The Mechanisms that Drive Summer Teleconnections: Patterns Associated with High Surface Temperatures

大尺度大气环流的特点是绕极气流绕过分布在全球各地的高、低压中心。这种循环在时间上是不同的，从几天到几十年不等。当在一个季节平均时，气候环流特征在地理上看起来固定为恒定幅度的驻波。在一个季节内，大尺度大气环流可以被认为是由这些驻波和偏离它们的演变模式(即异常)组成的。反复出现的和持续的异常模式被称为遥相关模式。它们可以自然地出现在我们混乱的大气系统中，并可能被异常温暖的海洋表面上持续的区域加热等事件所激发。遥相关型和随之而来的静止波之间的干扰可能会加剧高压和低压中心，导致极端天气和气候事件，如干旱和洪水，以及反常的寒冷和温暖时期。近几十年来，夏季极端事件的发生有所增加，其全球变暖的原因尚不清楚。到目前为止，夏季遥相关型激发和维持背后的机制还不是很清楚。这项提议旨在了解激发夏季遥相关模式的物理机制，这些模式与极端地表温度特征有关。研究人员假设，热浪频率的年代际增加与北方夏季特殊遥相关模式(由非绝热加热引发)的增加相吻合。研究人员计划研究这些遥相关和驻波之间的干扰对地表温度的可能影响。他们将评估夏季遥相关模式的频率和强度是否有任何长期(超过十年)的变化，如果是，则探索这些长期变化的可能原因。研究方法包括组合高层对流层位势高度和地面气温场的集群分析，对由此产生的集群模式的各种诊断分析，地表能量收支分析，以及数值模拟。这一奖项反映了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。

The large-scale atmospheric circulation is characterized by circumpolar flows that navigate around high- and low-pressure centers distributed across the globe. This circulation varies in time, ranging from a few days to well over decades. When averaged over a season, the climatological circulation features appear fixed geographically as stationary waves of constant amplitudes. Within a season, the large-scale atmospheric circulation can be thought of as comprising of these stationary waves and evolving patterns that deviate from them (i.e., anomalies). The recurring and persistent anomalous patterns are referred to as teleconnection patterns. They can appear naturally as a part of our chaotic atmospheric system and can be excited by events like sustained regional heating over the unusually warm ocean surface. The interference between teleconnection patterns and the attendant stationary waves can intensify high- and low-pressure centers leading to extreme weather and climate events such as droughts and floods as well as unseasonably cold and warm spells. In recent decades, the occurrence of summertime extreme events has increased and its attribution to global warming is unclear. To date, the mechanisms behind the excitation and maintenance of the summertime teleconnection patterns are not well understood. This proposal aims to understand the physical mechanisms that excite summer teleconnection patterns associated with extreme surface temperature signatures. The investigators hypothesize that the inter-decadal increase in the heat wave frequency has coincided with an increased occurrence of particular teleconnection patterns (initiated by diabatic heating) during the boreal summer. The investigators plan to examine the possible impact of interference between these teleconnections and stationary waves on surface temperature. They will assess if there has been any long term (greater than a decade) changes in the frequency and intensity of the summer teleconnection patterns and, if so, explore possible causes of these long-term changes. The research methods include cluster analysis of the combined upper tropospheric geopotential height and surface air temperature fields, various diagnostic analyses of the resulting cluster patterns, surface energy budget analysis, and numerical modeling.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.