Manifestation of Elevated Convection in Wintertime Extratropical Cyclones during IMPACTS
During January and February of 2020, 2022, and 2023, IMPACTS sampled wintertime extratropical cyclones (WTEC) and frontal systems. Past studies of WTECs east of the Rocky Mountains and IMPACTS case studies showed that elevated potential instability (EPI) occurs within the comma head when dry air descends above a moist airmass near the low-pressure center. However, the frequency, depth, strength, number of layers, and location of EPI along with the strength of vertical circulations resulting from EPI is not understood. This work overlays RAP equivalent potential temperature on X and W-band radar data from 19 WTECs sampled during IMPACTS. Each cyclone was categorized based on type and the strength to investigate how the characteristic of EPI varied between cyclones. We found that 74% of 1 km columns in the flight legs for 19 IOPs contained EPI. EPI occurred in all regions within the comma head with a median distance of ~360 km from the center of the WTEC. 70% of EPI was one layer and 26% was two layers with >1 layer of instability occurring closer to the center of the low. The magnitude of the strongest EPI was 8.3 K/km, with an average of 1 K/km, and the 95th percentile was 3 K/km. The median strength of EPI was independent of cyclone intensity and type; however, the cyclones with strength 1-2 mb/100 km and Miller Type B cyclones had the strongest outliers of EPI strength. In stable regions, vertical radial velocities were -4.5 to 1 ms-1. In layers containing EPI, the range was -7.5 to 6 ms-1 where vertical radial velocities increased as EPI strengthened. Therefore, EPI was common within IMPACTS WTECs and was correlated with enhanced vertical motions across all cyclone types and intensity.
