Observational analyses of a penetrating sea-breeze front in the Beijing-Tianjin-Hebei urban agglomeration

Abstract

A number of simulation studies show that the sea-breeze fronts (SBFs) that form at the Bohai Bay coast can penetrate far inland through the Beijing-Tianjin-Hebei urban agglomeration (BTH). However, there has been little observational evidence for this claim. Based on dense surface observation networks, we observed a SBF that penetrated 170 km inland from Bohai Bay, interacting with cities in the BTH. The SBF was retarded in urban areas compared to surrounding areas, leading to the front line bending in urban areas. The nocturnal surface air temperature of both urban and rural stations increased temporarily as the SBF passed. Urban roughness effects caused strong updrafts during the passage. Ceilometers observed that the strong updraft of the SBF lifted near-surface aerosols to form sea-breeze heads (SBHs), leading to higher SBHs in urban areas than in rural areas. The uplifted aerosols gradually formed thin aerosol plumes, and produced clouds about four hours after the SBF passed. Our observations will help to improve understanding of the interactions between inland SBFs and cities, and provide a basis for further research on the physical mechanisms of how the inland SBF affects aerosols, clouds, and precipitation in the BTH and elsewhere.