In Situ Observations of Ice Crystal Chain Aggregates in Winter Storms

Abstract Ice crystal chain aggregates—linear structures of conjoined monomer crystals—have previously been observed in strongly electrified deep convection, likely forming via electric‐field‐enhanced aggregation. The NASA Investigation of Microphysics and Precipitation for Atlantic Coast‐Threatening Snowstorms field campaign conducted aircraft‐based sampling of cold‐season storms using cloud probes. These measurements reveal chain aggregates in weakly electrified winter storms. Chain aggregates were identified in 28 of 34 research flights from 2020 to 2023 (∼10% of total P‐3 flight time), spanning −38°C to +2.5°C and 1.5–9.7 km. High‐resolution Cloud Particle Imager and Particle Habit Imaging and Polar Scattering imagery revealed sublimation signatures on chain aggregates, consistent across instruments. The widespread occurrence of chain aggregates in weakly electrified clouds suggests alternative formation pathways than electric‐field‐enhanced aggregation.