Idealized Baroclinic Wave Simulations and Field Observations to Explore Convective Multi-Bands Within the Comma Head of Winter Storms.
Abstract
Our understanding of convective organization within the comma head of extratropical cyclones is limited. The small-scale banding (or "multi-banding") and upscale growth mechanisms are difficult to observe and diagnose with sufficient resolution. Past studies have attributed these features mainly due conditional symmetric instability (CSI) in a frontogenetical environment, but our recent work has suggested they can occur in environments with little or no frontogenesis and weak instability. Thus, this study uses both idealized simulations and observations to answer questions such as: What are the environmental ingredients (e.g., instabilities, frontogenesis, shear) necessary for the development and longevity of these convective bands within extratropical cyclones? What role does potential vorticity generation and elongation (e.g., PV dipoles) have on the upscale growth of these bands? idealized runs are analyzed and compared with observations from the NASA IMPACTS (Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms) field experiment from 2020-2022 over the eastern U.S.
The idealized experiments use the moist baroclinic wave in WRF-ARW (v3.4.1). The parent domain has 100-km grid spacing and is 8000-by-8000 km in size. Inner 20-km, 4-km, and 0.8 km nests covering the comma-head region are added after 108 hours of simulation time. Between 117 h and 120 h, cells first develop east of the low within a region of 700-600-hPa potential instability and 900-800-hPa frontogenesis. The cells broaden into southwest-northeast bands parallel to the 600-500-hPa wind shear. By 138 h, the bands weaken as the instability is depleted. The northeastward elongation of the bands is associated with 500-hPa PV dipoles expanding down-shear from the convection. Diabatic processes redistribute the 600-500-hPa vertical shear to generate vertical relative vorticity and thus the dipoles. The vertical circulations from the dipoles may then promote additional upward motion, such that the convection in between them expands northeastward. These features and their evolution have been observed in cases during IMPACTS, such as the 16 January 2022 event over Georgia, and 7 February 2020 storm over the Northeast US, which will be highlighted using field data and additional WRF simulations.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.A32D1446L