HAPpy Hour Seminar: Microphysical growth processes within winter storms: insights from the IMPACTS field campaign

Abstract: The NASA IMPACTS (Investigation of Microphysics and Precipitation in Atlantic Coast-Threatening Snowstorms) field campaign, conducted in January and February of 2020, 2022, and 2023, focused on capturing the microphysical characteristics within and outside of mesoscale snowbands, which are typically associated with higher snowfall rates. This presentation synthesizes findings from three recent studies within the campaign investigating cloud microphysical processes.
On February 7, 2020, dual-aircraft observations provided a vertical cross-section of microphysical and radar measurements across the comma head region of an extratropical cyclone. The stratiform region, on the cold side of the comma head to the west, featured precipitation originating near cloud top as polycrystalline crystals with no supercooled water, consistent with growth by vapor deposition and aggregation. In contrast, the convective region to the east exhibited new particle habits and detectable supercooled water across multiple temperature layers, indicating ice particle formation in several distinct layers.
Additionally, an analysis of 26 research flights across the 2020, 2022, and 2023 deployments examined cloud-top phase relative to cloud-top temperature (CTT) using airborne lidar and Rapid Refresh data. The findings show that 19.2% of clouds sampled contained supercooled
liquid water at their tops, predominantly in clouds with CTTs warmer than -20°C, with occurrences as cold as -35°C.
Further, ongoing research investigates the linkage between microphysical properties and radar cross-sections in a shallow snowstorm over the Midwest on February 25, 2020. In situ data revealed that generating cell (GC) fall streaks precipitating into radar cross-sections increased
reflectivity and exhibited larger, high-aspect-ratio ice crystals. The southern end of the storm, characterized by the absence of GCs and presence of supercooled liquid water, showed signs of secondary ice production. GC plumes were observed to merging into regions of higher
reflectivity, potentially contributing to mesoscale snowband formation.

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