北太平洋热带海区低维拟序水文结构的诊断研究

The applicant previously applied Gravest Empirical Mode (GEM) method in geophysical flows and established a theoretical model for the observed low-dimensional coherent structure. This project plans to apply the GEM method to the low-latitude North Pacific by diagnosing hydrographic casts as well as mooring measurements. The study region is divided into the equatorial zone and the tropical zone, and plans to combine historical hydrographic data with Argo profiles for GEM analysis, and obtain the spatio-temporal distribution of low-dimension coherent structure in streamfunction space. The inter-relation between coherent structure and various physical processes will then be examined, including the evolution of deep equatorial water during ENSO cycle and the vertical structure of westward propagating mesoscale eddies in the tropical ocean. Meanwhile, the study will use mooring and IES array observations to study the influence of oceanic waves and eddies on the coherent hydrographic structure, and explain the observed baroclinic stability of coherent structure from a dynamical viewpoint. The project will also develop altimetric GEM method and use it to monitor the thermohaline variability in deep ocean.

申请人在前期工作中应用地转经验模态方法发现地球流体存在低维拟序结构并建立了相关动力学理论模型。本项目拟将该方法应用于北太平洋低纬度海区，计划从水文数据诊断和潜标观测分析两方面开展工作，将研究区域划分为赤道海区和热带海区两部分。项目一方面融合历史水文数据和Argo浮标剖面数据进行地转经验模态诊断，分析流函数空间低维拟序结构的时空分布特征，在此基础上探讨不同区域物理海洋过程与水文拟序结构的内在关系, 包括赤道太平洋深层水体在ENSO循环中的演化以及热带西太平洋海区中尺度涡旋的垂直结构等；另一方面，利用关联项目在西太平洋暖池区域布放的深海潜标系统和吕宋海峡区域布放的逆式回声仪观测阵列，研究罗斯贝波和中尺度涡对拟序水文结构的影响，从动力学角度解释拟序结构所具有的斜压稳定性特征，进一步发展基于卫星高度计海表高度场的地转经验模态方法并用以反演海洋深层水文变异。

项目应用地转经验模态方法诊断赤道西太平洋的水文数据，证实赤道海区缺乏垂向的一致相关性且赤道水体呈弱相关层状分布，在此基础上发展了一种非定常地转经验模态投影，应用该方法反演赤道深层水体超过40%的温盐变化；在理论研究方面，给出了椭圆坐标系到笛卡尔坐标系的显式变换方程，可将椭圆坐标系流函数分布直接映射到物理空间；建立了描述旋转流体拟序结构的定常准平面理想流模型并求解多项式精确解，从中发现了层化流体一种新的拟序结构现象，即当涡旋场向以准平面速度为特征的层流状态演变时，涡旋中心垂直排列趋于与重力方向一致；项目提出一种有别于经典水动力稳定性的几何稳定性概念，能够从稳定性角度解释涡旋场垂直拟序和轴对称化现象。