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

这是一个收集和分析智利Chajnantor高原（南纬23度，海拔5100米）阿塔卡马大型毫米波阵列（阿尔马）观测站水汽同位素比和臭氧浓度测量值的项目。 测量结果将用于研究确定亚热带空气团湿度的过程，已知亚热带空气团比热带对流层上部区域更潮湿，它们从那里下降到亚热带。 该地点是进行这些测量的理想地点，因为它是热带对流层顶上部的空气可以一直下降到地球表面而在下降过程中没有实质性变化的少数几个地方之一。 考虑到阿尔马已有的研究基础设施，它也是一个非常方便的站点。测量解决了四个问题：1）水汽和同位素组成在日、季内、季节和年际时间尺度上的协变是什么？2)对流层上层过程是如何设定南半球相对湿度最小值的干燥度的？3)亚热带的湿度在多大程度上受到平流层空气的影响？4)什么过程使副热带相对湿度最低值比热带对流层上部的特定湿度高？臭氧测量被用于解决问题3，因为高臭氧水平可以识别平流层空气的入侵。这些测量将通过一系列诊断活动来补充，以确定水蒸气传输路径，这些路径可以解释观测到的同位素比，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，无论是通过其在水文循环中的作用，还是通过其作为温室气体的辐射效应。这些测量及其分析将加深对水蒸气在大气中循环的途径以及决定干燥地区大气相对湿度的过程的理解，这可能最终提高我们预测天气和预测气候变化的能力。 此外，该项目将在一所有大量西班牙裔和美洲土著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.