Intrinsic versus Forced Decadal Variability in the Extratropical North Pacific

温带北太平洋的内在与受迫年代际变率

• 批准号: 2019312
• 负责人: Bo Qiu
• 金额: $ 48.94万
• 依托单位: University of Hawaii
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-08-01 至 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2019312&HistoricalAwards=false
• 关键词: Intrinsic; versus; Forced; Decadal; Variability

Decadal variability of the Kuroshio Current results from both the intrinsic dynamics of oceanic jets and from atmosphere-ocean feedback processes. The Kuroshio’s distinct path configurations south of Japan are associated with differing states of intrinsic stability within the jet, with variations in volume and heat transport by the Kuroshio, and with the N-S position of the Kuroshio Extension (KE) downstream from Japan. This position affects the character and intensity of air-sea interactions, which in turn feed-back upon Kuroshio variability. This study will examine the mechanisms controlling shifts between paths and stability states, and the interplay between intrinsic ocean dynamics and air-sea feedbacks affecting variability. The scientific goals of the proposal are to (1) clarify the processes by which the intrinsic Kuroshio path variability south of Japan alters the KE dynamic state and how it competes with the KE variability controlled by the basin-scale wind forcing, (2) elucidate the dynamics underlying a recent Kuroshio large meander (LM) event, and (3) quantify the relative contributions of sea surface temperature (SST), SST fronts and mesoscale eddies due to the recent KE dynamic state change in modifying the atmospheric circulation. The project will use process-oriented oceanic and atmospheric numerical modeling to address the system variability. The Kuroshio and KE are important components of climate variability, influencing North Pacific ecosystems and basin-scale weather patterns, both of important societal relevance. Student involvement and international collaboration are planned.Accumulation of high-quality satellite/in-situ observations and improvement in state-of-the-art ocean/atmosphere general circulation models over the past decades have significantly improved understanding of the roles played by the KE in the decadal North Pacific climate variability. The specific feedback loop involves the wind-forced interior ocean thermocline adjustment, its subsequent alteration to the KE dynamic state, and the KE’s influence on the stormtracks and the surface wind field. This wind- forced feedback loop, which had been at work in the past three decades, was disrupted in late 2017 when the Kuroshio south of Japan changed to a large meander path, a manifestation of intrinsic western boundary current variability. Three testable hypotheses have been identified: Hypothesis 1: The 2017 KE index reversal caused the LM occurrence; Hypothesis 2: The 2017 LM was triggered by enhanced Subtropical Counter Current eddy activity; and Hypothesis 3: Meander-induced KE dynamic state reversal impacts the atmosphere. The first two hypotheses will be examined with the Hallberg Isopycnal Model, modified to a three-layer configuration, which (a) accommodates the interception of layer interfaces by steep bottom topography, (b) allows sea-surface outcropping of isopycnic layers, and (c) has isopycnal coordinates to avoid unphysical diapycnal mixing. Hypothesis 3 will be addressed using the Japan Meteorological Agency’s non-hydrostatic mesoscale model, through a collaboration with Prof. Shusaku Sugimoto of Tohoku University, Japan.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

黑潮的年代际变率是海洋急流的内在动力学和海气反馈过程共同作用的结果。黑潮在日本以南的独特路径配置与急流内不同的内在稳定性状态、黑潮的体积和热量输送变化以及黑潮延伸体（KE）在日本下游的南北位置有关。这个位置影响海气相互作用的性质和强度，反过来又反馈到黑潮的变化。 这项研究将审查控制路径和稳定状态之间变化的机制，以及内在海洋动力学和影响变率的海气反馈之间的相互作用。该提案的科学目标是：（1）阐明日本以南黑潮路径变化改变KE动力状态的过程，以及它如何与流域尺度风强迫控制的KE变化竞争，（2）阐明最近黑潮大弯曲（LM）事件的动力学，（3）量化海表温度（SST）的相对贡献。由于近期动能动力状态的改变而引起的SST锋和中尺度涡旋对大气环流的影响。该项目将使用面向过程的海洋和大气数值模拟来解决系统的可变性。黑潮和KE是气候变率的重要组成部分，影响北太平洋生态系统和流域尺度的天气模式，两者都具有重要的社会意义。在过去几十年中，高质量的卫星/现场观测的积累和最先进的海洋/大气环流模式的改进，显着提高了对KE在十年期北太平洋气候变率中所起作用的理解。具体的反馈回路包括风强迫的内部海洋温跃层调整，其随后的改变KE动力状态，和KE的风暴路径和地面风场的影响。这种风力驱动的反馈回路在过去三十年中一直在发挥作用，但在2017年底被打乱，当时日本以南的黑潮变成了一条大的弯曲路径，这是固有的西部边界流变化的表现。已经确定了三个可检验的假设：假设1：2017年KE指数逆转导致LM的发生;假设2：2017年LM是由副热带逆流涡动活动增强触发的;假设3：曲折引起的KE动态逆转影响大气。前两个假设将用修改为三层结构的Hallberg等密度模型进行检验，该模型（a）可容纳陡峭海底地形对层界面的拦截，（B）允许等密度层露出海面，（c）具有等密度坐标，以避免非物理的贯向混合。假设3将通过与日本东北大学杉本修作教授的合作，使用日本气象厅的非静力学中尺度模式进行研究。该奖项反映了NSF的法定使命，通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。