CAREER: Understanding Changes in Summertime Continental Temperature Extremes

在一个变暖的世界里，预计会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。这类事件的频率越来越高令人担忧，自然会引发人们的担忧，即热浪的严重程度正在超过平均气温的上升。但最热的日子变暖的速度快于平均气温上升的程度很难量化，而且可以肯定的是，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，根据定义，极端高温是罕见的，因此做出统计上可靠的结论的样本量有限。样本量问题尤其具有挑战性，因为最热的日子变暖的速度可能会因地区而异。另一个挑战是，我们对可能导致炎热天气比平日更强烈变暖趋势的物理机制没有令人满意的理解。该奖项下的工作既解决了最热日子气温上升幅度更大的问题，也解决了可能对此负责的物理机制。温度趋势分析比较了区域温度分布的第50和第95百分位数的趋势，并使用各种统计方法来克服样本量限制并考虑自然变异性。分析还考虑了气候模型比较项目(CMIP)和利用共同体地球系统模型(CESM)创建的大型集合所提供的模拟的输出。关于物理机制的研究集中于土壤干燥导致极端温度的程度，特别是干燥伴随着热浪，干燥限制了表面通过蒸发和蒸腾冷却的程度，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型输出，以及通过与CESM的理想化实验，探索了极端温度对土壤水分和蒸散量的依赖关系。这一职业提案的教育部分寻求在气候和数据科学之间建立一座桥梁，以促进这两个领域之间更有效的合作。其中一项活动是为环境科学的一年级班级开发一个教育模块，旨在通过实际操作的数据分析教授统计思维。该模块使用Juypiter笔记本让学生访问他们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。另一项活动是在国家大气研究中心(NCAR)为30-40名从事数据科学和气候科学之间的工作的研究生举办的讲习班。研讨会的主要内容是科学黑客松，来自不同学科背景的学生团队将共同解决与极端气候有关的具体问题。该奖项为研讨会上通过公开竞争程序选出的20名与会者提供支持。该奖项反映了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。

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.