Linking Aircraft, Radar, and Surface Observations to Understand Melting Layer Microphysics in Wintertime Stratiform Clouds

This study investigates microphysical processes within the melting layer (ML) of wintertime mixed-phase stratiform precipitation by integrating coordinated aircraft in situ measurements, ground-based radar, and disdrometer observations from the WINTRE-MIX field campaign near Trois-Rivières, Québec (Canada). The combined datasets provide a detailed view of vertical microphysical evolution during spiral ascent and descent of the NRC-Canada Convair-580 aircraft through the ML. Reflectivity and fall velocity profiles from the Micro Rain Radar and X-band airborne radar showed distinct bright band structures consistent with concurrent changes in temperature (T) and relative humidity (RH). In situ measurements indicated enhanced aggregation and riming just above the upper freezing height level ( ≈ 2 km), with maximum liquid water content and particle size near the middle ML where temperatures approached 2–3 °C. Below the lower freezing height level (0.5 km) rapid melting and breakup produced numerous smaller spherical ice pellets, consistent with surface disdrometer observations. Mass and reflectivity flux analyses indicated positive deviations from the steady state melting assumption, suggesting active microphysical processes including condensation and breakup. These findings provide new closure between radar and aircraft observations and offer critical insight into ML structure and processes that influence radar retrievals and numerical weather prediction model parameterizations.