西太平洋邊緣海波浪-環流耦合數值模式之發展(I)
No Thumbnail Available
Date
2010-07-31
Authors
吳朝榮
Journal Title
Journal ISSN
Volume Title
Publisher
行政院國家科學委員會
Abstract
海洋包含了各種不同時空尺度、不同特性的運動型態 (海浪、潮汐、海流等)， 如何將不同運動整合於單一海洋數值模式之中，以儘量保持模擬海洋運動的完整 動力過程，是一個重要的課題。具體地來說，臺灣周邊海域冬季受到強勁東北季 風下的影響，勢必會形成洶湧的海面波浪，其強烈的攪拌作用，海氣交界面的大 量擾動，對臺灣海峽的水團混合、混合層深度、水文特性分布有何影響？在台灣 東側的黑潮在不同季節受到波浪的影響如何，是否會使得垂直混合的效果更強， 流場又如何變化？甚至一直以來都相當重要的海氣交互作用，波浪過程的加入是 否可以改善對海洋混合層熱量的模擬估算，進一步是否可以增進大氣模式的結 果，改進天氣預報或颱風預報的準確度？這些問題不僅僅需要考慮一個單純的海 流數值模式，更需要結合波浪理論與動力機制來加以研究，建立一個耦合波浪、 環流動力過程的海洋模式才得以解答上述問題。因此，本計畫的主要目的是要透 過波浪-環流耦合的技術改進現有的東亞邊緣海模式（East Asian Marginal Seas, EAMS），提升對環臺海域水文、波浪、流場模擬的能力。將新建構的東亞邊緣 海波浪-環流耦合模式將同時需要有海洋環流模式與波浪模式，海流模式部分將使 用已經建構完成且具有良好模擬結果的東亞邊緣海模式；在波浪模式方面將會使 用由中國海洋局第一海洋研究所最新發展的 MASNUM（key laboratory of MArine Science and NUmerical Modeling）波浪模式來提供波、流耦合的耦合參數。研究 的目標是以符合動力過程的方法結合波浪模式與海流模式，建立臺灣周邊海域波 流耦合模式，藉以瞭解臺灣周邊海域的物理現象、海洋環境、動力過程等。
Ocean movements include waves, tides, and currents. Different framework has been designed to describe each separated motion in the past. However, there are interactions among these movements. For example, most of ocean circulation models often underestimate the surface mixing and mixed-layer depth, which is extremely important for the small-scale coastal simulations and large-scale global climate simulations. Thus, a lot of efforts attempt to improve mixing processes for the circulation models. Adding either a Richardson number-dependent mixing below the mixed layer (Kantha and Clayson, 1994) or a Richardson number-dependent dissipation (Ezer, 2000; Mellor, 2001) improve the simulation to a certain degree. However, the achievements in general are not sufficient for all case studies. A new approach is to couple a circulation model and a wave model. In this study, we will establish a theoretical framework to include the influences of surface waves into a circulation model. An expression for wave-induced fluctuation as a function of wave number spectrum is derived for coupling of a circulation model and a wave number spectrum model. A wave-induced viscosity (or diffusivity) obtained from a third-generation wave number spectrum numerical model (e.g. Yang et al., 2005) will be coupled to our high-resolution ocean circulation model (e.g. Wu and Hsin, 2005; Wu et al., 2008). Intercomparisons will be made among the observations, the model without the wave effects, and the coupled wave-circulation model. Different approaches for the wave-circulation parameterizations will be tested to improve the model mixed-layer and dynamics.
Ocean movements include waves, tides, and currents. Different framework has been designed to describe each separated motion in the past. However, there are interactions among these movements. For example, most of ocean circulation models often underestimate the surface mixing and mixed-layer depth, which is extremely important for the small-scale coastal simulations and large-scale global climate simulations. Thus, a lot of efforts attempt to improve mixing processes for the circulation models. Adding either a Richardson number-dependent mixing below the mixed layer (Kantha and Clayson, 1994) or a Richardson number-dependent dissipation (Ezer, 2000; Mellor, 2001) improve the simulation to a certain degree. However, the achievements in general are not sufficient for all case studies. A new approach is to couple a circulation model and a wave model. In this study, we will establish a theoretical framework to include the influences of surface waves into a circulation model. An expression for wave-induced fluctuation as a function of wave number spectrum is derived for coupling of a circulation model and a wave number spectrum model. A wave-induced viscosity (or diffusivity) obtained from a third-generation wave number spectrum numerical model (e.g. Yang et al., 2005) will be coupled to our high-resolution ocean circulation model (e.g. Wu and Hsin, 2005; Wu et al., 2008). Intercomparisons will be made among the observations, the model without the wave effects, and the coupled wave-circulation model. Different approaches for the wave-circulation parameterizations will be tested to improve the model mixed-layer and dynamics.