Continuing Measurements of Water Vapor, Clouds, Aerosol, and Waves Above, and Across, the Tropical Tropopause Layer with in Situ Instruments on Circum-Tropical Isopycnic Balloons

该奖项支持首席调查人员继续参加由法国国家空间研究中心(CNES)和巴黎萨克雷大学动力气象学实验室(LMD)组织的Strateole-2实地活动。该活动利用气球观测热带对流层顶层(TTL)，即热带对流层和平流层之间大约14公里到18公里的大气层，气球设计用于长达3个月的飞行，在恒定高度漂浮。这些气球从塞舌尔群岛发射升空，在TTL顶部(近18公里)围绕赤道漂浮，或在接近20公里的平流层下部漂浮。Strateole-2计划为三次部署，一次是8次气球飞行的初步工程部署，然后是两次每次20次飞行的科学部署。前两次部署是在2019年和2021年进行的，通过AGS-1643022提供了警察参与这些部署的资金。这里提供的资金用于支持参加计划于2025年10月开始的第三次活动。该奖项的主要任务是生产气球携带的仪器，以观测温度、湿度、气溶胶和卷云冰粒。其中一种仪器是LASP粒子计数器(LPC)，以科罗拉多博尔德大学大气和空间物理实验室的名字命名。LPC在气球吊车上飞行，使用激光后向散射探测气溶胶和冰粒。它可以在32个大小的垃圾桶中测定0.3到30微米的颗粒浓度。LPC配有为天气气球开发的湿度和温度传感器Vaisala RS41，它可以检测TTL和平流层下部发现的低湿度时的湿度。在2025年的部署中，将发射五个LPC，其中三个在18公里处，两个在20公里处。第二个仪器是Reeldown气溶胶、云、湿度和温度传感器(RACHuTS)，它是一个2公斤重的包裹，用绳子上下缠绕，产生气球下方2公里的探测信号。RACHuTS将热力学传感器(TSEN，由法国团队开发)与名为ROPC(RACHuTS光学颗粒计数器，有8个尺寸从0.3到10微米的8个料箱)的较小版本的LPC集成在一起，以及RS41型和根据AGS-2233136开发的可调谐二极管激光器水分传感器。TDL是对之前部署中使用的Flash-B湿度传感器的改进，因为它对环境光不敏感，因此可以在白天使用，使分析的机会翻了一番。RACHuTS以一米的垂直分辨率制作轮廓，当它下降时，一个轮廓，当它返回座舱时，另一个轮廓。三台RACHuTS剖面仪将在2025年部署，全部在18公里处飞行。与早期部署一样，使用LPC和RACHuTS进行的测量将用于解决TTL科学中的三个问题。首先是过饱和在多大程度上是决定平流层湿度的重要因素。在假设相对湿度达到100%时发生水蒸气凝结或沉积的假设下，平流层湿度被认为受到空气在最冷温度下遇到的饱和水汽压的限制，因为它通过TTL进入平流层。但之前部署的数据显示，相对湿度超过150%，这表明冷点饱和蒸汽压可能不像之前假设的那样严格。一个相关的问题是大气波在TTL卷云形成中的作用，因为之前的RACHuTS部署和其他证据表明，TTL内的大多数冰粒层是由与波浪运动上升相关的冷却产生的。这些层可能很薄，可能只有10米，因此RACHuTS剖面的一米分辨率是观察这些层所必需的。该项目要解决的第三个问题是发现大颗粒层，大小从2微米到20微米不等，相对湿度太低，不能形成冰。这些粒子的性质还有待确定。研究它们的一种策略是在20公里高度的两个气球上飞行LPC，气球位于TTL上方，通常过于温暖和干燥，无法支撑冰云。超微米粒子的探测将有力地证明这些粒子不是由普通冰组成的。由于要收集的独特数据集，特别是采样时间长、垂直分辨率高和观测质量高，这项工作具有科学上更广泛的影响。RACHuTS和LPC观测结果将免费提供给研究界，以便它们可以以这里没有预料到的方式使用。此外，该项目还开发了气象观测的新技术，这些技术可能会有广泛的科学应用。除了这些考虑之外，该项目还支持一名博士后研究助理，从而培养这一研究领域未来的科学队伍。该项目开展了大量的国际合作，并为科罗拉多大学的一名研究科学家和一名本科生提供支持和培训。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。

This award supports the continued participation of the Principal Investigators (PIs) in the Strateole-2 field campaign, organized by the French space agency (CNES, for Centre National d'Etudes Spatiales) and the Laboratory for Dynamic Meteorology (LMD) at the University of Paris-Saclay. The campaign makes observations of the tropical tropopause layer (TTL), the layer of the atmosphere from roughly 14km to 18km between the tropical troposphere and stratosphere, using balloons designed to float at a constant altitude for flights of up to 3 months. The balloons are launched from the Seychelles and float around the equator at the top of the TTL (near 18km) or in the lower stratosphere at an altitude close to 20km. Strateole-2 was planned as a set of three deployments, a preliminary engineering deployment with 8 balloon flights followed by two science deployments with 20 flights each. The first two deployments took place in 2019 and 2021 and funds for the PIs' participation in these deployments were provided through AGS-1643022. Funds provided here support participation in the third campaign, scheduled to begin in October 2025.The primary task under this award is the production of balloon-borne instruments to observe temperature, moisture, aerosols, and cirrus cloud ice particles. One instrument is the LASP Particle Counter (LPC), named for the Laboratory for Atmospheric and Space Physics at the University of Colorado Boulder. The LPC flies on the balloon gondola and detects aerosols and ice particles using laser backscatter. It can determine the concentration of particles of sizes ranging from 0.3 to 30 microns in 32 size bins. The LPC is accompanied by a moisture and temperature sensor developed for use in weather balloons, the Vaisala RS41, which can detect moisture at the low humidities found in the TTL and lower stratosphere. Five LPCs will be flown in the 2025 deployment, three at 18km and two at 20km.A second instrument is the Reeldown Aerosol, Cloud, Humidity and Temperature Sensor (RACHuTS), a 2kg package which is reeled up and down on a cord to generate soundings extending 2km below the balloon. RACHuTS integrates the Thermodynamic SENsor (TSEN, developed by a French team) with a smaller version of the LPC called the ROPC (RACHuTS Optical Particle Counter, with 8 size bins from 0.3 to 10 microns), along with an RS41 and the Tunable Diode Laser (TDL) moisture sensor developed under AGS-2233136. TDL is an improvement over the FLASH-B moisture sensor used in the previous deployments since it is not sensitive to ambient light and can thus be used during the day, doubling the opportunities for profiling. RACHuTS makes profiles with one meter vertical resolution, with one profile as it descends and another as it returns to the gondola. Three RACHuTS profilers will be flown in the 2025 deployment, all at 18km.As in the earlier deployments the measurements taken using LPC and RACHuTS will be used to address three issues in TTL science. The first is the extent to which supersaturation is an important factor in determining humidity in the stratosphere. Stratospheric humidity is thought to be limited by the saturation vapor pressure at the coldest temperature air encounters as it rises through the TTL to enter the stratosphere, under the assumption that water vapor condensation or deposition occurs when relative humidity reaches 100%. But data from previous deployments shows relative humidities above 150%, suggesting that the cold point saturation vapor pressure may not be as strict a limit as previously supposed. A related issue is the role of atmospheric waves in the formation of cirrus clouds in the TTL, as previous RACHuTS deployments and other evidence suggests that the majority of ice particle layers within the TTL are generated by cooling associated with rising motions in waves. The layers can be quite thin, perhaps only 10 meters, thus the one meter resolution of RACHuTS profiles is necessary to observe the layers. The third issue to be addressed in the project is the finding of layers of large particles, in the size range from 2 to 20 microns, at relative humidities too low to allow ice formation. The nature of these particles has yet to be determined. One strategy for studying them is to fly the LPC on two balloons at the 20km level, which is above the TTL and typically too warm and dry to support ice clouds. The detection of super-micron particles at that level would be a strong argument that the particles are not composed of ordinary ice.The work has scientific broader impacts due to the unique dataset to be collected, in particular the long sampling time, high vertical resolution, and high quality of the observations. RACHuTS and LPC observations will be made freely available to the research community so that they can be used in ways not anticipated here. In addition, the project develops novel technologies for meteorological observations that could have a wide array of scientific applications. Beyond these considerations, the project supports a postdoctoral research associate, thereby developing the future scientific workforce in this research area. The project develops a substantial international collaboration and also provides support and training to a research scientist and an undergraduate student at the University of Colorado.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.