热带气旋及其变异对北太平洋浅层翻转环流的影响机制

A series of research were achieved based on the ongoing NSFC Youth Science Foundation project: the global distribution of sources/sink region of shallow overturning circulation was depicted; the diurnal cycle of mixed layer can greatly enhance the vertical exchange of water mass between ocean surface and subsurface; and tropical cyclones were found to be an important physical process to effectively stir the subsurface water to the ocean surface. The shallow overturning circulation is accompanied with the mass/heat transport and abnormal signal propagation among different latitudes, which is important to modulate the climate. The stirring process and the anomaly of temperature/salinity structure induced by tropical cyclones can both greatly effect the shallow overturning circulation, which is relatively shallow. However, in the previous studies, the effect of tropical cyclones on the shallow overturning circulation was omitted. The present proposal focuses on the effect of tropical cyclones on the North Pacific shallow overturning circulation, and how the variability of tropical cyclones modulates the North Pacific shallow overturning circulation and the associated mass, heat transport. This study will reveal the important role of meso- and small-scale strong nonlinear events in the studies of large-scale oceanic circulation, and then provide the theoretical basis for the further studies of oceanic circulation, climate and their variability.

正在承担的青年科学基金在海洋浅层翻转环流方面取得了一系列成果：构建了浅层翻转环流源、汇区的全球分布图；发现日循环可以显著的加速海洋表层与次表层的水交换；指出热带气旋可以有效地将海洋次表层水搅拌到海洋表层。海洋浅层垂向翻转环流能够完成不同纬度间的质量、热量输送及变异信号的传播，对气候有重要的调制作用。由于浅层翻转环流相对较浅，它会在很大程度上受热带气旋强搅拌过程的影响；同时，热带气旋过境引起的海洋次表层温、盐结构的变异也会影响海洋浅层翻转环流。然而，以往关于浅层翻转环流的研究并没有考虑热带气旋这种强天气过程的影响。本项申请重点研究热带气旋对北太平洋浅层翻转环流的影响机制，以及全球变暖背景下，热带气旋的变异对浅层翻转环流及其导致的不同纬度间质量、热量输送的调控；确立中小尺度强天气过程在大尺度海洋环流研究中的作用，为进一步研究海洋环流和气候系统及其变异提供理论依据。

北太平洋地区由于没有深水形成，浅层经向翻转环流及其导致的质量、热量输送和变异信号的传播对东亚气候的影响是不可忽视的。该项目聚焦台风与浅层翻转环流。研究发现，在西北太平洋的台风频发海区，台风的搅拌作用能有效的将副热带潜沉水团所在深度的次表层水“拔”到海洋表层，成为翻转环流的上升分支之一，在副热带潜沉区与台湾以东海域之间形成了封闭的环流圈。与台风相关的翻转环流分支的强度存在很强的年际时间尺度的变化，该变化主要受（强）台风过程控制，与源区的潜沉率、海气通量关系不大。.我们在海洋对台风的局地响应方面也做了相应的工作，并取得了一些进展：（a）给出了台风过境后海洋冷尾迹的时空分布特征。（b）系统分析并揭示了台风对海洋障碍层的影响机制，指出风场的搅拌作用是台风引起障碍层变异的基础。.本项研究把中小尺度强天气过程的研究与大尺度环流研究有机的结合在一起，确立了中小尺度过程在大尺度环流研究中的重要作用，为进一步深入研究海洋环流与气候系统及其变异提供了理论依据。