Mesoscale-to-LES Modeling of the Sea-Breeze Front and its Interaction with Turbulent Flows over a Coastal City

Sea-breeze front (SBF) intruding coastal cities can lead to sudden changes in local weather and air quality. Its structures and disturbances over the urban surface with dense tall buildings have been a challenge for numerical modeling. In this study, we present the fine-scale structures of an actual SBF simulated by mesoscale-to-LES models at 3-meter resolution in a 15-km domain of Sendai City, Japan. The head of SBF is shown to develop remarkable three-dimensional structures in the downtown area where it interacts strongly with the microscale turbulent flows induced by buildings. Localized strong updrafts form at the lees of high-rise buildings within a few minutes just after the passing SBF, as ejections emerge in urban warm airmass surrounded by the cool airmass of sea breeze. Downdrafts in sea breeze are seen at the windward sides of high-rise buildings and help to increase wind speed in adjacent streamwise streets. After the passage of SBF, near-surface wind speed exhibit high-frequency fluctuations with a period of 2–3 minutes, in good agreement with in-situ observations in downtown area. These results demonstrate the good capabilities of the building-resolving LES of both mesoscale weather conditions and microscale turbulent flows over a large city for the prediction of urban weather and environment in the streets.