Monitoring Global Ocean Heat Content Changes by Internal Tide Oceanic Tomography

海洋热含量（OHC）是反映全球气候变率和变化的重要指标。然而，在全球范围内观察热含量是一个巨大的挑战。随着Argo剖面浮子阵列的成熟，在空间和时间上具有良好覆盖范围的观测仅在最近10年才得以实现。这项研究将利用一种名为“内部潮汐海洋层析成像”（ITOT）的方法，获得1995年至2014年20年的全球热含量变化记录，其中卫星测高数据用于精确测量远程内部潮汐的传播时间。就像声波断层扫描一样，通过分析这些传播时间来推断热含量的变化。这种分析将使Argo浮标的10年时间序列翻倍。更重要的是，ITOT将为全球热含量变化提供一个独立、长期、低成本、环保的观测系统。由于海洋变暖显著导致海平面上升，这对低洼沿海地区有重大影响，因此这些观测结果具有直接社会效益的潜力。该项目将直接向公众公布部分成果。该小组将制作一部教育动画，展示如何测量海洋变暖，以及从太空的有利位置如何使用新的ITOT技术。该动画将在学生参观实验室时播放，并在当地K-12学校的科学讲座和节日中播放。此外，三名暑期本科生将接受数据分析和解释以及海报展示方面的培训。该项目将在全球海洋上应用的分析技术是基于该小组已经进行的初步区域分析。将分析1995年至2014年约60个卫星年的高度计数据。具体而言，该研究将(1)量化全球M2和K1内部潮的年变率、年际变率和双年代际趋势，(2)构建内部潮旅行时间变化与热含量变化的转换函数，(3)构建20年全球热含量变化记录，并利用Argo测量值评估不确定性。该项目的最终目标是开发用于未来全球热含量监测的ITOT技术。这将提高我们对全球热含量时空变化的理解，特别是结合Argo浮标、xbt和WOCE全深度水文测量的现场测量。ITOT观测将对ECCO2提供有用的限制。内部潮汐模式可用于校正Argo和XBT测量中的内部潮汐噪声。此外，每月和每年产生的内部潮汐场将为全球高分辨率、允许涡流的内部潮汐数值模型提供限制。

Ocean Heat Content (OHC) is a key indicator of global climate variability and change. However, it is a great challenge to observe OHC on a global scale. Observations with good coverage in space and time are only available in the last 10 years with the maturing of the Argo profiling float array. This study will obtain a 20-year-long record of global OHC changes from 1995-2014 with a method called Internal tide oceanic tomography (ITOT), in which the satellite altimetry data are used to precisely measure travel times for long-range internal tides. Just like in acoustic tomography, these travel times are analyzed to infer changes in OHC. This analysis will double the 10 years of time series available from Argo floats. More importantly, ITOT will provide an independent long-term, low-cost, environmentally-friendly observing system for global OHC changes. Since ocean warming contributes significantly to sea level rise, which has significant consequences to low-lying coastal regions, these observations have the potential for direct societal benefits. The project will communicate some of its results directly to the public. The team will make an educational animation showing how ocean warming is measured and how the novel ITOT technique works from the vantage point of space. This animation will be played for students visiting the lab, and in science talks and festivals in local K-12 schools. In addition, three summer undergraduate students will be trained in data analysis and interpretation, and poster presentation.The analysis technique to be applied over the global ocean in this project is based on the preliminary regional analysis already conducted by this team. About 60 satellite-years of altimeter data from 1995-2014 will be analyzed. Specifically, it will (1) quantify annual variability, interannual variability, and bidecadal trend in global M2 and K1 internal tides, (2) construct the conversion function from the internal tide's travel time changes to OHC changes, and (3) construct a record of 20-year-long global OHC changes, and assess uncertainties using Argo measurements. The ultimate goal for this project is to develop the ITOT technique for future global OHC monitoring. This will improve our understanding of the temporal and spatial variability of global OHC, particularly in combination with in situ measurements from Argo floats, XBTs, and WOCE full-depth hydrography. The ITOT observations will provide useful constraints to ECCO2. The internal tide models may be used to correct internal tide noise in the Argo and XBT measurements. In addition, the monthly and yearly internal tide fields produced will provide constraints to global high-resolution, eddy-permitting numerical models of internal tides.