Spatiotemporal Variation And Mechanism Analysis Of The Surface Of The Hot And Cold Water In The Bohai Sea

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. Based on merged cloud-penetrating microwave and infrared (MWIR) OI SST data from 2006 to 2014, the research gave a quantitative description of the temporal and spatial variations of the cold and warm tongues in terms of their path and associated temperature. The mean path and temperature of the surface cold and warm tongues were calculated and described at first, then the variations of path and temperature anomaly of the surface cold and warm tongues in interannual scale were analyzed with the EOF analysis methods. At last, the contributions of the heat advection to the variations of temperature of the surface cold and warm tongues were calculated.Two cold tongues and six warm tongues were identified in the Bohai, Yellow and East China Seas (BYES) in February. The path of cold tongue in the northern East China Sea is much closer than in southern East China Sea. The closest region of warm tongue is the Bohai Strait, followed by coast in northeastern Taiwan. Relatively, warm tongues in northern Kyushu are most dispersive. The temperature of cold and warm tongues in south part of the area is relatively higher than in the north and that in shallow area is relatively lower than in the deep area. The highest standard deviation is near the Yangtze River estuary and in the northern Yellow Sea, followed by the Zhe-Min coast and the central Yellow Sea.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 East China Sea. In contrast, the second and third spatial modes show that every tongue moves 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 cold and warm,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 2-3 year interannual 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, and forms the warm tongues. The advectional heat transport plays a major role at the formation of the cold and warm tongues in the BYES.