Electrification Within Wintertime Stratiform Regions Sampled During the 2020/2022 NASA IMPACTS Field Campaign

Two nor'easter events-sampled during the NASA Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) field campaign-were examined to characterize the microphysics in relation to the underlying electrification processes within wintertime stratiform regions. A theoretical model was developed to determine whether accretion or diffusion growth regimes were preferential during periods of greatest electrification. Model simulation with electrification parameterization was used to provide supplemental context to the physical processes of in-cloud microphysics and electrification. The strongest electric fields (i.e., similar to 80 V m(-1) at 20 km) during the 2020 NASA IMPACTS deployment was associated with large non-rimed ice crystals colliding with each other. During the 29-30 January 2022 science flight, the NASA P-3 microphysical probe data demonstrated that non-inductive charging was possible off the coastline of Cape Cod, Massachusetts. Later in the science flight, when the NASA P-3 and ER-2 were coordinating with each other, measured electric fields consistently were less than 8 V m(-1) and electrification was subdued owing to reduced concentrations of graupel and large ice hydrometeors. Altogether, the in-situ observations provide evidence for the non-riming collisional charging mechanism and demonstrates that graupel and supercooled liquid water may not be necessary for weak electrification within wintertime stratiform regions. Model output from simulation of both events suggested that the main synoptic snowbands were associated with elevated hydrometeor snow charge density and electric fields. Plain Language Summary Cloud particle probe data and numerical weather prediction output were examined to understand the potential electrification processes for two winter storms that impacted the Northeast region of the United States. During the 7 February 2020 event, the greatest observed electrification was associated with pristine ice crystals and large snowflakes in an environment with little to no liquid water and high collision rates between large ice crystals. Electrification was likely during the earlier stages of the 29-30 January 2022 event-via collisions of graupel and ice hydrometeors in the presence of supercooled liquid water-but became subdued later in the flight due to the reduced number of graupel and ice crystals within the cloud structure. The numerical weather prediction model output from the two events suggested that snow carries the most electrical charge in wintertime stratiform regions.