【作者】 李威；

【导师】 马继瑞； 刘克修； 韩桂军；

【作者基本信息】 中国海洋大学 ， 物理海洋学， 2008， 博士

【摘要】 首先采用较强的海洋温度锋判别标准,利用研究海区的温度断面观测资料提取了温度锋信息,并参考了有关水文图集和文献,分析表明台湾以东表层温度锋不明显,而水下却终年存在较强的黑潮温度锋。然后对研究海区的海面高和三维温盐流进行了气候态数值模拟,由数值模拟结果获得的台湾以东温度锋的结果,同利用观测资料和图集分析得到的结果在趋势上是一致的,即台湾以东从次表层至350m存在较明显的黑潮温度锋。该锋随深度加深,其强度和宽度均呈先增大后减小的趋势；该温度锋的位置存在随深度加深而逐渐向东偏移的趋势；且具有季节变化,其强度和宽度夏季达到最大,冬季较弱。提取了中国海及邻近海域卫星遥感海面温度(SST)资料中的温度锋信息,如果采用强标准,则台湾以东表层温度锋不明显。为了深入研究台湾以东水下温度锋的时空多尺度变化规律及其形成变化机制,进行了海面高和三维温盐流数值再分析。再分析中采用开发的并行化混合坐标POMgcs海洋模式,发展了一种适合海洋锋面分析的全三维空间多重网格三维数据同化方法。该方法通过引入平滑惩罚项,解决了存在的“牛眼”现象,保证了同化效果的客观性；可以依次提取不同波长的信息,解决了传统三维变分数据同化仅提取特定波长信息的问题；并由于在三维空间实现了变分数据同化,克服了由于分层同化而造成的虚假分析梯度的缺点。采用同样的海洋温度锋判别标准,提取了上述海洋再分析结果中的温度锋信息。提取的台湾以东黑潮温度锋的气候态统计结果与上述结果基本一致。由最大熵谱分析得知,该温度锋除了存在显著的年周期外、还存在显著的2.1a、195d、124d、90d、59d多尺度变化周期。利用本文再分析及其温度锋信息提取结果,研究了台湾以东黑潮温度锋的形成变化机制。认为台湾以东黑潮携带着大量的高温高盐水,黑潮暖平流使台湾以东上层水温增高,加大黑潮流轴两侧水下温度的梯度。与此同时,台湾以东沿岸上升流较强,上升的冷水与黑潮高温水相汇,形成较强的水平温度梯度,因此在台湾以东近岸形成了黑潮温度锋。分别通过对该温度锋强度与黑潮流量及其与上升流流速的交谱分析表明,黑潮流量越大或上升流流速越强,该温度锋就越强。上升流和黑潮流量均在夏季最强,在两者共同作用下,使这一带的水下黑潮温度锋在夏季较强。诊断分析发现,上升流对该温度锋的贡献约为黑潮暖平流的3倍,认为上升流是该温度锋的主要形成变化机制。上升流约在200m层达到最大值,而从200m水层以上至表层的上升流逐渐减小到几乎为零,因此台湾以东表层几乎不存在明显的温度锋,但在次表层温度锋较强。研究还表明,冷涡(暖涡),会使得台湾以东黑潮温度锋右侧水温降低(升高),减弱(增强)锋面两侧温度梯度,从而削弱(增强)台湾以东黑潮温度锋强度,减小(加大)锋的宽度。对再分析结果中的一次锋面波动进行了研究,通过对其能量来源的诊断分析表明,正压不稳定的贡献与斜压不稳定的贡献比K-H不稳定大1-2个数量级,而斜压不稳定的贡献约为正压不稳定的5倍,因此该锋面波动基本上由斜压不稳定性提供能量。更多还原

【Abstract】 In this paper, based on the stronger judgment criterion for oceanic thermal front, the thermal front information is extracted from the temperature profile observations in the study area. By using the hydrographical atlas and referring to related literatures, the temperature distribution trend of different levels is also analyzed. The results show that the surface thermal front to the east of Taiwan is not obvious, while there is an all-year strong Kuroshio thermal front under the surface. The sea surface height (SSH),3-dimensional (3D) temperature, salinity and current in that area are numerically simulated. And the final result is consistent in the tendency with that from observations and atlas. There is more obvious Kuroshio thermal front from subsurface to 350m to the east of Taiwan; with depth increasing, both intensity and width of this thermal front has the tendency of decrease following increase; and the position of such thermal front tends to be eastward with the depth’s increasing; such front is characterized by seasonal changes that the strongest strength and width are in summer and the weakest in winter.The oceanic thermal front information is extracted from the satellite remote sensing sea surface temperature (SST) data of China Seas. It is found that the surface thermal front is not obvious if the strong criterion is adopted. In order to study the 3D multi-scale temperature variation rule of the Kuroshio front under the surface to the east of Taiwan and discuss the mechanism of frontogenesis, the SSH,3D temperature, salinity and current are numerically reanalyzed in this frontal zone. The paralleled hybrid coordinates POMgcs is applied in this reanalysis. A new full-space multi-scale data assimilation method applicable to the analysis of the ocean front is developed. Through adopting the penalized smooth term, the "bull’s eye" is settled, which ensures the objectivity of this new method. This new method can extract different wave-length information in turn and can make full-space 3D variational (3D-Var) data assimilation, so it overcomes the shortcomings of the traditional 3D-Var data assimilation method which only extracts the specific wavelength information and results in false analysis gradient due to the stratified assimilation.As for the reanalysis results above, by using the same stronger judgment criterion for oceanic front, the oceanic thermal front information is extracted. The climatology statistic results of the Kuroshio thermal front to the east of Taiwan are basically consistent with the above simulated results. From the maximum entropy spectral analysis, this thermal front not only has the significant annual cycle, but also has the significant multi-scale variation cycle, like 2.1a,195d,124d,90d and 59d.By using the reanalysis results and the extracted thermal front information, the frontogenesis and changing mechanisms of the Kuroshio thermal front to the east of Taiwan are studied. The Kuroshio to the east of Taiwan carries vast water with high temperature and high salinity, and the Kuroshio warm advection raise the water temperature at the upper level ocean to the east of Taiwan, which can enlarge the gradient of the water temperature at the both side of the current axis of the Kuroshio. At the same time, the upwelling is strong due to water depth varying sharply in the coast to the east of Taiwan, and the elevating cold water convenes with the high-temperature Kuroshio water, forming stronger horizontal temperature gradient, thereafter, the Kuroshio thermal front is created in the offshore area to the east of Taiwan. The cross spectral analysis of the thermal front intensity and the Kuroshio flux and that of thermal front intensity and the upwelling velocity of flow show that the stronger the upwelling and the Kuroshio flux are, the stronger the intensity of the Kuroshio thermal front is. Because the upwelling and the Kuroshio flux are strongest in summer, the Kuroshio thermal front under the surface caused by the cooperation of them in this area is the strongest in summer. It is found through the diagnostic analysis that the contribution of the upwelling to this thermal front is three times than that of the Kuroshio warm advection, that is to say, the upwelling is the main mechanism for the frontogenesis and maintenance of this thermal front. The upwelling velocity reachs its maximum at 200m level and from this level to surface reduces to almost zero. Therefore, the surface thermal front to the east of Taiwan is not obvious while the subsurface frontal intensity is stronger. The presence of vortex may influence this thermal front. The result indicates that cold vortex (warm vortex) can reduce (raise) the water temperature to the right of the Kuroshio thermal front to the east of Taiwan, and weaken (strengthen) the bilateral temperature difference of the front, thereby weaken (strengthen) the strength of the Kuroshio thermal front to the east of Taiwan and narrow (widen) the width of this front.The frontal wave in the reanalysis result is studied in this paper. It is found through the diagnostic analysis of the energy source of the frontal wave that the contribution of barotropic instability or that of baroclinic instability is more than that of K-H instability by 1-2 order of magnitude, and the contribution of the baroclinic instability is 5 times than that of the barotropic instability, thereby the frontal wave is basically driven by the baroclinic instability.更多还原