The factors governing daily near-surface air temperature variability over land

地表气温的极端高温和极端低温与大气环流模式有明显的联系，例如，美国大陆最冷的温度与极地锋后向南流动的空气有关，而夏季热浪与停滞的高压系统有关。但是，虽然从天气图上可以明显看出大气环流的影响，但下面的陆地表面也会影响冷热事件的严重程度。例如，在热浪期间，如果土壤是湿的，由于蒸发冷却，最高地表空气温度可能会降低，因此土壤湿度可以在限制温度波动幅度方面发挥重要作用。其他表面特性，包括积雪、反射率和表面粗糙度，被认为会影响地表气温的变化，但这些特性的影响程度难以量化。该项目考察了大气环流和陆地表面特性对地表气温变化的影响，试图确定1)仅靠大尺度大气环流就能解释的温度变化比例，以及这一比例如何随地点和季节而变化；(2)控制大尺度大气环流后地表对地表气温影响的关键途径；3)地表对极端事件强度的影响程度，以及对亚季节或季节可预测性的影响程度。pi使用统计方法生成最适合的地表气温模式，仅基于高空大气环流，然后将这些由环流得出的温度模式的统计数据与实际温度统计数据进行比较，以确定两者差异暗示地表特性起重要作用的地区和季节。在观测分析之后，进行了一系列模式的数值实验，以了解地表影响温度变化的物理机制。模型层次包括社区大气模型（CAM）和简单陆地界面模型（SLIM），后者是一种陆地表面模型，可以直接控制重要的陆地表面特性。利用CAM-SLIM和其他模式配置进行的敏感性研究结果应用于对北美、欧洲和澳大利亚最近的热浪的分析。极端温度对人类福祉有许多影响，如死亡率、作物损失和基础设施故障。更好地了解陆地表面性质在确定这些极端事件的严重程度方面所起的作用，可能有助于预测它们的发生，以及它们的频率和强度可能受到气候变化影响的程度。这项工作还将通过开发和传播SLIM使更广泛的科学界受益，SLIM将作为社区地球系统模型公开发布的一部分提供。该项目还包括通过大气研究与科学重大机遇（SOARS）计划进行教育和推广，并支持一名研究生和一名博士后研究助理。该奖项反映了美国国家科学基金会的法定使命，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。

Hot and and cold extremes of surface air temperature have a clear association with atmospheric circulation patterns, for instance the coldest temperatures over the continental US are associated with the southward flow of air behind the polar front while summer heat waves are associated with stalled high pressure systems. But while the influence of atmospheric circulation is evident from weather maps, the underlying land surface can also affect the severity of hot and cold events. For instance the maximum surface air temperature during a heat wave could be lower due to evaporative cooling if the soil is wet, thus soil moisture could play an important role in limiting the magnitude of temperature fluctuations. Other surface properties including snow cover, reflectivity, and surface roughness are thought to influence surface air temperature variability, but the extent of the influence of these properties is difficult to quantify.This project examines the effects of atmospheric circulation and land surface properties on surface air temperature variability, seeking to determine 1) the fraction of temperature variability that can be explained by the large-scale atmospheric circulation alone, and how this varies as a function of location and season; 2) the key pathways through which the land surface can influence surface air temperature after controlling for the large-scale atmospheric circulation; and 3) the extent to which the land surface can modify the magnitude of extreme events, and may allow for subseasonal to seasonal predictability. The PIs use statistical methods to generate best-fit surface air temperature patterns based solely on the atmospheric circulation aloft, then compare the statistics of these circulation-derived temperature patterns to the actual temperature statistics to identify regions and seasons where differences in the two imply a strong role for surface properties. This observational analysis is followed by numerical experiments with a hierarchy of models to understand the physical mechanisms through which the land surface affects temperature variations. The model hierarchy includes the Community Atmosphere Model (CAM) coupled to the Simple Land Interface Model (SLIM), a land surface model configured to allows direct control of important land surface properties. Results of sensitivity studies carried out with CAM-SLIM and other model configurations are applied to the analysis of recent heat waves in North America, Europe, and Australia.Temperature extremes have numerous effects on human well being through impacts such as mortality, crop losses, and infrastructure failure. Better understanding of the role played by land surface properties in determining the severity of these extremes could prove useful in anticipating their occurrence, and the extent to which their frequency and intensity may be affected by climate change. The work will also benefit the broader scientific community through the development and dissemination of SLIM, which will be made available as part of a public release of the Community Earth System Model. The project also includes education and outreach through the Significant Opportunities in Atmospheric Research and Science (SOARS) program, and supports a graduate student and a postdoctoral research associate.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.