The Role of Extratropical Cooling in Determining the Level of El Nino-Southern Oscillation (ENSO) Activity

这项研究解决了厄尔尼诺-南方涛动（ENSO）活动水平如何响应温带太平洋变冷/变暖的问题。最近对 ENSO 在热带太平洋热平衡中的作用的研究提出了温带变冷/变暖在决定 ENSO 活动水平方面发挥根本作用的可能性。这些研究表明，ENSO 充当热泵——一种向下和极地的传热机制——调节热带海洋/大气耦合的时间平均状态的稳定性。温带太平洋的变冷/变暖会改变热带太平洋的热平衡，并通过“海洋隧道”或“大气桥”（连接热带地区和温带地区的大气和海洋环流）扰乱热带海洋-大气耦合系统的稳定性。工作假设是，温带变冷会导致ENSO活动增强，相反，温带变暖会减弱ENSO变化。 这种温带扰动会引发 ENSO 活动水平的响应，因为 ENSO 充当调节赤道太平洋地区长期稳定的热泵。 PI 计划通过进行不同复杂程度的数值实验来检验这一假设。该活动的智力价值：该研究将有助于了解控制ENSO活动水平的全球力量，确定ENSO在十年和更长时间尺度上变化的原因，并揭示ENSO与平均气候之间的相互作用。该活动产生的更广泛影响：通过主要研究者对研究生和博士后学生的指导以及参与科罗拉多大学的教学，该研究预计将为感兴趣的公民以及未来科学家的教育和培训做出重大贡献。 ENSO是否会更加积极地应对全球变暖，是社会高度关注的问题。该研究将通过描述控制 ENSO 活动水平的基本力量来帮助解决这个问题。

This study addresses the question of how the level of El Nino-Southern Oscillation (ENSO) activity responds to cooling/warming over the extratropical Pacific. The possibility for a fundamental role of extratropical cooling/warming in determining the level of ENSO activity is raised by recent studies of the role of ENSO in the heat balance of the tropical Pacific. These studies suggest that ENSO acts as a heat pump--a downward and poleward heat transfer mechanism--that regulates the stability of the time-mean state of the coupled tropical ocean/atmosphere. Cooling/warming over the extratropical Pacific can modify the heat balance of the tropical Pacific and perturb the stability of the coupled tropical ocean-atmosphere system through either the "ocean tunnel" or the "atmospheric bridge"--circulations in the atmosphere and in the ocean that connect the tropical region with the extratropical region. The working hypothesis is that an extratropical cooling results in stronger ENSO activity and conversely an extratropical warming weakens ENSO variability. Such extratropical perturbations trigger a response in the level of ENSO activity as ENSO acts as a heat pump that regulates the long-term stability of the equatorial Pacific region. The PIs plan to test this hypothesis by conducting numerical experiments with varying complexity. The intellectual merit of the activity: The research will help to understand global forces controlling the level of ENSO activity, identify causes of variability of ENSO on decadal and longer time-scales, and shed light on the interaction between ENSO and the mean climate. The broader impacts resulting from the activity: Through the principal investigator's supervising graduate and postdoctoral students and participating with teaching in the University of Colorado, the research is expected to contribute significantly to the education and training of interested citizens as well as future scientists. Whether ENSO will become more energetic in response to global warming is an issue of high societal concern. The research will help to address this issue by delineating the fundamental forces controlling the level of ENSO activity.