Secular Changes in Pacific Tides

智力优势：全球海平面上升（GSL）是有据可查的。然而，极端高水位（HHW）的变化，包括潮汐贡献，与GSL上升一样相关。潮汐记录的分析表明，在东北太平洋（18 - 60ºN），全日和半日振幅都以每百年2.2%的速度增长。总潮汐振幅的平均增加（每年0.59毫米）小于GSL上升（每年1.7毫米）。然而，空间平均海平面（MSL）上升是小的东北太平洋，潮汐演变起着重要作用的变化在HHW。潮汐演变的空间格局表明大尺度过程的影响，并似乎排除机制与强烈的频率依赖性。可能的影响的重要性和变化的大规模性质需要一个分析，包括多个潮汐两栖动物。这将允许检查潮汐振幅增加和减少的区域的过程，并促进原因的调查。具体而言，我们将评估整个太平洋潮汐振幅的数据变化，并通过数值模拟确定可能的原因。研究人员将执行以下任务：1）方法，数据来源和初步分析：从成分复振幅的时间序列中提取长期趋势（和趋势的可能变化）的最有效方法是什么？有几个站的记录长度（LOR）大于50年，大约9年和18.6年的变化，潮汐特性不完全遵循天文强迫，复杂的分析。优化分析方法以充分利用稀缺数据至关重要。将使用调和方法从潮汐数据和潮汐势中提取成分，然后对潮汐导纳进行回归分析，以进行涵盖所有主要昼夜和半日成分的分析。将使用复解调法分析选定岛屿和沿海台站若干潮汐带的相干和非相干能量。2)时空模式：潮汐性质在空间和时间上如何变化？我们将客观地绘制（使用经验正交函数或正交函数）潮汐演变的空间模式，并确定潮汐振幅变化是否显示类似于GSL上升的加速度。有些台站还表现出明显的大幅度气候反应，例如对厄尔尼诺-南方涛动（ENSO）事件的反应，这些反应很容易检测。其他国家则显示每年的入学周期。这些反应是关于长期趋势原因的重要线索。3)潮汐振幅长期变化的原因是什么？将使用正压和三维模型来检验观测到的大规模变化是否可能是由以下原因引起的：a）由于风的变化而影响潮汐的背景涡度变化，或B）与变化中的海洋分层的相互作用，导致斜压和正压潮汐能的时变平衡。我们还将研究变化的陆架分层在改变沿海被困波，内部和表面潮汐的相互作用的作用，因为这可能是一个重要的因素，导致空间变化的顶部的无潮尺度的变化。4)综合：导致潮汐快速演变的实际机制是什么？任务3中的概念见解必须与任务1和任务2中的分析结果相结合，以确定这一点。更广泛的影响：潮汐振幅的增加可能会影响海洋混合、营养供应、初级生产、渔业、沿海基础设施和海岸侵蚀。潮汐性质的变化模式也可能是全球气候变化的一个重要的，但迄今尚未认识到的症状。波特兰州立大学（PSU）认识到其学生，教师和工作人员的多样性是其最宝贵的资源之一。多样性行动招聘和保留团队（DAHRT）将协助招聘研究生和博士后助理。此外，拟议的工作将促进早期职业科学家的成长。

Intellectual Merit: Global sea level (GSL) rise is well documented. However, changes in extreme Higher high water (HHW), including the tidal contribution, are just as relevant as GSL rise. Analysis of tidal records shows that the diurnal and semi-diurnal amplitudes are both growing at 2.2% per hundred years in the NE Pacific (between 18 to 60ºN). The mean increase in total tidal amplitude (0.59 mm per year) is less than GSL rise (1.7 mm per year). However, spatially averaged mean sea level (MSL) rise is small in the NE Pacific, so tidal evolution plays a major role in changes in HHW. The spatial pattern of tidal evolution suggests the influence of large-scale processes, and seems to exclude mechanisms with strong frequency dependence. The importance of the possible impacts and the large-scale nature of the changes demand an analysis that encompasses multiple tidal amphidromes. This will allow examination of processes in areas with both increasing and decreasing tidal amplitudes, and facilitate investigation of causes. Specifically, we will evaluate from data changes in tidal amplitudes for the entire Pacific Ocean and determine likely causes through numerical modeling. The investigators will carry out the following tasks: 1) Methods, data sources and preliminary analyses: What is the most efficient method to extract secular trends (and possible changes in trends) from time series of the constituent complex amplitude? There are few stations with length of record (LOR) greater than 50 years, and roughly 9 and 18.6 year variations in tidal properties do not exactly follow astronomical forcing, complicating analysis. Optimizing analysis methods to make the best use of scarce data is vital. A harmonic method of constituent extraction from both the tidal data and tidal potential, followed by a regression analysis of the tidal admittance, will be used in an analysis that covers all major diurnal and semidiurnal constituents. Complex demodulation will be used to analyze coherent and incoherent energy in several tidal bands at selected island and coastal stations. 2) Space-time patterns: How do tidal properties vary in space and time? We will objectively map (using empirical orthogonal functions or EOF) spatial patterns of tidal evolution and deter-mine whether tidal amplitude changes show acceleration analogous to GSL rise. Some stations also exhibit apparent, large-amplitude climate responses, e.g. to ENSO (El Niño-Southern Oscillation) events, that are easy to detect. Others show annual cycles of admittance. These responses are important clues regarding causation of secular trends. 3) Causation: What are the causes of secular changes in tidal amplitudes? Barotropic and three-dimensional models will be used to test whether the observed large-scale changes could be caused by: a) changes in background vorticity affecting the tides due to changes in winds, or b) interactions with changing ocean stratification resulting in a time-varying balance of baroclinic and barotropic tidal energy. We will also investigate the role of changing shelf stratification in altering the interaction of coastal trapped waves, and internal and surface tides, because this is likely a significant factor causing spatial variations on top of the amphidromic-scale changes. 4) Synthesis: What are the actual mechanisms causing tides to evolve rapidly? Conceptual in-sights from Task 3 must be combined with analysis results from Tasks 1 and 2 to determine this. Broader Impacts: Increasing tidal amplitudes may impact ocean mixing, nutrient supply, primary production, fisheries, coastal infrastructure, and coastal erosion. Changing patterns of tidal properties may also be a significant, but heretofore unrecognized, symptom of global climate change. Portland State University (PSU) recognizes diversity among its students, faculty, and staff as one of its most precious resources. The Diversity Action Hiring and Retention Team (DAHRT) will assist in recruiting a graduate student and Post-Doctoral Associate. In addition, the proposed work will foster the growth of an early-career scientist.