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.

黑潮的年代际变化是由海洋喷流的内在动力学和大气-海洋反馈过程引起的。黑潮在日本南部的独特路径配置与射流内部的不同稳定性状态、黑潮的体积和热输送的变化以及黑潮延伸（KE）在日本下游的N-S位置有关。这个位置影响海气相互作用的性质和强度，而海气相互作用反过来又反馈给黑潮变率。本研究将探讨路径和稳定状态之间转换的控制机制，以及影响变率的内在海洋动力学和海气反馈之间的相互作用。本研究的科学目标是：(1)阐明日本南部黑潮路径的内在变率改变KE动力状态的过程，以及它如何与盆地尺度风强迫控制的KE变率竞争；(2)阐明近期黑潮大曲流（LM）事件的动力机制；(3)量化海表温度（SST）的相对贡献。海温锋和中尺度涡旋由于近期KE动力状态的变化而改变了大气环流。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变异性。黑潮和KE是气候变率的重要组成部分，影响着北太平洋生态系统和盆地尺度的天气模式，两者都具有重要的社会相关性。学生参与和国际合作的计划。过去几十年来，高质量卫星/原位观测的积累和最先进的海洋/大气环流模式的改进，大大提高了对KE在北太平洋气候年代际变率中所起作用的认识。具体的反馈环包括风强迫海洋内部温跃层调整及其对KE动力状态的改变，以及KE对风暴路径和地面风场的影响。这种在过去30年里一直在起作用的风强迫反馈回路在2017年底被打乱，当时日本南部的黑潮变成了一条蜿蜒的大路径，这是西边界洋流内在变化的一种表现。提出了三个可检验的假设：假设1:2017年KE指数逆转导致LM发生；假设2:2017年低潮是由副热带逆流涡活动增强引发的；假设3：曲流诱导的KE动态状态逆转影响大气。前两个假设将用Hallberg等平模型进行检验，该模型修改为三层结构，其中(a)适应陡峭底部地形对层界面的拦截，(b)允许等平层露出海面，以及(c)具有等平坐标以避免非物理的等平混合。假设3将通过与日本东北大学Shusaku Sugimoto教授的合作，使用日本气象厅的非流体静力中尺度模型来解决。该奖项反映了美国国家科学基金会的法定使命，并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。