Studies in the Climate Dynamics of Moist Process Variability and Change

对气候变化的模拟表明，极端降水的发生频率随着气温的升高而增加，这与观测结果大体一致。考虑到温暖的空气通常含有更多的水分，极端的增加是意料之中的。但湿度-温度关系本身并不能提供一个理论来预测气候变暖时极端降水的频率和严重程度的增加。此外，一个令人满意的理论框架将解决各种级别的降水事件发生频率的变化，从微弱到中等再到史无前例的。本奖项的工作旨在通过将对流降水视为一个随机过程并应用统计力学工具(鉴于对流云是最强降水的来源，强调对流降水是合理的)来建立这样的理论框架。其目的是了解给定级别或强度的对流降水事件发生的概率(称为概率分布)如何取决于温度、湿度和其他环境因素。PI和其他人的早期工作表明，当大气湿度增加到与温度相关的阈值(一种散装柱相对湿度的阈值)时，对流降水开始并迅速增强。这里支持的研究扩展了早期的结果，考虑了热力学能量、大气稳定性和柱湿度的概率分布，这些水分对降水中的阈值行为负责。这项工作的一个新颖之处是利用全球降水任务和COSMIC和COSMIC-2卫星上的无线电掩星接收器的配置数据来探索高水分/强降水制度。其他工作使用这些想法来开发对流降水的表示法，用于降水和大气环流相互作用的模型。这项研究的结果被用来评估最先进的气候模型的模拟，试图将当前模拟中的极端降水行为与未来的增加联系起来。如果能够找到可靠的联系，就可以对照相关观测对当前的模拟进行评估，并且可以将模型在再现观察到的联系方面的成功作为基准来评估它们对人为强迫的响应模拟的有效性。由于气温变暖与极端事件频率和严重程度的增加之间的联系，该项目具有社会相关性。对极端降水造成的损害增加的担忧促使人们做出相当大的努力，根据全球气候模型和更高分辨率的区域模型来生成和分析未来的气候模拟。但是，这种“蛮力”方法的结果伴随着很大的不确定性，涉及增加的程度、地理分布和其他特征。因此，一个坚实的理论框架在指导这一努力和解释其结果方面将是非常有价值的。该项目将新理论的发展与其在气候模型行为分析中的应用直接联系起来，从而与气候变化影响评估的更大领域建立了直接联系。此外，该项目为研究生提供支持和培训，工作结果用于开发课堂教材。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。

Simulations of climate change show increases in the frequency of occurrence of extreme precipitation as temperature rises, in general agreement with observations. Increases in extremes are to be expected given that warmer air typically contains more moisture. But the moisture-temperature relationship does not by itself provide a theory to predict increases in the frequency and severity of extreme precipitation in a warming climate. Moreover, a satisfactory theoretical framework would address changes in the frequency of occurrence of precipitation events of all magnitudes, from weak to moderate to unprecedented.Work under this award seeks to develop such a theoretical framework by treating convective precipitation as a random process and applying the tools of statistical mechanics (the emphasis on convective precipitation is reasonable given that convective clouds are the source of most intense precipitation). The goal is to understand how the probability of occurrence of convective precipitation events of a given magnitude or intensity, referred to as the probability distribution, depends on temperature, moisture, and other environmental factors. Earlier work by the PI and others shows initiation and rapid intensification in convective precipitation as atmospheric moisture increases beyond a temperature-dependent threshold, a sort of threshold value of bulk column relative humidity. Research supported here extends earlier results by incorporating considerations of thermodynamic energy, atmospheric stability, and the probability distribution of the column moisture responsible for threshold behavior in precipitation. One novelty of the work is the use of collocated data from the Global Precipitation Mission and Radio Occultation receivers on the COSMIC and COSMIC-2 satellites to explore the high moisture/heavy precipitation regime. Additional work uses these ideas to develop representations of convective precipitation for use in models of the interaction of precipitation and atmospheric circulation. Results of the research are used to evaluate simulations from state-of-the-art climate models, attempting to connect extreme precipitation behaviors in present-day simulations to future increases. If robust connections can be found the present-day simulations can be evaluated against relevant observations, and the success of models in reproducing observed connections can be used as a benchmark to assess the validity of their simulations of the response to anthropogenic forcing.The project has societal relevance due to the connection between warming temperatures and increases in extreme event frequency and severity. Concerns over increasing damage from extreme precipitation have prompted considerable effort in generating and analyzing future climate simulations from global climate models and higher resolution regional models. But results of this "brute force" approach come with substantial uncertainty regarding the degree, geographical distribution, and other characteristics of the increases. A solid theoretical framework would thus be quite valuable in guiding the effort and interpreting its results. This project makes a direct connection between the development of new theory and its application to the analysis of climate model behaviors, thereby establishing an immediate connection to the larger enterprise of climate change impacts assessment. In addition, the project provides support and training for a graduate student, and results of the work are used to develop classroom teaching materials.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.