CAREER: Understanding Changes in Summertime Continental Temperature Extremes

在一个不断变暖的世界里，预计将出现前所未有的强度和持续时间的热浪，近年来破纪录的热浪证实了这一预期。这类事件发生的频率越来越高，令人担忧，人们自然会担心热浪的严重程度超过了平均气温的上升速度。但是，很难量化最热的日子比平均气温上升更快的程度，即使最热的日子以与其他所有日子相同的速度变暖，热浪也会变得更加严重。一个挑战是，从定义上讲，极端高温是罕见的，因此样本数量有限，无法得出统计上可靠的结论。样本量问题尤其具有挑战性，因为最热的天气变暖速度在多大程度上可能因地区而异。进一步的挑战是，我们对可能导致炎热天气比平均天气更强的变暖趋势的物理机制没有令人满意的了解。在这个奖项下的工作涉及在最热的日子里温度上升的程度和可能负责的物理机制。温度趋势分析在区域基础上比较温度分布的第50百分位和第95百分位的趋势，并使用各种统计方法克服样本量限制并考虑自然变率。该分析还考虑了气候模式比对项目（CMIP）和社区地球系统模式（CESM）创建的大集合的模拟结果。研究物理机制的工作重点是土壤干燥在多大程度上导致极端温度，特别是干燥伴随着热浪，干燥限制了地表通过蒸发和蒸腾作用降温的程度，从而导致更大的变暖。通过将地表能量平衡方程应用于观测和模式输出，并通过CESM的理想实验，探讨了极端温度对土壤湿度和蒸散的依赖关系。该CAREER提案的教育部分旨在建立气候和数据科学之间的桥梁，以促进两个领域之间更有效的合作。其中一项活动是为大一的环境科学课程开发一个教育模块，旨在通过动手数据分析来教授统计思维。该模块使用jupypiter笔记本，让学生可以访问自己家乡的观测数据，并指导他们计算平均值和极值及其随时间的变化。另一项活动是在美国国家大气研究中心（NCAR）为30-40名研究数据科学与气候科学的研究生举办的研讨会。该研讨会主要致力于“科学黑客马拉松”，由不同学科背景的学生组成的团队将共同努力解决与极端气候有关的具体问题。该奖项为通过公开竞争程序选出的20名研讨会参与者提供支持。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。

Heat waves of unprecedented intensity and duration are expected in a warming world, and the record-breaking heat waves of recent years confirm this expectation. The increasing frequency of such events is alarming and naturally leads to concerns that the severity of heat waves is outpacing the rise in mean temperature. But the extent to which the hottest days are warming faster than the average temperature increase is hard to quantify, and certainly heat waves would become more severe even if the hottest days warmed at the same rate as all the other days. One challenge is that heat extremes are rare by definition, thus there is limited sample size to make statistically robust conclusions. The sample size issue is particularly challenging as the extent to which the hottest days warm faster is likely to vary from one region to another. A further challenge is that we do not have a satisfactory understanding of the physical mechanisms that might lead to stronger warming trends for hot days than for average days.Work under this award addresses both the extent to which temperature increases are greater for the hottest days and the physical mechanisms the might be responsible. The analysis of temperature trends compares trends for the 50th and 95th percentiles of the temperature distribution on a regional basis and uses various statistical methods to overcome sample size limitations and account for natural variability. The analysis also considers output from the simulations available from the Climate Model Intercomparison Project (CMIP) and the Large Ensembles created with the Community Earth System Model (CESM). Work addressing physical mechanisms focuses the extent to which drying of the soil contributes to temperature extremes, in particular that drying accompanies heat waves and drying limits the extent to which the surface can cool through evaporation and transpiration, thus leading to greater warming. The dependence of temperature extremes on soil moisture and evapotranspiration is explored by applying a surface energy budget equation to observations and model output, and through idealized experiments with CESM.The educational component of this CAREER proposal seeks to build a bridge between climate and data science to foster more effective collaboration between the two fields. One activity is the development of an educational module for a freshman class in environmental science intended to teach statistical thinking through hands-on data analysis. The module uses Juypiter notebooks to give students access to observational data for their own hometowns, and guides them through the calculation of means and extremes and their variation over time. Another activity is a workshop for 30-40 graduate students working at the interface between data science and climate science, to be held at the National Center for Atmospheric Research (NCAR). The workshop is mostly devoted to a 'science hackathon' in which teams of students with a mix of disciplinary backgrounds will work together to solve specific problems related to climate extremes. The award provides support for 20 attendees at the workshop who are chosen through an open competitive process.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.