Precipitation Growth Processes in the Comma Head Region of the 7 February 2020 Northeast Snowstorm: Results from IMPACTS

On 7 February 2020, precipitation within the comma head region of an extratropical cyclone was sampled remotely and in-situ by two research aircraft during the Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) field campaign, providing a vertical cross-section of microphysical observations and fine-scale radar measurements. The sampled region was stratified vertically by distinct temperature layers and horizontally into a stratiform region on the west side, and a region of elevated convection on the east side. In the stratiform region, precipitation formed near cloud top as polycrystalline crystals. No supercooled water was present. Polycrystalline habits occurred through the cloud depth, implying that the cloud top region was the primary source of particles. Total number concentration slightly decreased with depth, consistent with growth by vapor deposition and aggregation. In the convective region, new particle habits were observed within each temperature-defined layer along with detectable amounts of supercooled water, implying that ice particle formation occurred in several layers. Total number concentration decreased from cloud top to the -8°C level, consistent with particle aggregation. At temperatures >-8°C, ice particle concentrations in some regions increased to >100 L^-1, suggesting secondary ice production occurred at lower altitudes. Recent work also shows that cloud top phase was predominantly liquid within the convective region and predominantly ice within the stratiform region. WSR-88D reflectivity composites during the sampling period showed a weak, loosely organized banded feature. The increase in reflectivity associated with the easternmost band was consistent with the melting ice particles. A conceptual model of precipitation growth processes within the comma head will be presented.