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

大尺度大气环流的特征是绕极流，绕着分布在地球仪上的高压和低压中心航行。这种循环随时间而变化，从几天到几十年不等。当在一个季节中平均时，气候环流特征在地理上是固定的，表现为振幅恒定的驻波。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组成的（即，异常）。这种反复出现和持续存在的异常模式被称为遥相关模式。它们可以自然地作为我们混乱的大气系统的一部分出现，并且可以被异常温暖的海洋表面持续的区域加热等事件所激发。遥相关模式和伴随而来的驻波之间的干扰可以加强高压和低压中心，导致极端天气和气候事件，如干旱和洪水以及不合季节的寒冷和温暖。近几十年来，夏季极端事件的发生有所增加，其对全球变暖的归因尚不清楚。迄今为止，激发和维持夏季遥相关模式背后的机制还没有得到很好的理解。该建议旨在了解激发与极端表面温度特征相关的夏季遥相关模式的物理机制。研究人员假设，热浪频率的年代际增加与北方夏季特定遥相关模式（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表面温度的可能影响。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）变化，如果有，探索这些长期变化的可能原因。研究方法包括对流层上部位势高度和地表气温场的组合聚类分析、对结果聚类模式的各种诊断分析、地表能量收支分析和数值模拟。该奖项反映了NSF的法定使命，并通过使用基金会的知识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 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.