渤、黄、东海冬季海表冷暖水舌的时空变化及机理分析

Temporal and spatial variations of the surface cold and warm tongues in the Bohai,Yellow and East China Seas and their formation mechanism

海表冷暖水舌被广泛应用于定性描述海表水温(SST)的空间分布特征,但缺少定量的表述和研究。本文以海表冷暖水舌轴线的空间位置和温度为指标,用2006—2014年逐年冬季(2月)的遥感SST数据,分析了渤海、黄海和东海冬季的冷暖水舌的空间分布和年际变化,并探讨了其形成机理。结果表明,渤海、黄海和东海冬季存在2条冷水舌和6条暖水舌。水舌位置的EOF前三个模态(73.4%)基本解释了其年际变化,其中空间第一模态呈同相分布,在东海中部及西部的变动幅度最大;空间第二和第三模态主要呈反相分布,分别在九州岛南部及黄海区域变动幅度较大。水舌温度的EOF第一模态(69.6%)呈空间同相分布,变动幅度在渤、黄海较大,在东海南部较小。水舌位置和水舌温度都存在准2~3a周期的年际变化,但只有水舌位置EOF第二模态通过95%水平的显著性检验。海表相对较均匀的负净热通量(海洋向大气输送热量),使得浅水区SST比深水区下降得快,水深(上混合层深度)是冷暖水舌形成的原因之一;平流热输送的空间差异显著且在冷暖水舌区域中的作用最大,在冷舌区域起到降温作用,在暖舌区域起到增温作用,平流热输送是冷暖水舌形成的主要原因。

The surface cold and warm tongues are used as a key characteristic to describe the spatial feature of SST.However,that characteristic is often used qualitatively rather than quantitatively because of lacking quantitative parameters.In this paper,we use nine years（2006-2014）merged microwave and infrared SST data to analyze quantitatively the spatial and temporal variations of the surface cold and warm tongues in the Bohai,Yellow and East China Seas（BYES）.The characteristics of the surface cold and warm tongues are expressed in terms of their path and associated temperature.Two cold tongues and six warm tongues are identified in the BYES in February.The Empirical Orthogonal Function（EOF）analysis shows that the total variance of the path of tongues is explained mostly by the three leading EOF modes（73.4%）.Specifically,the first spatial mode of path shows that every tongue moves coherently in same direction,and the most significant movement occurs in the central and the west of East China Sea.In contrast,the second and third spatial modes show that most tongues move with a seesaw pattern,and the most significant movement occurs at the south of Kyushu and in the Yellow Sea respectively.The total variance of temperature on the path of tongues is explained mostly by the first EOF mode（69.6%）,which has a coherent increase or decrease of temperature in each tongue with a large amplitude in the Bohai and Yellow Seas.Both the path and associated temperature of the tongues have a 2-3year inter-annual variation,however only the second EOF temporal mode of the path has passed the significant test.In winter,the relatively even loss of the heat in the sea leads to a much faster decrease of SST in the shallow area than in the deep area and forms cold and warm patterns associated with the bathymetry of the BYES.The uneven advectional heat transport plays a different role at various areas to reinforce and compensate the decrease of SST.In the cold tongue area,the advectional heat transport reinforces the heat loss of the water and leads to a much colder SST than the surrounding area,consequently forms the cold tongues.In contrast,in the warm tongue areas,the advectional heat transport compensates the heat loss of the water and leads to a much warmer SST than the surrounding area,consequently forms the warm tongues.The advectional heat transport plays a major role at the formation of the cold and warm tongues in the BYES.