报告题目：On Dynamical Decomposition of Multiscale Oceanic Motions and Submesoscale Dynamics
报 告 人 ：刘志宇 厦门大学教授，博士生导师
报告人简介：刘志宇，厦门大学教授，博士生导师，海洋与地球学院副院长。2009年博士毕业于中国海洋大学（物理海洋学专业），曾获得国家自然科学基金优秀青年科学基金（2016），入选国家“万人计划”青年拔尖人才（2020）。从事海洋动力学基础理论研究，在海洋湍流生成机理与参数化、海洋能量串级机理等方面取得系列成果，在JPO、JFM、GRL等国际权威期刊发表论文46篇（被权威期刊论文引用830次）。现为国家自然科学基金委创新研究群体骨干成员，国际海洋研究委员会（SCOR）第160工作组成员，主持承担国家自然科学基金重大研究计划重点支持项目等，并担任Frontiers in Marine Science、Geoscience Letters、Ocean Dynamics、Journal of Oceanography编委，Acta Oceanologica Sinica主编助理，及亚洲大洋洲地球科学学会（AOGS）出版委员会委员等职。
报告摘要：To date, large uncertainties remain in the quantitative understanding of oceanic energy transfers. For example, the routes and fluxes of downscale energy transfer away from balanced mesoscale motions and the dissipation of low-mode internal gravity waves (IGWs) are inadequately constrained. Reducing uncertainties in oceanic energy pathways relies on our understanding of the dynamics of multiscale oceanic motions, including the tangled interactions among various dynamical regimes and scales of motion. A robust decomposition of multiscale motions in realistic oceanic settings is crucial to advancing dynamical interpretation and prediction of oceanic processes but remains a great challenge.
In this talk, I will present our recent work on the decomposition of multiscale oceanic motions, the associated energy transfers with a special focus on submesoscale motions, and the applicability of the decomposition methodology to next-generation altimetric data from the perspective of aliasing. I will first introduce the methodology we have developed for decomposing multiscale oceanic motions (which include large-scale currents, barotropic tides, mesoscale motions, submesoscale flows, and internal gravity waves of different scales) by virtue of their dynamical characteristics. The application of the methodology is illustrated using numerically simulated flows extracted from a global, tide-resolving and submesoscale-admitting configuration of MITgcm (i.e., LLC4320). Once surface features of low-mode IGWs and balanced mesoscale motions are reconstructed from the simulated sea surface height (SSH), their subsurface manifestations can be inferred according to their vertical modal structures or other dynamically-imposed constraints. Analysis of the decomposed flows suggests that submesoscale variabilities in the Kuroshio extension and Subtropical Countercurrent (STCC) regions fall into distinct dynamical regimes, being characterized by unbalanced and balanced submesoscale dynamics, respectively. I will highlight that it is the unbalanced submesoscale flow that facilitates the downscale transfer of kinetic energy through interacting with mesoscale motions. Using the diagnosed momentum balance, we can derive surface velocity from submesoscale SSH. I will also revisit the aliasing phenomenon in the wavenumber-frequency domain by subsampling the hourly output of LLC4320 according to the designed resolution of next-generation altimetry missions. This, in the context of the IGW continuum, extends the one-dimensional features of temporal aliasing that are routinely used to extract internal tidal signals from altimetric SSH. Obstacles in decomposing multiscale motions from the upcoming wide-swath altimetric data will be highlighted.
报告时间：2021年9月10日（周五）上午10:00
报告地点：2号楼1201会议室
主 持 人：彭世球 研究员
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