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？许多研究将物理气候和生物地球化学变量观测的双年代际变率与LNC联系起来。特别是在北太平洋及其周围，那里的日潮成分很强，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有重大影响。没有LNC强迫的模式模拟显示了北太平洋强烈的年代际变率内部模态，如太平洋年代际涛动。LNC强迫可以通过以下方式调制这些内部模式：(1)将可变性转移到双进制频率范围，(2)产生共振，或(3)同步它们的相位。该项目将通过海洋混合的调节以及随之而来的对温度和年代际气候变化模式的影响，检验有关LNC潮汐振荡与气候双年代际变化的假设。潮汐混合的全球一致参数化已经在一个中等复杂程度的气候模式中得到验证，并显示会导致气候上显著的海面温度异常，将在一个全面的全球气候模式中实施。该参数化包括一种新的亚网格尺度测深方案，并单独考虑了4种潮汐成分（M2、S2、K1和O1）及其在LNC作用下的时间变化。该模式将用于模拟潮汐混合的LNC振荡对北太平洋的周期扩散率、温度、海洋和大气环流以及年代际变率模式的影响。将对模型结果进行分析，并与现有观测结果进行比较。目前在一个完整的LNC上可获得的卫星高度计数据将进行分析，目的是改进潮汐能量耗散估计、潮汐混合参数化和对正压能量损失机制的理解。更广泛的影响:,# 8232;了解气候变化的强迫机制对于气候的年代际可预测性至关重要。近几十年来，在确定和将气溶胶、太阳和火山变率的影响纳入气候模式方面取得了很大进展。然而，尽管有相当多的文献描述了各种气候变量中18.6年月球交点周期的观测结果，但其影响并未包括在气候模型中。该项目有可能改进在年代际尺度上的气候预测，特别是在北太平洋地区。CCSM4是IPCC评估报告使用的模式之一，在CCSM4中实现月球节点周期对海洋混合的影响将有助于这些具有重要政策相关性的国际报告。模型代码将提供给大型用户社区。北太平洋的年代际变化影响着生态系统和社会。例如，提高对北美西海岸大陆架缺氧事件的可预测性，可能有益于社会，因为这些事件影响到加利福尼亚洋流大型海洋生态系统的生命系统和该地区许多具有重要商业价值的渔业。将促进由具有不同专业知识、背景（全球气候模型、潮汐、耦合的物理-生物区域海洋模型）和性别多样性的三个pi组成的小组之间的合作。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，并提供教学机会。一名本科生将通过暑期实习参与。2014年美国地球物理联合会秋季会议将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.