Fallout of the larger aggregates through the updrafts and into the melting layer result in some interesting and 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.