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

Abstract

Sea-breeze front (SBF) can cause dramatic changes in weather and air quality near the coast. However, the observation and forecast of its three-dimensional (3-D) fine-scale structures have been challenging. Using mesoscale-to-large eddy simulations (LES) models and high-resolution lidar measurement over Sendai Airport, here we perform a successful simulation of the observed 3-D structures of an SBF for the first time. We show that frontal structures are characterized by a series of lobes (spaced ~500 m apart) aligned along the raised sea-breeze head, where the shear between sea breeze and alongshore ambient flow aloft is evident. Local strong updrafts occur both in the frontal lobes of marine cold air and in the prefrontal warm air ascending the wedge of windward lobes. Downdrafts form behind the lifted marine cold air and trap air pollutants. These fine-scale structures and vertical motions are repeatedly strengthened by the short-term disturbances of gravity currents that move onshore and collide with the SBF. They are also affected by buildings and determine the detailed variations of surface winds. We conclude that advanced observation and modeling systems can potentially improve the prediction of coastal weather and environment.