Studies in the Climate Dynamics of Moist Process Variability and Change

气候变化模拟表明，随着温度升高，极端降水的发生频率增加，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，预计极端天气会增加。但是，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处理各种量级降水事件发生频率的变化，从弱到中等到前所未有。该奖项下的工作旨在通过将对流降水视为随机过程并应用统计力学工具来发展这样一个理论框架（考虑到对流云是大多数强降水的来源，强调对流降水是合理的）。目的是了解给定量级或强度的对流降水事件发生的概率（即概率分布）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，当大气湿度增加超过与温度相关的阈值时，对流降水的开始和迅速加强，这是一种整体柱相对湿度的阈值。这里支持的研究扩展了早期的结果，纳入了热力学能量、大气稳定性和降水中负责阈值行为的柱湿度概率分布的考虑。这项工作的一个新颖之处在于使用来自全球降水任务和COSMIC和COSMIC-2卫星上的无线电掩星接收器的并发数据来探索高湿度/强降水状态。进一步的工作利用这些思想发展对流降水的表示，用于降水和大气环流相互作用的模式。研究结果被用于评估最先进的气候模式的模拟，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。如果能找到可靠的联系，就可以根据相关观测来评估当前的模拟，而模式在再现观测到的联系方面的成功，可以用作评估其对人为强迫响应的模拟有效性的基准。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。对极端降水造成的日益严重的破坏的担忧促使人们在利用全球气候模式和更高分辨率的区域模式生成和分析未来气候模拟方面付出了相当大的努力。但是，这种“蛮力”方法的结果在程度、地理分布和其他增长特征方面具有很大的不确定性。因此，一个坚实的理论框架在指导这项工作和解释其结果方面是非常有价值的。本项目将新理论的发展与其在气候模式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这一更大的事业建立了直接的联系。此外，该项目还为研究生提供支持和培训，并将工作成果用于开发课堂教材。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。

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.