Manifestation of Elevated Convection within Wintertime Extratropical Cyclones during IMPACTS. Part II: Hydrometeor Vertical Motions within and Outside of Elevated Potentially Unstable Layers

Abstract This study uses airborne, vertical W-band radial velocity ( V r ) radar data from seven ER-2 flights during the Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) field campaign together with High-Resolution Rapid Refresh (HRRR) model initialization data to investigate hydrometeor vertical motions within elevated potentially unstable and stable layers in winter extratropical cyclones. Cohen’s D test ( C d ) is used to evaluate how distributions of V r vary with cyclone type and intensity, within stable and unstable layers, and with characteristics of elevated potential instability (EPI) described in Part I. In general, hydrometeor vertical motions rarely exceeded 2 m s −1 within stable and EPI layers. The V r distributions, including stable and EPI layers, varied more by cyclone intensity than cyclone type. The V r distributions shifted toward positive values and broadened in stronger cyclones. Surprisingly, V r distributions were similar in stable and EPI layers ( C d = 0.15). The hydrometeor vertical motions in stable layers were associated with orographically induced gravity waves, shear-induced turbulence, and cloud-top generating cells. In general, the distance from the low pressure center, region within the comma head, depth of EPI layers, and number of EPI layers had little influence on the V r distributions. The V r distributions varied most by base height of the EPI layer ( C d = 0.28–0.68) followed by EPI magnitude ( C d = 0.37–0.66) where the higher the layer base, the more positive the V r mode. The stronger the instability, the more negative the V r mode, likely due to riming within elevated convection. Significance Statement Snowfall within winter storms can disrupt everyday life, impacting transportation, schools, businesses, and power. Snowfall arises from different circulations in the atmosphere ranging from broadscale ascent of air to small-scale buoyant circulations associated with elevated potential instability (EPI) above frontal zones, gravity waves, and shear turbulence. This paper examines the magnitude of hydrometeor vertical motions ( V r ) within the comma head region of winter cyclones based on vertically pointing radar data collected during 2 years of flights during the NASA Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) field campaigns as it relates to EPI characteristics, cyclone type, and cyclone intensity. In general, V r rarely exceeded 2 m s −1 within stable and EPI layers. The V r distributions, including stable and EPI layers, varied more by cyclone intensity than cyclone type. The V r distributions shifted toward positive values and broadened in stronger cyclones. Enhanced V r in stable layers was associated with orographically induced gravity waves, shear-induced turbulence, and cloud-top generating cells. In general, the distance from the low pressure center, region within the comma head, depth of EPI layers, and number of EPI layers had little influence on the V r distributions.