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

本研究探讨了厄尔尼诺-南方涛动（ENSO）活动水平如何对热带太平洋外的变冷/变暖作出响应。最近关于ENSO在热带太平洋热量平衡中的作用的研究提出了热带外冷却/变暖在确定ENSO活动水平方面的基本作用的可能性。这些研究表明，厄尔尼诺/南方涛动起着热泵的作用-一种向下和向极的热传递机制-调节热带海洋/大气耦合的时间平均状态的稳定性。热带外太平洋的变冷/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”-连接热带地区和热带外地区的大气和海洋环流-扰动热带海洋-大气耦合系统的稳定性。工作假设是，一个外热带冷却的结果在更强的ENSO活动，相反，一个外热带变暖削弱ENSO的变化。 由于厄尔尼诺/南方涛动起着调节赤道太平洋区域长期稳定性的热泵作用，这种热带外扰动引发了厄尔尼诺/南方涛动活动水平的反应。PI计划通过进行不同复杂度的数值实验来测试这一假设。这项活动的学术价值：这项研究将有助于了解控制厄尔尼诺/南方涛动活动水平的全球力量，查明厄尔尼诺/南方涛动在十年和更长时间尺度上的变化原因，并阐明厄尔尼诺/南方涛动与平均气候之间的相互作用。活动产生的更广泛的影响：通过主要研究者的监督研究生和博士后学生，并参与科罗拉多大学的教学，研究预计将大大有助于教育和培训感兴趣的公民以及未来的科学家。ENSO是否会对全球变暖作出更有力的反应是一个社会高度关注的问题。这项研究将有助于解决这一问题，划定控制厄尔尼诺/南方涛动活动水平的基本力量。

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.