Aerosol Pollution Impacts on Wintertime Orographic Precipitation

本项目旨在增进对气溶胶污染对冬季地形降水的潜在影响的了解，并由此扩展到水资源。研究最初将集中在科罗拉多州的落基山脉，但最终将寻求了解这些结果在其他地区（如内华达山脉）的潜在普遍性。需要解决的一个关键问题是，是否存在这样一种状态，即云底温度足够高，使得气溶胶污染的增加能够抑制毛毛雨，从而相应增加过冷云中液态水的含量，并最终增强（相对于抑制）降水。这项工作的智力价值在于利用科罗拉多州立大学RAMS中尺度模型进行精心规划的数值研究，该模型将利用并扩展由首席研究员和同事在科罗拉多公园山脉进行的先前观测工作，以及最近NSF和能源部在同一地区支持的其他研究。这些先前的数据将用于改进对输送到科罗拉多州西部的气溶胶污染范围的估计，改进RAMS模型中的微物理表示，评估模型的性能，并最终改进气溶胶污染对科罗拉多州冬季总降水影响的定量估计。检验对云底温度的敏感性以及气溶胶对降水影响迹象可能逆转的证据（即增强与抑制）的试验，可能与内华达山脉等较暖的山脉特别相关。更广泛的影响将包括研究生教育，增强RAMS模型的能力，更好地理解人口对区域气候的相互交织的影响，以及管理积雪源供水的最佳实践，这对美国西部山区不断增长的人口至关重要

This project seeks to increase understanding of potential influences of aerosol pollution on wintertime orographic precipitation and, by extension, water resources. Research will initially focus on the Rocky Mountains of Colorado, but will ultimately seek to understand potential generality of these results in other regions such as the Sierra Nevada. A key question to be addressed is whether there is a regime in which cloud base temperatures are warm enough so that increased aerosol pollution can lead to suppression of drizzle, corresponding increase in supercooled cloud liquid water content, and ultimately an enhancement (vs. suppression) of precipitation. The intellectual merit of this work rests in conducting carefully planned numerical studies utilizing the Colorado State University RAMS mesoscale model that will both capitalize on and extend prior observational work undertaken by the principal investigator and colleagues over the Park Range of Colorado, as well as other recent NSF and Department of Energy supported studies in this same region. These prior data will be used to refine estimates of the range of aerosol pollution transported into western Colorado, make improvements to microphysical representations within the RAMS model, evaluate the model's performance, and ultimately to make improved quantitative estimates of aerosol pollution impacts on winter-season total precipitation in Colorado. Tests examining sensitivity to cloud base temperature and evidence for the potential reversal of the sign of aerosol impacts on precipitation (viz. enhancement vs. suppression) may have particular relevance to warmer-based mountain ranges such as the Sierra Nevada range. Broader impacts will include graduate student education, enhanced capabilities for the RAMS model, and better understanding of intertwined demographic impacts on regional climate and best practices for management of snowpack-derived water supplies that are of key importance to growing populations bordering mountainous regions across the western U.S.