Identifications and analyses of characteristics for sea and land Breeze circulations in the Bohai Rim Region

Abstract

As the closest sea to the Capital of China, the Bohai Rim region inside the Yellow Sea over complex underlying surfaces is important to the international trade, logistics and environment. It's necessary to depict the detailed three-dimensional spatial structures and temporal evolvements of sea and land breeze (SLB) circulations over this region with complicated coastlines before interpreting their meteorological contributions to extreme weather, climate and environment events. In this study, an identification approach is developed to seize SLB circulations from high resolution datasets in the Bohai Rim region. Improvements are made to replace the wind decomposing algorithm with a newly developed one which is applicable to highly complicated flows over complex underlying surfaces. SLB events in this region of 2022 are identified from 1-km model simulation data along the C-curvature coastline which is separated into the middle, northeastern and southwestern parts. Quantified and comparative analyses are performed in the form of characteristic quantities. Firstly from the mean perspective, quantities such as frequency, duration time, intensity, height, and penetration distance are adopted to investigate the spatial features of both sea breeze circulations and land ones along the three coasts. It is found that both frequencies and intensities of sea breeze events are higher than their correspondences of land ones. Distinctions among the three coasts are evident, with SLB events along the southwestern coast presenting the highest frequency and the strongest intensity. Secondly, temporal evolvements of SLB circulations are investigated along the three coasts at their start, strongest and end stages. Vertical heights of SLB circulations increase from the start stage to the strongest one, and then decrease till the end one. The vertical motion during sea breeze events along the northeastern coast is the strongest at the start and strongest stages. Thirdly, comparative analyses of sea breeze circulations along the three coasts are carried out under onshore and offshore background winds. Under onshore winds, the middle and southwestern coasts experience stronger sea breeze events, while weaker events influence the northeastern coast in the form of smaller horizontal penetration distances and larger vertical heights.