Interaction between turbulent flow and sea breeze front over urban‐like coast in large‐eddy simulation

• Published in: Journal of geophysical research. Atmospheres Vol. 122; no. 10; pp. 5298 - 5315
• Main Authors: Jiang, Ping, Wen, Zhiping, Sha, Weiming, Chen, Guixing
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 27-05-2017
• Subjects: Boundary layers; Buildings; Buoyancy; Climatology; Coastal environments; Computational fluid dynamics; Computer applications; convective boundary layer; Daytime; Dynamics; Fluid dynamics; Fluid flow; Fluxes; Geophysics; Hydrodynamics; Large eddy simulation; Measuring instruments; Mixed layer; Oceanic eddies; Offshore; Offshore engineering; Penetration; sea breeze; Sea breezes; Shear; Simulation; Structures; Turbulence; Turbulent flow; Turbulent fluxes; Updraft; urban; Velocity; Vortices; Vorticity; Weather; Wind shear
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1002/2016JD026247

Turbulent flow and its interaction with a sea breeze front (SBF) over an urban‐like coast with a regular block array were investigated using a building‐resolving computational fluid dynamics model. It was found that during daytime with an offshore ambient flow, streaky turbulent structures tended to grow within the convective boundary layer (CBL) over a warm urban surface ahead of the SBF. The structures were organized as streamwise streaks at an interval of a few hundred meters, which initiated at the rooftop level with strong wind shear and strengthens in the CBL with moderate buoyancy. The streaks then interacted with the onshore‐propagating SBF as it made landfall. The SBF, which was initially characterized as a shallow and quasi‐linear feature over the sea, developed three‐dimensional structures with intensified updrafts at an elevated frontal head after landfall. Frontal updrafts were locally enhanced at intersections where the streaks merged with the SBF, which greatly increased turbulent fluxes at the front. The frontal line was irregular because of merging, tilting, and transformation effects of vorticity associated with streaky structures. Inland penetration of the SBF was slowed by the frictional effect of urban‐like surfaces and turbulent flow on land. The overall SBF intensity weakened after the interaction with turbulent flow. These findings aid understanding of local weather over coastal cities during typical sea breeze conditions.
Key Points
Fine‐scale turbulent flow and sea breeze front are explicitly resolved in large‐eddy simulation
Streaky turbulent structures form over urban surface with strong wind shear and moderate buoyancy
Streaky turbulent structures render sea breeze front into 3‐D structures with strengthened updrafts