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

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 s²¹ 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 5 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 5 0.28–0.68) followed by EPI magnitude (C_d 5 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.