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海洋科学学术沙龙第73期顺利举行:Open boundary conditions for tidally and subtidally forced circulation in a limited-area coastal model using the Regional Ocean Modeling System (ROMS)

   浏览数:33   日期:2018年06月25日

6月24日,我院学术沙龙第73期(2018年第8期)在珠海校区教学楼A404会议室举行。本期沙龙由靳光震研究员发起并主持,特邀香港科技大学环境和可持续发展学部的刘志强研究助理教授及香港科技大学数学系的蔡忠亚博士后作报告。海洋科学学院来志刚教授、罗一鸣教授以及学院各学科方向的师生共15人参加了本次沙龙。

本次沙龙首先围绕Open boundary conditions for tidally and subtidally forced circulation in a limited-area coastal model using the Regional Ocean Modeling System (ROMS)”一主题进行讨论,报告以自主研发的T&ST边界条件为例,探讨新型边界条件对海洋数值模型开边界存在多重信号传递时的处理效果。刘志强研究助理教授主要阐述了传统flather边界条件只允许潮汐信号穿越边界的不足之处,提出将边界信号的潮汐部分和非潮汐部分分离处理的新型TST边界条件,并将其成功应用在东海近岸的海洋数值模拟中,证明TST边界条件有能力改善亚潮信号的误差积累问题。随后,蔡忠亚博士后对南海海流的垂向分布特征进行机制分析,提出内部跨陆坡运动和beta效应是其关键形成因素,而后进一步建立三维模型模拟南海涡链,并基于涡度平衡提出了新的解释。报告人和与会人员就数值计算、模型验证和方法应用前景等问题展开热烈讨论。沙龙最后,现场师生对刘志强研究助理教授以及蔡忠亚博士后所做的报告再次表达了衷心的感谢。

刘志强研究助理教授介绍其科研成果

蔡忠亚博士后介绍其科研成果

现场提问环节

合影留念(左五为蔡忠亚博士,左六为刘志强研究助理教授)

海洋科学学院学术沙龙旨在促进各学科方向之间的学术交流、情感交流、思想交流,为广大师生搭建一个眼界更加开阔、立意更为高远的交流平台,从而进一步激发大家在学术研究中追求卓越的雄心,为推动“三大”建设,实现学校百年目标的宏伟事业贡献力量。

附(报告摘要):

报告一题目: Open boundary conditions for tidally and subtidally forced circulation in a limited-area coastal model using the Regional Ocean Modeling System (ROMS)

摘要:

In limited-area ocean models, open boundary conditions (OBCs) often create dynamic inconsistencies and perform poorly in resolving tidal or subtidal flow when both forces exist. Orlanski-type radiation OBCs are reasonably efficient at treating the subtidally forced flow, and Flather-type OBCs are commonly adapted for the tidally forced flow. However, neither of them performs well when tidal and subtidal forces simultaneously drive the flows. We have developed a novel OBC that integrates the active OBC in Gan and Allen (2005) and a Flather-type OBC. This new OBC accommodates the concurrent Tidal and Subtidal (TST) forcing, and the respective tidal or subtidal forcing, at the open boundary of a limited-area model. This new TST-OBC treats the tidal component with a Flather-type OBC, and it separates subtidal barotropic and baroclinic components into local (forced) and global (unforced) components. Then an unforced Orlanski-type OBC can be applied to the global part. We applied the TST-OBC to all model variables to reduce dynamic inconsistence. Using the Regional Ocean Modeling System, we applied the TST-OBC to the shallow East China Sea shelf where strong tidal and subtidal forces over complex topography govern the circulation. Our numerical experiments and analyses suggest that the TST-OBC was robust for both concurrent tidal-subtidal forcing and solely tidal or subtidal forcing at the open boundary. It reduced spurious energy reflection, and, overall, it performed better than an Orlanski-type or Flather-type OBC in reproducing realistic tidal and subtidal shelf circulation.

报告二题目:On the Formation Dynamics of Layered-Circulation and Long-Lived Eddy-Train in the South China Sea: Modeling Study

摘要:

This research conducts process-oriented numerical study to investigate (1) responses of the layered circulation to the external forcing of inflow/outflow through straits around the South China Sea (SCS) and the internal vertical transport linking and sustaining the circulations among the layers; and (2) the formation of long-lived eddy-train associated with boundary current separation.

Vertical inflow-outflow-inflow through Luzon Strait provides a planetary vorticity flux for the layered-circulation, in which the flux is transported by the three-dimensional slope current and balanced by the vorticity induced by the flow-slope interaction and nonlinear advection inside the SCS. During the development of the layered circulation, the downward/upward transport in the upper/lower layer is established over the slope, which acts as the source/sink of water mass and redistributes the intruding vorticity in the water column. The vertical transport is largely associated with the cross-slope motion induced by bottom friction, nonlinear advection and pressure gradient force (PGF). Driven by the separated jet current, the eddy-train with three anti-cyclonic eddies is generated along jet’s path. The inherent stratification regulates the three-dimensional scale of eddies, and constrains their intensities and vertical extensions. The eddy-train’s negative vorticity is originated from the beta effect of the northward-flowing western boundary current, and from the subsequent downstream vorticity advection along the jet. The jet separation is a necessary condition for the formation of eddy-train, and the enhanced stratification, increased wind forcing are favorable conditions for the formation of eddies.