Collaborative Research: Midlatitude Marine Heatwaves in a Changing Climate: Variability, Predictability, and Projections

海洋热浪（MHWs）是极端海面温度（SST）的破坏性时期，破坏海洋生态系统和依赖它们的渔业。其影响包括国家之间的经济紧张局势加剧，以及威胁公众健康的前所未有的有害藻类大量繁殖。这些事件已在全球海洋中观察到，在过去十年中，在中纬度地区发生了几次大规模的持续事件。气候模型模拟表明，在持续的全球变暖下，我们可以预期MHW将变得更持久，更频繁和更强烈，推动生态系统超越其热应对极限，对环境造成不可逆转的影响。虽然过去40年的SST卫星记录可以描述过去的MHW，但这些破坏性的中纬度事件的数量有限，因此难以评估这些事件的异常程度。对个别事件的原因和后果进行基于事件的分析，使人们能够深入了解控制这些特定事件的重要过程，但这些过程在未来是否仍然重要尚不清楚。这项研究将利用一系列广泛的现有模型模拟，包括不同的模型配置和集合或类似运行的多个实现，以实现更好的统计收敛。该分析将深入了解海洋关键部分模拟的保真度和热浪的可预测性。MHWs对人类和自然系统的影响是深远的，量化气候变化对其属性的影响以及对这些事件的可预测性的检查最终将有助于减轻未来的潜在影响并为之做好准备。两名研究生将接受培训，以使用国家大气研究中心（NCAR）的分析工具，以及与NCAR的科学家在Python开发新的工具，用于未来的极端海洋事件的分析工作。该研究小组还将与华盛顿大学主办的网络海洋观测系统西北协会（NANOOS）和北卡罗来纳州自然保护办公室合作，撰写有关这项研究结果的短文。研究结果还将纳入华盛顿大学和威斯康星州大学的沿海海洋学和气候本科课程。该项目将利用利用社区地球系统模型进行的一套模型模拟，包括低分辨率和高分辨率的强迫和耦合模拟。将使用1920年至2100年的40个成员的大型气候系综对MHWs的统计数据进行评估，以使事件特征具有统计稳健性。高分辨率强迫和耦合模拟的额外分析将允许评估边界电流区域中MHW的表示的保真度，其中已知在低分辨率模拟中存在大的偏差。此外，使用与大型集合相同的模式版本的十年预测系统将允许探索海洋初始化在这些危险事件的可预测性中的作用。MHW属性的典型分析使用逐点度量，或定义为固定框上的面积平均值的度量。将创建用于MHW表征的新的综合指标，允许MHW随时间改变形状和位置，并将考虑储存在表面以下的热量。气候变率在控制MHW中的作用将使用大型集合进行评估，而高分辨率和低分辨率模式的比较将允许评估低分辨率模式结果的稳健性。对中纬度事件的关注将包括评估海洋热储存和重新出现如何影响MHWs的属性。该奖项反映了NSF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。

Marine heatwaves (MHWs) are devastating periods of extreme sea surface temperatures (SST) that disrupt marine ecosystems and the fishing industries that rely on them. Their effects include increased economic tension between nations and unprecedented harmful algal blooms that threaten public health. These events have been observed throughout the global ocean, with several large scale persistent events occurring in the mid-latitudes over the last decade. Climate model simulations suggest that under continued global warming we can expect MHWs to become longer lasting, more frequent and intense, pushing ecological systems beyond their thermal coping limit, leading to irreversible impacts to the environment. While the satellite record of SST over the last 40 years allows characterization of past MHWs, the number of these devastating midlatitude events is limited, making it difficult to assess how unusual the events are. Event based analysis of the causes and consequences of individual events has given insight into important processes that control these particular events, but whether these processes remain important in the future is unclear. This research will make use of an extensive set of existing model simulations, including both different model configurations and ensembles or multiple realizations of similar runs for better statistical convergence. The analysis will yield insights into both the fidelity of the simulations in critical parts of the ocean and the predictability of heat waves. The impacts of MHWs are profound to both human and natural systems, and quantifying both the effect of climate change on their properties as well as an examination of the predictability of these events will ultimately help to mitigate and prepare for potential impacts in the future. Two graduate students will be trained to use the National Center for Atmospheric Research (NCAR) analysis tools, as well as work with NCAR scientists in developing new tools in Python for use in future analyses of extreme ocean events. The research team will also work with the Northwest Association of the Networked Ocean Observing Systems (NANOOS), hosted at the University of Washington, and the North Carolina Nature Conservancy office to write short articles about the results of this research. The results will also be incorporated into undergraduate courses in coastal oceanography and climate at the University of Washington and the University of Wisconsin.This project will take advantage of a suite of model simulations performed using the Community Earth System Model (CESM) including forced and coupled simulations at both low and high resolutions. An assessment of statistics of MHWs will be performed using a 40-member large ensemble of the climate from 1920 to 2100 allowing statistical robustness of event characteristics. Additional analysis of high resolution forced and coupled simulations will allow assessment of the fidelity of the representation of MHWs in boundary current regions where large biases are known to exist in low resolution simulation. In addition, a decadal prediction system using the same model version as the large ensemble will allow exploration of the role of ocean initialization in the predictability of these dangerous events. Typical analysis of MHW properties has used pointwise metrics, or metrics defined as area averages over fixed boxes. New integrated metrics for MHW characterization will be created that allow for MHWs that change shape and position over time, and will take into account heat stored below the surface. The role of climate variability in controlling MHWs will be assessed using the large ensemble, while comparison of high and low resolution models will allow for assessment of the robustness of the results from low resolution models. The focus on midlatitude events will include assessment of how ocean heat storage and re-emergence affect properties of MHWs.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.