Seasonal And Interannual Variations Of The Water Temperature In The Yellow Sea And East China Sea

The in-situ observations of the water temperature during1960-2000are used tointerpretthe seasonal and interannual variations and the spatial distributions of thewater temperature in the Yellow Sea and East China Sea (YSECS).Firstly, several quality control methods are conducted to guarantee the datareliability. According to the geographical features and the numbers of availabledata, fifteen sub-regions are defined to study the time-spatial variations of watertemperature in recent40years in the YSECS.Significant seasonal variations are found in the layers shallower than100m, ofwhich the most striking difference is located at the sea surface. As the depthincreases, the amplitude of water temperature variation becomes smaller, theseasonal warming trend of temperature slows, and the time of the appearance ofhighest temperature delays. The time of highest and lowest temperature at the seasurface is different. The four areas along Kuroshio path and the middle area ofYellow Sea (YS) reach the highest temperature first. The areas at Tsushima Straitreach the highest temperature last.Annually, there is a warming trend in winter temperature in most areas. But it is acooling trend in winter temperature that occurs in area A and B at East China Seashelf (ECSS),300-400m of area B at Kuroshio path and200-400m of area C atKuroshio path which is lower than-0.05°C/a. In summer, warming trend is alsofound in most areas except the layers deeper than100m in the entrance ofKuroshio in the East China Sea (ECS), layers below50m in area B of Kuroshiopath, area off Changjiang River estuary,20-30m of area south of Jeju, area west of Jeju, eastern part of South Yellow Sea and Tsushima Strait. Significant correlationsare found in interannual variations of sea surface temperature (SST) both amongareas in the YS and among areas along Kuroshio path. But variations of SST in theareas along Kuroshio path show poor correspondence with thosein YS.Vertically, thermocline of three areas along Kuroshio path is stronger during1977to1990. The thermocline of the East China Sea Continental and area off theChangjiang River estuary is weaker from1970to1980and stronger from1980to1985. The thermocline of eastern part of South YS (SYS) and middle part of YS isstronger from1980to1990. Most of the thermoclines are affected by temperatureat both upper level and lower level. However, thermocline in west part of south YSis only effected by upper level temperature (correlation coefficient R=0.88).Thermoclines in the entrance of Kuroshio in the East China Sea, area A and Calong Kuroshio path, area A on the ECSS and eastern part of SYS are only foundcorrelate to the temperature of upper levels. Root Mean Square (RMS) in winter issimilar to each other in the same area of different levels. In summer, RMS is largerat the middle level and the largest RMS is located around thermocline or font.Secondly, four representative sections are defined to analyze their amplitudes ofinterannual water temperature variability. The results are as follows: In winter, theRMS of water temperature from the surface to bottom is similar at each section.With respect to PN section, the largest RMS appears to be at PN-4station. As to thesection of31°N and33.5°N, the amplitude at West is larger than that at East.Section of36°N has larger amplitudes at122°E-122.5°E and the stations near theeastern coast. In summer, the largest RMS happens to be at the middle depth. AtPN section, the50m-75m level has the largest interannual variations, andtemperature is rising except30-200m at PN-3station. Section of31°N has thelargest amplitude at the west of the section and the variation is the biggest at depth of20m. It is the same as to the section of33.5°N. But for the section of36°N, thelargest amplitude is exactly where14°C-16°C isotherm locates.Thirdly, the temperature variation can be divided into two period,1980-1985named cold period and1990-1995named warm period. The water temperaturedifference between above two periods at the depth of0m,50m and200m iscalculated to analyze the distribution of water temperature. It is found thattemperature in winter is warmer except at areas around200m isobaths. In summer,temperature in the Yellow Sea and Bohai Sea is higher, but the temperature of theeast part along the Korea is a little lower. Plus, temperature of areas along the200m isobaths is lower at depth of0m and200m, but higher at depth of50m.Temperature at200m from28°N-38°N becomes colder compared to1980-1985.