Quantifying the Effect of the Lunar Nodal Tide on North Pacific Climate Variability

月球绕地球轨道的变化会影响气候吗？许多研究都将物理气候和生物地球化学变量观测中的双历年变异性与LNC联系起来。特别是在日潮汐成分强烈的北太平洋及其周围，这些观测结果表明，LNC对温度、海洋和大气环流以及生物地球化学循环产生了重大影响。没有LNC强迫的模式模拟表明，北太平洋年代际变化的内部模式很强，例如太平洋年代际涛动。LNC强迫可以通过(1)将变率转换到双半周期频率范围，(2)产生共振，或(3)使它们的相位同步来调制这些内部模式。该项目将通过海洋混合的调制和伴随的对温度和年代际气候变化模式的影响来测试潮汐LNC振荡与气候双年代际变化之间的假设。全球一致的潮汐混合参数化已经在中等复杂性的气候模式中进行了测试，并被证明导致了气候上显著的海表面温度异常，将在一个综合的全球气候模式中实施。该方案包括一种新的亚格子尺度测深方案，分别考虑了四个潮汐分量(M2、S2、K1和O1)及其随LNC的时间变化。该模式将用于模拟潮汐混合的LNC振荡对北太平洋昼夜扩散系数、温度、海洋和大气环流以及年代际变化模式的影响。将对模型结果进行分析，并与现有观测结果进行比较。卫星高度计数据现在可以在一个完整的LNC上获得，将进行分析，目的是改善潮汐能量耗散估计、潮汐混合参数化和对正压能量损失机制的理解。广泛的影响：了解气候变化的强迫机制对于十年气候预测至关重要。近几十年来，在确定气溶胶、太阳和火山变化的影响并将其纳入气候模型方面取得了很大进展。然而，尽管有相当多的文献描述了在各种气候变量中观察到的18.6年的月球节点周期，但其影响并未包括在气候模型中。该项目有可能改进十年时间尺度上的气候预测，特别是在北太平洋区域。在气候变化专门委员会评估报告使用的模型之一CCSM4中实施月球节点周期对海洋混合的影响，将有助于这些具有重大政策意义的国际报告。模型代码将向大型用户社区提供。北太平洋的年代际变化影响着生态系统和社会。例如，提高北美西海岸大陆架缺氧事件的可预测性可能会使社会受益，因为这些事件影响到加州目前的大型海洋生态系统和该区域许多具有重要商业价值的渔业。将促进具有不同专长、不同背景(全球气候模型、潮汐、物理-生物耦合区域海洋模型)和性别多样性的三个私人投资机构之间的合作。一名博士后研究员将接受气候建模和数据分析方面的培训，并获得教学机会。一名本科生将通过暑期实习参与其中。将在美洲地球物理联盟2014年秋季会议上组织一次关于北太平洋年代际变化的会议。

Can variations of the moon's orbit around the earth affect climate? Numerous studies have associated bidecadal variability in observations of physical climate and biogeochemical variables with the LNC. Particularly in and around the North Pacific, where diurnal tide constituents are strong, these observations point towards a significant influence of the LNC on temperatures, oceanic and atmospheric circulation and biogeochemical cycles. Model simulations without LNC forcing show strong internal modes of decadal variability in the North Pacific such as the Pacific Decadal Oscillation. LNC forcing could modulate these internal modes by (1) shifting variability into the bidecadal frequency range, (2) generate resonance, or (3) synchronize their phases. This project will test hypotheses relating LNC oscillations in tides to bidecadal variability in climate via modulations of ocean mixing and attendant effects on temperatures and modes of decadal climate variability.A globally consistent parameterization of tidal mixing, that has already been tested in a climate model of intermediate complexity and shown to lead to climatically significant sea surface temperature anomalies, will be implemented in a comprehensive global climate model. This parameterization includes a new scheme of sub-grid scale bathymetry and separately considers four tidal constituents (M2, S2, K1 and O1) and their temporal variations due to the LNC. The model will be used to simulate the effects of LNC oscillations of tidal mixing on diapycnal diffusivities, temperatures, oceanic and atmospheric circulation, and modes of decadal variability in the North Pacific. Model results will be analyzed and compared to existing observations. Satellite altimeter data, now available over one full LNC, will be analyzed with the goal to improve tidal energy dissipation estimates, tidal mixing parameterizations, and the understanding of mechanisms of barotropic energy loss.Broader Impacts:
Understanding forcing mechanisms of climate change is critically important for decadal climate predictability. In recent decades much progress has been made in identifying and incorporating effects of aerosols, solar and volcanic variability in climate models. However, despite a considerable literature describing observations of the 18.6-year lunar nodal cycle in various climate variables its effect is not included in climate models. This project has the potential to improve climate predictions on decadal time scales particularly in the North Pacific region. Implementing the effect of the lunar nodal cycle on ocean mixing in CCSM4, which is one of the models used by the IPCC assessment reports, will contribute to these international reports of significant policy relevance. The model code will be made available to the large user community. Decadal variability in the North Pacific affects ecosystems and societies. Improved predictability of hypoxic events on the continental shelf of the west coast of North America, for example, may benefit society as these events affect living systems in the California Current Large Marine Ecosystem and many commercially important fisheries in the region. Collaboration between a team of three PIs with different expertise, background (global climate modeling, tides, coupled physical- biological regional ocean modeling) and gender diversity will be fostered. A postdoctoral researcher will be trained in climate modeling and data analysis and given teaching opportunities. An undergraduate student will participate through a summer internship. A session on decadal variability in the North Pacific will be organized at the 2014 Fall Meeting of the American Geophysical Union.