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

海洋热浪(MHW)是极端海洋表面温度(SST)的破坏性时期，扰乱了海洋生态系统和依赖它们的渔业。它们的影响包括加剧国家之间的经济紧张局势，以及威胁公众健康的前所未有的有害藻类水华。在整个全球海洋都观察到了这些事件，在过去十年中，在中纬度地区发生了几次大规模的持续性事件。气候模型模拟表明，在全球持续变暖的情况下，我们可以预期MHW将变得更持久、更频繁和更强烈，推动生态系统超过其热应对极限，导致对环境的不可逆转的影响。虽然过去40年的SST卫星记录可以描述过去MHW的特征，但这些毁灭性的中纬度事件的数量有限，因此很难评估这些事件的不同寻常程度。对个别事件的原因和后果的基于事件的分析使我们能够洞察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。这项研究将利用一组广泛的现有模型模拟，包括不同的模型配置和相似运行的集成或多个实现，以实现更好的统计收敛。这项分析将对海洋关键区域模拟的保真度和热浪的可预测性产生深刻的见解。MHW对人类和自然系统的影响都是深远的，量化气候变化对其性质的影响以及检查这些事件的可预测性最终将有助于缓解和准备应对未来的潜在影响。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，并与NCAR的科学家合作开发用于未来极端海洋事件分析的新工具。研究小组还将与设在华盛顿大学的西北网络海洋观测系统协会(NANOOS)和北卡罗来纳州自然保护协会办公室合作，就这项研究的结果撰写短文。这项研究的结果还将被纳入华盛顿大学和威斯康星大学沿海海洋学和气候学的本科课程。该项目将利用一套使用CESM(共同体地球系统模型)进行的模型模拟，包括在低分辨率和高分辨率下的强迫模拟和耦合模拟。将使用一个由40名成员组成的1920年至2100年气候的大型集合来评估MHW的统计数据，从而允许对事件特征进行统计稳健性。对高分辨率强迫和耦合模拟的额外分析将允许评估在边界电流区的MHW表示的保真度，其中在低分辨率模拟中已知存在较大的偏差。此外，使用与大型集合相同的模式版本的十年预报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指标，或定义为固定框上的面积平均的指标。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下的热量。气候变化在控制MHWs方面的作用将使用大型集合进行评估，而高分辨率模式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MHW的特性。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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 an unprecedented harmful algal bloom that threatened 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 impact 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. Results of this research 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 CESM (Community Earth System Model) 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.