Collaborative Research: El Nino/Southern Oscillation (ENSO) Predictability--Initial Condition Signal versus Uncoupled Atmospheric Noise

赤道太平洋对天气和气候有着巨大的影响，因为它是厄尔尼诺/南方涛动（ENSO）现象的发源地，其特征是厄尔尼诺事件期间温暖的赤道海面温度（SST）和拉尼娜事件期间寒冷的SST之间的交替。 这些SST变化影响全球大气环流，从而引起长期影响，包括加拿大冬季严酷程度的变化，亚洲季风的降雨分布和大西洋飓风活动。 这些全球性的影响促使人们加紧努力开发ENSO预测系统，这些系统显示出一定的前景，但迄今为止的结果好坏参半。在这里，PI假设ENSO预测的好坏参半是ENSO的内在原因，这意味着某些ENSO事件实际上比其他事件更容易预测。 在这种情况下，“预测技能的预测”，即预先确定厄尔尼诺/南方涛动预测可能准确性的方法，将具有很大的实用价值。 主要研究人员特别关注在事件发生之前所作的ENSO预测的技巧，这些预测的技巧达到了ENSO事件是从某种形式的预处理（如赤道次表层海洋热量的积累）发展而来的程度。 PI先前进行的模式模拟表明，预处理不是ENSO事件的必要条件，ENSO事件可以从中性条件迅速启动。 这种事件纯粹是由大气-海洋系统非常小的初始扰动的混乱增长引起的，从本质上讲是不可预测的。 但PI认为，某些形式的预处理可以使系统不太容易受到噪声水平扰动的影响，而是以确定性的方式驱动厄尔尼诺或拉尼娜事件的演变，允许提前几个月进行巧妙的预测。PI通过社区地球系统模型（CESM）进行的数值模拟来验证他们的假设。 这项工作利用了他们开发的程序，用于在CESM模拟中严格控制赤道太平洋的状态，以便可以施加或排除各种形式的预处理。 其他工作使用PI的交互式Ensemination（IE）技术（例如见AGS-1558837）考虑与ENSO无关的随机天气波动在限制ENSO事件可预测性方面的作用。考虑到ENSO事件的全球影响，这项工作具有社会和科学意义，这项研究的结果对改进ENSO预测的努力有直接影响。为该项目开发的软件连同相关数据集沿着提供给研究界，以便利研究界和业务界采用各种方法和成果。 此外，PI还通过迈阿密戴德学院和美国印第安人高等教育联盟参与针对高中生和大学生的暑期实习计划。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

The equatorial Pacific has an outsized influence on weather and climate as it is home to the El Nino/Southern Oscillation (ENSO) phenomenon, featuring an alternation between warm equatorial sea surface temperatures (SSTs) during El Nino events and cold SSTs during La Nina events. These SST changes affect the global atmospheric circulation and thus induce long-range impacts including changes in the severity of winters in Canada, the distribution of rainfall in the Asian monsoon, and Atlantic hurricane activity. These worldwide impacts have motivated intensive efforts to develop ENSO prediction systems, which show some promise but so far have had mixed results.Here the PIs hypothesize that the mixed success of ENSO predictions is intrinsic to ENSO, meaning that some ENSO events are in fact more predictable than others. In that case a "forecast of the forecast skill", meaning a method to determine in advance the likely accuracy of an ENSO prediction, would have great practical value. The Principal Investigators (PIs) are particularly concerned with the skill of ENSO predictions made before the onset of the event, which are skillful to the extent that ENSO events develop from some form of preconditioning such as the buildup of heat in the subsurface equatorial ocean. Model simulations conducted previously by the PIs suggest that preconditioning is not a necessary condition for ENSO events, which can initiate rapidly starting from neutral conditions. Such events, arising purely from the chaotic growth of very small initial perturbations of the atmosphere-ocean system, would be inherently unpredictable. But the PIs argue that some forms of preconditioning can render the system less susceptible to noise-level perturbations and instead drive the evolution of an El Nino or La Nina event in a deterministic manner, allowing skillful predictions several months ahead of the onset.The PIs test their hypothesis through numerical simulations performed with the Community Earth System Model (CESM). The work takes advantage of procedures they have developed for strictly controlling the state of the equatorial Pacific in CESM simulations, so that various forms of preconditioning can be imposed or excluded. Additional work uses the PI's Interactive Ensemble (IE) technique (see for example AGS-1558837) to consider the role of random weather fluctuations unrelated to ENSO in limiting the predictability of ENSO events.The work is of societal as well as scientific interest given the global impacts of ENSO events, and results of this research have direct bearing on attempts to improve ENSO forecasts. The software developed for the project is made available to the research community, along with relevant datasets, to facilitate adoption of methods and results by the research and operational communities. In addition, the PIs participate in summer internship programs targeting high school and college students through Miami-Dade College and the American Indian Higher Education Consortium.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.