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)活动水平如何对热带外太平洋变冷/变暖做出反应的问题。最近关于ENSO在热带太平洋热平衡中的作用的研究提出了温带冷却/变暖在确定ENSO活动水平方面发挥基本作用的可能性。这些研究表明，ENSO起到了热泵的作用--一种向下和向极的热量传递机制--调节了热带海洋/大气耦合的时间平均状态的稳定性。温带太平洋上的冷却/变暖可以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大气环流--扰乱热带海洋-大气耦合系统的稳定性。工作假设是，温带降温导致ENSO活动增强，反之，温带变暖导致ENSO变率减弱。这种温带扰动引发了ENSO活动水平的响应，因为ENSO起到了热泵的作用，调节了赤道太平洋区域的长期稳定。PI计划通过进行复杂程度不同的数值实验来检验这一假设。这项活动的学术价值：这项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，并阐明ENSO与平均气候之间的相互作用。活动产生的更广泛的影响：通过首席研究员监督研究生和博士后，并参与科罗拉多大学的教学，预计研究将对感兴趣的公民以及未来的科学家的教育和培训做出重大贡献。ENSO是否会因应全球变暖而变得更有活力，这是一个高度社会关注的问题。这项研究将通过描绘控制ENSO活动水平的基本力量来帮助解决这一问题。

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.