【作者】 徐玲玲；

【导师】 吴德星； 王伟；

【作者基本信息】 中国海洋大学 ， 物理海洋学， 2008， 博士

【摘要】 本文从东中国海的实际海洋物理环境出发,通过数据分析和数值实验等方法对风场与其他外部强迫对东中国海的联合作用进行了机制探讨,并从能量级联的角度初步解释了风场如何通过能量传递的方式控制该海域的环流。首先对海温观测资料和风场、波浪场等卫星数据进行处理,并通过它们之间的对比研究了东中国海温度结构对风场和浪场结构的响应。冬季由于风速较大,东中国海的大多数海域混合充分,等温线几乎垂直于海底;温度的水平结构受水深影响显著,在弱平流及弱上升流的海区几乎都受到“一维热惯性机制”的控制。夏季东中国大多数海域出现温跃层,其上层的混合过程主要受风场控制,混合层深度与海面风场的强弱有很好的对应关系;但近岸及水深较浅的海域大都满足“一维热惯性机制”,甚至在某些有温跃层产生的深水,水深仍然对混合层深度有影响。无论冬季还是夏季,大风天气造成的冷却降温都是明显的。冬季大风在垂直方向使得整个水体继续冷却,水平方向由于混合增强,会使温度锋强度减弱;夏季大风在表面造成的冷却和强混合破坏了跃层结构,使混合层加深,同时减小了表层海水和底层海水之间的温度差。其次,通过数值实验研究了风场和外洋强迫—黑潮对东中国海环流结构尤其是黄海暖流及其季节变化的作用机制。黄东海的主要环流系统由海表面风场和外洋强迫共同控制。黑潮的对马分支驱动出向南的朝鲜沿岸流,由此产生的黄海海区南北压力差及质量守恒约束诱生出向北流动的黄海暖流来补偿,这部分流量约占黄海暖流年平均流量的2/3;同时受季风控制的苏北沿岸流也会驱动出向北的暖流,这部分流量约占黄海暖流年平均流量的1/3。黄海暖流的季节变化主要由季风控制。冬季,西北风造成苏北沿岸流向南的水体输运,同时也增加了朝鲜沿岸流的流量,二者共同造成大量向北的水体输运,补偿作用导致较强的黄海暖流出现;夏季,虽然朝鲜沿岸流仍然流向南,但东南风使苏北沿岸流流向北,二者有部分流量相抵消,使得南北压力差远小于冬季,因此黄海暖流很微弱甚至观察不到。最后从能量传递的角度探讨了风能量如何影响环流。在有限水深的情况下推导了浅海Ekman波的理论解,并在实测资料中进行了应用。风通过Ekman运动输送给东中国海的能量能够从表层向深层传递,向下传递的速度大约为0.0022m /s ;风应力相同的情况下,水越浅,表面向下传递的能通量越少;能量向下传递的过程中,振幅呈e指数衰减,其中近惯性频率能量的衰减程度最小,能够作用于深层混合的能量大部分都位于近惯性频率。风在不同季节向海洋输入能量的大小不仅与风速大小有关,还与风的旋转性有关,旋转性强的风场向海洋输送的能量更多;使用截断频率为0.5cpd的QSCAT资料,经过订正计算出冬季风场通过Ekman运动向东中国海平均输送约2.5GW(1GW=10~9W)的能量;夏季平均输送约4.3GW的能量;风通过表层Ekman运动向东中国海输入的能量中超过1/2都能到达混合层底,约为2.36GW,对温跃层结构的维系起重要的作用。风通过Ekman运动向浅海输送的能量通过湍动能的形式参与到混合当中,其中大约15%能够转化为重力位能;风场异常导致重力位能异常,进一步出现环流异常,由此建立了小尺度的湍动能向大尺度环流能量转化的途径.风场的能量输入对海洋内部运动的意义重大,在水深较深,其它作用机制可能达不到的地方,风场通过能量输入,尤其是近惯性频率的能量输入所造成的影响比较显著;无论重力位能正异常还是负异常,对应环流异常的形态基本上遵循重力位能高值区在右的原则。在北半球,海水由重力位能高值区流向低值区,在流动的过程中受到科氏力的作用,将会围绕高值区产生顺时针的环流;围绕低值区产生逆时针的环流。更多还原

【Abstract】 Based on the physical characteristics of the East China Seas (ECS), various methods are applied to analyze the influence of wind, as well as other exterior forcing on shelf seas. Many phenomena are considered and from the point of energy transforming, the hypostasis of these phenomena are concluded by looking into the observations and numerical model results.During winter time, strong northerly wind controls the ECS. Water in most areas is well mixed and the isotherms are almost vertical to seabed. The horizontal structure of sea surface temperature (SST) is identical with the structure of isobaths, which can be explained by the one-dimensional bathymetric-control mechanism, with exception of some convection or upwelling area. During summer time, thermocline appears in the ECS, and the upper-layer mixing is mainly controlled by wind. Thus, the mixed-layer depth is mainly determined by the intensity of wind. The one-dimensional bathymetric-control mechanism still has some effects in some areas where thermocline exists. Sometimes, the intense wind distinctly induces stronger cooling and reinforces the vertical mixing. It can obviously make the mixed-layer thicker and reduce the temperature difference from bottom to surface.General circulation structures in both the Yellow Sea and the East Sea are mainly controlled by the Kuroshio (KC) and local wind. The KC gives birth to the southward Korean Coastal Current(KCC), indirectly via the Tsushima Warm Current(TSWC), and further induces the northward Yellow Sea Warm Current (YSWC) to compensate the mass loss in north Yellow Sea. This contributes about 2/3 of the YSWC. The effect of wind is also important, which induces about 1/3 of the YSWC by pushing the Chinese Coastal Current (CCC) southward. Besides, the monsoonal forcing dominants the seasonal variability of the YSWC mainly via the CCC.The speed of the energy from wind to the ECS can be calculated in the form of Ekman wave, which depends on the frequency of the wind stress. The Ekman wave travels in the z direction with amplitude decreasing exponentially with depth while energy in near-initial frequency decreases very little. The energy flux is dependent on the water depth when the wind stress is stable. The shallower the water is, the less energy wind transports. The energy flux also has relationships with the rotation of the wind. From calculating, the total energy from wind to the Ekman layer in the ECS is about 2.5GW in winter and 4.3GW in summer using the QSCAT wind vector data with a cutoff frequency of 0.5cpd. Based on the mixed-layer depth from observations, about 2.36GW can reach the bottom of the mixed-layer, more than 1/2 of the energy obtained from wind. Considering the net heat flux in different season, about 15% of the energy from wind can transform to the Gravitational potential energy(GPE). The anomaly of gravitational potential energy (GPE) would induce the anomaly of circulation. In the north hemisphere, the water moves from the region with the greater increase of GPE to that with smaller increase or decrease of GPE. So there appears a clockwise current anomaly around the region where the increase of GPE is larger and an anticlockwise current anomaly around that with smaller anomaly of GPE due to the Coriolis force. This is the channel of the energy transfer from small-scale turbulence to large-scale motions.更多还原