Characterizing the Radar and Microphysical Properties within the Dendritic Growth Zone of Winter Storms Sampled during the Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS)

Winter cyclones are ubiquitous producers of heavy precipitation over the northeastern United States. Vertical radar cross-sections of these storms often reveal vertical gradients in the radar reflectivity factor (Ze) in the -10˚C and -20˚C layer with a RH_w of at least 101.5% compared to other warmer and colder layers. Some studies attribute this radar signature to the presence of oblate ice particles such as dendrites and often label this signature within this temperature range and supersaturation as the “Dendritic Growth Zone” (DGZ). On 23 January 2023, a positive-tilted upper-level trough over Ohio and Ontario resulted in a deepening surface low over northern New England, producing snowfall at the surface over New Hampshire and Maine. This storm was sampled by two research aircraft as part of the Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) NASA field campaign. The remote sensing ER-2 aircraft sampled the storm with radars at multiple frequencies, lidar and microwave radiometers, while the in-situ P-3 aircraft made microphysical and environmental measurements within the storm. In this project, in-situ measurements from the P-3 of liquid and ice water content, number drop concentration, and particle size distributions within the DGZ are analyzed and related to the radar reflectivity measurements made by the ER-2 radars. Four different flight legs were conducted by the aircraft within the DGZ during the 23 January 2023 storm, with the P-3 sampling the clouds from the 4.2 km to the 5.2 km altitude range and from the -10˚C to -19˚C temperature range. It was found that an abundance of supercooled water was present and numerous rimed ice crystals and polycrystals were present with growth regimes that were not exclusively dendritic, including tabular and columnar growth. Vertical Ka- and Ku-band radar cross-sections sampled by radars onboard the ER-2 revealed the presence of distinct vertical gradients of radar reflectivity within fall streaks for all four legs, some of which extended at higher altitudes above the DGZ temperature range. This suggests that the enhancement of radar reflectivity may not strictly be attributed to dendrites observed within the -10˚C and -20˚C temperature range but instead due to mixed microphysics and riming. Statistical analysis of these microphysical parameters using data collected from flight legs in the DGZ temperature range during other storms sampled during IMPACTS will also be presented.