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

Abstract

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.

Sea Breeze Sensitivity to Coastal Upwelling and Synoptic Flow Using Lagrangian Methods

“…The propagation of the sea breeze front onshore is slower than the propagation of the sea breeze cell offshore, especially earlier on at 1700–2000 UTC. This asymmetric propagation pattern may be attributed to a difference in turbulence/frictional effect between land and sea (Jiang et al, ; Sha et al, ). The end result is that the sea breeze cell begins at a width of about 30 km centered on the coast and slowly and relatively symmetrically expands onshore and offshore to about a width of nearly 250 km after 7 hr.…”

“…Journal of Geophysical Research: Atmospheres between land and sea (Jiang et al, 2017;Sha et al, 1991). The end result is that the sea breeze cell begins at a width of about 30 km centered on the coast and slowly and relatively symmetrically expands onshore and offshore to about a width of nearly 250 km after 7 hr.…”

Structures of the Sea‐Breeze Front in Dual‐Doppler Lidar Observation and Coupled Mesoscale‐to‐LES Modeling

“…These results suggest that, in the presence of coastal sparse buildings, the building‐induced small eddies can disturb the coherent features of mesoscale gravity currents, producing the local disturbances in frontal structures and winds. This situation differs somewhat from that of a densely built‐up area, where the SBH is elevated due to surface drag (Jiang et al, ; Thompson et al, ).…”

“…The sensitivity of the model results to the above settings will be discussed in section . To simulate the life cycle of a gravity current disturbance, the CFD simulation was run for 30 min with a time step of 1 s. Meanwhile, random cell perturbations were input into the initial field to achieve a fast growth of boundary layer turbulence (Jiang et al, ; Muñoz‐Esparza et al, ). The cell perturbations continued to work at the lateral boundary and disturb the inflow during the simulation.…”

“…Journal of Geophysical Research: Atmospheres for 30 min with a time step of 1 s. Meanwhile, random cell perturbations were input into the initial field to achieve a fast growth of boundary layer turbulence (Jiang et al, 2017;Muñoz-Esparza et al, 2014). The cell perturbations continued to work at the lateral boundary and disturb the inflow during the simulation.…”