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.

黑潮洋流的年代际变化是由海洋急流的内在动力学和大气-海洋反馈过程造成的。黑潮在日本南部的独特路径配置与喷流内部不同的内在稳定性状态、黑潮的体积和热量传输的变化以及日本下游黑潮延伸部分（KE）的南北位置有关。这个位置影响海气相互作用的特征和强度，进而反馈黑潮的变化。 这项研究将研究控制路径和稳定状态之间转变的机制，以及内在海洋动力学和影响变异性的海气反馈之间的相互作用。该提案的科学目标是（1）阐明日本南部黑潮路径变率改变 KE 动态的过程，以及它如何与盆地规模风力强迫控制的 KE 变率竞争，（2）阐明最近黑潮大曲流（LM）事件背后的动态，以及（3）量化海面温度（SST）、海温锋和 由于最近 KE 动态变化改变了大气环流而产生的中尺度涡流。该项目将使用面向过程的海洋和大气数值模型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盆地规模的天气模式，两者都具有重要的社会相关性。学生参与和国际合作已在计划中。过去几十年来，高质量卫星/现场观测的积累以及最先进的海洋/大气环流模型的改进极大地提高了人们对KE在十年间北太平洋气候变化中所发挥作用的理解。具体的反馈回路涉及风力驱动的内部海洋温跃层调整、其对KE动态的后续改变以及KE对风暴路径和表面风场的影响。这种风力反馈回路在过去三十年一直在发挥作用，但在 2017 年底被破坏，当时日本南部的黑潮变成了一条大蜿蜒路径，这是西边界流固有变化的表现。已经确定了三个可检验的假设： 假设 1：2017 年 KE 指数反转导致 LM 发生；假设2：2017年LM是由副热带逆流涡旋活动增强引发的；假设3：曲流引起的KE动态反转影响大气。前两个假设将使用 Hallberg 等重模型进行检验，该模型修改为三层配置，其中（a）通过陡峭的底部地形适应层界面的拦截，（b）允许等重层露出海面，以及（c）具有等重坐标以避免非物理二重混合。假设 3 将通过与日本东北大学的 Shusaku Sugimoto 教授合作，使用日本气象厅的非静水力中尺度模型来解决。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。