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- Title
The Impact of Offshore‐Propagating Squall Lines on Coastal‐Mountain Flows.
- Authors
Wu, Fan; Lombardo, Kelly
- Abstract
Dynamical physical processes associated with an onshore moving marine atmospheric boundary layer (MABL, i.e., sea breeze) over sloping terrain, sensitivity of these processes to MABL characteristics, and flow modifications induced by an offshore‐moving squall line are investigated using idealized simulations. The moving MABL gradually advances inland, exhibiting farther advancement and greater upslope wind speed for deeper and cooler MABLs. The local acceleration is primarily driven by a MABL‐generated perturbation pressure gradient force (PPGF). As the moving MABL air accumulates onshore over time, an opposing force associated with the increasing negative buoyancy eventually balances the PPGF and results in a quasi‐steady upslope flow. The approaching squall line disrupts this flow in two distinct ways; Initially the storm's cold pool enhances the ambient downslope winds which diminishes the upslope wind speeds, and subsequently the storm‐generated high‐frequency waves and the associated surface pressure low enhances the upslope‐directed PPGF which reintensifies the upslope flows. Plain Language Summary: This study uses numerical simulations to investigate the physical processes driving sea breezes over mountainous coastal regions, the sensitivity of the sea breeze evolution to its density and depth, and changes to the sea breeze by approaching organized deep convective storms (i.e., squall lines). Deeper and cooler marine atmospheric boundary layers move farther inland and have stronger wind speeds. The onshore upslope sea breeze is driven by an onshore‐directed pressure gradient force (PGF) induced by the denser marine air. However, as the marine air accumulates onshore over time, its negative buoyancy drives an opposing offshore downslope force that helps to prevent any additional inland advancement of the sea breeze front. An offshore‐moving squall line influences this flow in two ways; Squall line outflow initially weakens the sea breeze but then enhances the sea breeze by decreasing the surface pressure ahead of the sea breeze front through storm‐induced gravity waves. Key Points: Upslope flow is intensified by a moving marine atmospheric boundary layer (MABL), with its features relying on a MABL's depth and densityUpslope acceleration is enhanced by the MABL‐induced perturbation pressure gradient force but is reduced over time by the negative buoyancyThe passage of storm‐generated high‐frequency gravity waves and the associated surface pressure lows temporarily enhance the upslope flow
- Subjects
ATMOSPHERIC boundary layer; SEA breeze; OFFSHORE structures; MOUNTAIN wave; THUNDERSTORMS; GRAVITY waves; SURFACE pressure; WIND speed
- Publication
Geophysical Research Letters, 2023, Vol 50, Issue 6, p1
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2023GL102825