Supercooled Liquid Water at the Top of a Snow-Producing Nimbostratus Cloud and Its Association With Gravity Wave Breaking and Turbulence: An IMPACTS Case Study

Abstract

Supercooled liquid water (SLW) at the top of a snow-producing nimbostratus cloud was thoroughly characterized with remote-sensing and in situ measurements during the NASA Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) field campaign on 30 January 2022. With three coordinated flight legs, airborne downward-looking cloud radar and lidar and in situ microphysics and wind probes provided a comprehensive depiction of the cloud system over a one-hour period. NASA Cloud Physics Lidar (CPL) measurements suggest that the SLW layer was greater than several hundred meters thick and ∼100 km long within the sampling window. The in situ cloud probes measured a maximum liquid water content (LWC) of 0.58 g m⁻³. NASA Cloud Radar System (CRS) reflectivity and Doppler data revealed gravity waves within the nimbostratus below a strong temperature inversion that was caused by warm air advection near an occluded front in an extratropical cyclone. The enhanced CRS Doppler spectrum width indicated turbulence that was likely generated by gravity wave breaking while propagating upward. Analyses of the Brunt–Väisälä frequency and the Richardson number with NOAA High Resolution Rapid Refresh (HRRR) model supported the observed gravity wave activity. The eddy dissipation rate (EDR) was calculated from both the CRS spectrum width and the in situ wind measured by the Turbulent Air Motion Measurement Systems (TAMMS) to quantify the magnitudes of turbulence and to provide a promising intercomparison between the remote-sensing and in situ turbulence data. A moderate correlation between in situ EDR and LWC suggests that the turbulence likely contributed to the SLW cloud top.