一次冷锋过境后的海风三维结构数值模拟

Numerical Simulation of a Sea Breeze Event After the Passage of a Cold Front

为研究大尺度系统风对海风的影响以及海风三维结构特征,利用山东省123个地面自动站资料、青岛地区三十多个内陆及沿海、海岛观测站以及奥帆赛场3个浮标站资料,对2006年8月21日青岛一次海风个例进行了分析,并利用美国俄克拉荷马大学风暴分析预测中心开发的ARPS(the Advanced Regional Prediction System)模式,对海风过程进行了数值模拟研究。结果发现:在较强的离岸风背景下,当内陆气温高于海面气温2℃左右时,海风也可以发生。海风首先在海岸线附近的海上开始,发展的同时向内陆及远海地区推进。海风低层环流很浅,主要位于500 m以下。在较强的偏北离岸风下,海风向内陆推进的距离很短。偏北的大尺度系统风由于渤海冷下垫面的影响,不利于青岛海风的维持。海风开始时,在1500～2500 m高度处同时有反环流出现,但直到傍晚前后,海风的垂直环流圈才发展得比较清晰,其高度也更接近地面。海风消亡后,高层的垂直环流圈及反环流维持3 h左右才逐渐消亡。

A sea breeze event occurs on 21 August 2006 when a cold front passes Shandong Province and the synoptic -scale wind is northerly.In order to analyze the development of the sea breeze,the feature of the sea breeze is analyzed with 123 AWS data in Shandong Province,over 30 AWS station data in Qingdao area,in the island and three buoys in the sailing spots.As a result,the detailed AWS station data in the coastal area and buoys can give more detailed and new feature of the sea breeze.Further more,these data are assimilated into the ARPS（the Advanced Regional Prediction System） model.The controlled experiment uses 2- level 1-way nested grids,with the horizontal resolutions of 30 km and 6 km respectively.In vertical,a scheme consisting of 53 sigma-z levels with a minimum thickness layer of about 20 m near the surface and vertically stretched grids extending to model tops at about 20 km height is used.Compared with the observation, the model can simulate development of the sea breeze reasonably.With the observation and the simulation,the detailed feature of the boundary wind and 3-dimension structure of the sea breeze are analyzed, indicating that the sea-land temperature difference of around 2℃causes the sea breeze in this case. Under the northerly wind,the surface temperature to the south of Qingdao rises faster than that on the north land,thus the sea breeze mainly occurs in the southeast coastal region.The sea breeze begins offshore and then develops into the land and the far ocean widely.The vertical height of the sea breeze circulation is as shallow as below 500 m.Due to the stronger offshore synoptic-scale wind the sea breeze can only spread to very limited area along the coastal line.The northerly synoptic wind passes over the Bohai Sea and causes cold surge to land in Shandong Province,which is adverse for the sea breeze maintaining,as a result,the sea breeze in the southeast coastal region of Shandong Province dies earlier at around 17：00. When the sea breeze begins the reverse circulation forms around 1500—2500 m height at the same time. But the vertical circulation doesn＇t develop clearly until the evening and the height of it is below 1000 m. The vertical circulation and the reverse circulation can last 3 hours after the sea breeze dies.