Stability analysis of the western boundary currents in the tropical Indian Ocean

热带印度洋西边界流的稳定性分析

• 批准号: 0927472
• 负责人: Jurgen Theiss
• 金额: $ 29.96万
• 依托单位: Theiss Research
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-03-01 至 2015-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0927472&HistoricalAwards=false
• 关键词: Stability; analysis; western; boundary; currents

The overall objective of the project is to understand better the instabilities of the western boundary currents in the tropical Indian Ocean, which are the Somali Current in the Northern and the East African Coastal Current in the Southern hemisphere. This will in particular allow for determining whether the instabilities of these currents contribute to the generation of Yanai waves, also known as mixed Rossby gravity waves, in the western Indian Ocean. Yanai waves, which have the characteristics of Tropical Instability Waves, have been observed in the Pacific, Atlantic, and Indian Ocean. While the generation mechanism is well understood in the Atlantic and Pacific Ocean, it is still practically unknown in the Indian Ocean. This knowledge gap is the main motivation for the work.The project will employ the classical normal mode stability theory, which considers exponential growth processes as for instance in the theory of baroclinic instability, and the comparatively new Generalized Stability Theory, which encompasses also transient growth processes. To investigate the instabilities of the western boundary currents in the tropical Indian Ocean three models will be used: A modified form of the quasigeostrophic model, the equatorial counterpart of the quasigeostrophic model recently developed by Theiss and Mohebalhojeh, and the Regional Ocean Modeling System (ROMS).The overall objective inspires two additional objectives. The first additional objective is to investigate whether the equatorial counterpart of the quasigeostrophic model is for instability studies in the equatorial region a tool that is as instructive as the quasigeostrophic model in the mid-latitudes. The second additional objective is to integrate the project with the PIs' Zanzibar Project, which is an educational project for students on coastal oceanography in East Africa. The natural overlap of the study of the western boundary currents of the tropical Indian Ocean and coastal oceanography in East Africa will be used by the PIs for the mutual benefit of both projects and especially the involved students.Better understanding the instabilities of the western boundary currents in the tropical Indian Ocean and in particular their contribution to the generation of Yanai waves would help towards developing a level of understanding that already exists about the generation of Yanai waves in the Atlantic and Pacific Ocean. Dominant features such as the alternating Monsoon winds must affect the instabilities of the western boundary currents in the tropical Indian Ocean. These instabilities in turn must affect the marine ecosystems along the East Coast of Africa and might contribute to the generation of Yanai waves, thus effect the momentum and heat balance in the equatorial Indian Ocean and climate variability. The instabilities are therefore an integral part affected by and in turn affecting processes with scales ranging from local to ocean-basin-wide. In addition, the integration of the study with the PIs educational Zanzibar Project will help expand the students' study of the coastal ocean of East Africa to the larger western tropical Indian Ocean.

该项目的总体目标是更好地了解热带印度洋西部边界海流的不稳定性，即北方的索马里海流和南半球的东非沿岸海流。这将特别有助于确定这些海流的不稳定性是否有助于西印度洋产生柳井波，也称为混合Rossby重力波。柳井波具有热带不稳定波的特征，在太平洋、大西洋和印度洋都有观测到。虽然大西洋和太平洋的生成机制已经很清楚，但印度洋的生成机制实际上仍然未知。该项目将采用经典的正常模式稳定性理论，该理论考虑指数增长过程，例如斜压不稳定性理论，以及相对较新的广义稳定性理论，其中也包括瞬态增长过程。为了研究热带印度洋西部边界流的不稳定性，将使用三种模式：准地转模式的改进形式、Theiss和Mohebalhojeh最近开发的准地转模式的赤道对应模式以及区域海洋模拟系统（ROMS）。第一个额外的目标是调查是否赤道对应的准地转模式是在赤道地区的不稳定性研究的一个工具，是作为指导性的准地转模式在中纬度地区。第二个额外目标是将该项目与方案研究所的桑给巴尔项目结合起来，后者是为东非沿海海洋学学生举办的教育项目。热带印度洋西部边界流和东非沿海海洋学研究的自然重叠将被PI用于两个项目的共同利益，特别是参与的学生。更好地了解热带印度洋西部边界流的不稳定性，特别是它们对生成柳井波的贡献，将有助于提高理解水平已经存在的关于柳井波在大西洋和太平洋的产生。主导功能，如交替季风风必须影响热带印度洋的西边界流的不稳定性。这些不稳定性反过来必然会影响沿着非洲东海岸的海洋生态系统，并可能促成柳井波的产生，从而影响赤道印度洋的动量和热量平衡以及气候变化。因此，不稳定性是一个不可分割的组成部分，它受到从地方到整个海洋盆地范围的各种过程的影响，并反过来影响这些过程。此外，将这项研究与国际和平研究所的教育桑给巴尔项目结合起来，将有助于将学生对东非沿海海洋的研究扩大到更大的西热带印度洋。