Water Vapor Isotopic Measurements on the Chajnantor Plateau, Chile and Implications for Subtropical Humidity Dynamics

这是一个项目，旨在收集和分析智利查南托高原(北纬23度，海拔5100米)上阿塔卡马大毫米阵列(ALMA)天文台现场的水蒸气同位素比和臭氧浓度测量结果。这些测量将被用于研究决定副热带气团湿度的过程，众所周知，副热带气团比热带对流层上层地区更潮湿，它们从那里下降到亚热带地区。该地点是进行这些测量的理想地点之一，因为它是少数几个从热带高层对流层顶空气可以一路下降到地球表面的地方之一，在下降过程中不需要进行实质性的修改。考虑到ALMA的研究基础设施已经到位，它也是一个非常方便的地点。测量解决了四个问题：1)在每日、季节内、季节和年际时间尺度上，水汽和同位素组成的协变性是什么？2)高层对流层过程如何将南半球的干旱相对湿度设定为最小？3)平流层空气的侵入对副热带相对湿度的影响有多大？4)什么过程使副热带相对湿度最小到高于热带对流层上层遇到的特定湿度？臭氧测量被用来解决问题3，因为高臭氧水平可以识别平流层空气的侵入。这些测量将得到一套确定水蒸气传输路径的对角化活动的补充，这些路径解释了观测到的同位素比率、比湿度和臭氧浓度。由于水蒸气在大气中的重要性，这项工作具有更广泛的影响，既通过它在水文循环中的作用，也通过它作为温室气体的辐射效应。这些测量及其分析将使我们更好地了解水蒸气在大气中循环的途径，以及决定干旱地区大气相对湿度的过程，这最终可能会提高我们预测天气和预测气候变化的能力。此外，该项目将在一所拥有大量拉美裔和美洲原住民学生的大学教育和培训一名研究生。

This is a project to collect and analyze measurements of water vapor isotope ratios and ozone concentrations at the site of the Atacama Large Millimeter Array (ALMA) observatory on the Chajnantor Plateau in Chile (23S latitude, elevation 5100m). The measurements will be used to study the processes which determine the humidity of subtropical air masses, which are known to be more moist than region of the tropical upper troposphere from which they descend into the subtropics. The site is ideal for making these measurements because it is one of the few places where air from the tropical upper tropopause can descend all the way to the Earth's surface without substantial modification during descent. It is also an extremely convenient site given the research infrastructure already in place for ALMA.The measurements address four questions: 1) What is the co-variability of water vapor and isotopic composition on daily, intraseasonal, seasonal, and interannual time scales? 2) How do upper tropospheric processes set the aridity of the Southern Hemisphere relative humidity minimum? 3) To what extent is subtropical humidity influenced by instrusions of stratospheric air? 4) What processes moisten the subtropical RH minimum to specific humidities above those encountered in the tropical upper troposphere? Ozone measurements are used to address question 3, as high ozone levels can identify intrusions of stratospheric air. The measurements will be complemented by a suite of diagonstic activities to identify water vapor transport pathways that account for the observed isotope ratios, specific humidity, and ozone concentration.The work has broader impacts due to the importance of water vapor in the atmosphere, both through its role in the hydrological cycle and through its radiative effect as a greenhouse gas. The measurements and their analysis will provide increased understanding of the pathways through which water vapor circulates in the atmosphere, and the processes which determine atmospheric relative humidity in dry regions, which may ultimately improve our ability to forecast weather and anticipate climate change. In addition, the project will educate and train a graduate student at a university with a substantial Hispanic and Native American student population.