Collaborative Research: Four-Dimensional (4D) Investigation of Tropical Waves Using High-Resolution GNSS Radio Occultation from Strateole2 Balloons

该奖项支持主要研究人员继续参与由法国航天局（CNES，国家空间研究中心）和巴黎萨克雷大学动态气象实验室组织的“战略-2”实地活动。该活动使用设计为在恒定高度漂浮长达3个月的气球，对热带对流层顶层（TTL）进行观测，TTL是热带对流层和平流层之间大约14公里至18公里的大气层层。这些气球从塞舌尔发射，漂浮在赤道附近的TTL顶部（18公里）或平流层下部（20公里）。stratole -2计划分为三次部署，一次是初步的工程部署，有8次气球飞行，然后是两次科学部署，每次飞行20次。前两次部署分别于2019年和2021年进行，pi使用AGS-1642650和AGS-1642644的资金参与了这些部署。ppi参与计划于2025年10月开始的第三次部署，得到了这里的支持。pi在战略-2中的作用是建造和飞行一个名为ROC的无线电掩星接收器，它可以探测全球导航卫星系统（GNSS，其中包括美国发射的GPS卫星）卫星发射的无线电波的折射。折射的强度可以用来推断ROC和发射卫星之间的视线沿线的大气温度，因此ROC可以通过跟踪GNSS卫星，当它下降到地平线或从地平线以下上升时，来创建温度剖面。该合同的资金将用于建造6台ROC接收器，管理其现场部署，并收集和分析其生成的数据。ROC的温度剖面很有趣，因为它们显示了与大面积热带对流产生的TTL波动相关的温度波动。这些波引起人们兴趣的一个原因是，它们驱动了准两年一次的振荡（QBO），即赤道平流层东西风的交替，从平流层上层开始，下降到对流层顶，大约持续两年。QBO只限于热带地区，但它影响着世界各地的天气和气候。众所周知，QBO是由由TTL向上传播的波的垂直动量通量驱动的，但尚不清楚哪种类型的波，特别是在波长和频率方面，对驱动QBO最重要。另一个引起人们兴趣的原因是，波浪的上下运动与周围空气的冷却和变暖有关，而上升运动引起的冷却会导致水蒸气冻结成冰粒（这一过程称为沉积）。冰的形成很重要，因为它使进入平流层的空气脱水，从而调节平流层的湿度，还因为冰粒形成卷云，通过捕获向外的红外辐射来影响地球的气候。QBO的波浪驱动工作侧重于周期为3或4天的波浪，这在以前的部署中被发现是突出的。pi试图确定波的三维结构及其固有频率，这些因素共同决定了它们的波动量通量，从而确定了它们对QBO驱动的潜在重要性。pi已经开发了探测波结构的技术，利用RO剖面从气球侧面看的事实，并在距离气球吊舱的距离较低的连续高度测量温度。因此，可以通过结合沿气球飞行路径的连续RO剖面来重建波的三维结构。至于卷云的形成，六个ROC接收器中的四个将使用一个向下指向的激光雷达，称为BeCOOL，气球载云超调观测激光雷达（BeCOOL），由一个法国团队开发。卷云的BeCOOL观测可以与波浪引起的温度波动的ROC观测相结合，以确定卷云在TTL波的冷相中发生的程度。这项工作通过与天气预报的联系而具有社会价值。卫星上的无线电掩星接收器是业务天气预报中使用的观测资料的重要来源，这里进行的工作包括将ROC观测资料吸收到天气模型中并测试其预测价值。数据同化和预测工作涉及与两个操作中心的协作。此外，天气模式难以模拟QBO及其全球影响，因此更好地了解QBO的波驱动有助于更好的预报模式。该活动的所有数据都免费提供给全球研究界，并可以以各种方式使用，超出了该活动的目标。该项目还通过支持两名研究生和为本科生（包括两名来自塞舌尔的学生）提供实习机会来建设科研队伍。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。

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 Dynamic Meteorology Laboratory 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 (18km) or in the lower stratosphere (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 the PIs participated in these deployments using funds from AGS-1642650 and AGS-1642644. The PIs' participation in the third deployment, scheduled to begin in October 2025, is supported here.The PIs' role in Strateole-2 is to build and fly a Radio OCcultation receiver called ROC, which detects the refraction of radio waves transmitted by satellites from the Global Navigation Satellite System (GNSS, which includes the GPS satellites launched by the US). The strength of the refraction can be used to infer atmospheric temperature along the line of sight between ROC and a transmitter satellite, thus ROC can create temperature profiles by tracking a GNSS satellite as it descends to the horizon or rises from below it. Funds from this award are used to build six ROC receivers, manage their field deployment, and collect and analyze the data they generate.The temperature profiles from ROC are of interest because they show temperature fluctuations associated with wave motions in the TTL generated by large areas of tropical convection. One reason these waves are of interest is that they drive the quasi-biennial oscillation (QBO), an alternation between eastward and westward winds in the equatorial stratosphere which begins in the upper stratosphere and descends to the tropopause over the course of roughly two years. The QBO is confined to the tropics but it affects weather and climate around the world. It is well known that the QBO is driven by vertical momentum flux from waves that propagate upward from the TTL, but it is not clear what types of waves, particularly in terms of wavelengths and frequencies, are most important for driving the QBO. Another reason the waves are of interest is that their up-and-down motions are associated with cooling and warming of the ambient air, and cooling induced by rising motions can cause water vapor to freeze into ice particles (a process called deposition). Ice formation matters because it dehydrates air as it enters the stratosphere, thereby regulating the humidity of the stratosphere, and because ice particles form cirrus clouds which affect Earth's climate by trapping outgoing infrared radiation.Work on the wave driving of the QBO focuses on waves with periods of three or four days which were found to be prominent in the previous deployments. The PIs seek to determine the three-dimensional structure of the waves and their intrinsic frequencies, factors which together determine their wave momentum flux and thus their potential importance for QBO driving. The PIs have developed techniques for probing wave structure using the fact that the RO profiles are side-looking from the balloon and measure temperature at successively lower heights with distance from the balloon gondola. The three-dimensional structure of the waves can thus be reconstructed by combining consecutive RO profiles along the balloon flight path.As for cirrus cloud formation, four of the six ROC receivers will be flown with a downward-pointing lidar called BeCOOL, the Balloon-borne Cloud Overshoot Observation Lidar (BeCOOL), developed by a French team. BeCOOL observations of cirrus clouds can be combined with ROC observations of wave-induced temperature fluctuations to determine the extent to which cirrus clouds occur in the cold phases of waves in the TTL.The work has societal value through its connections to weather forecasting. Radio occultation receivers on satellites are an important source of observations used in operational weather prediction and work performed here includes an effort to assimilate ROC observations into weather models and test their value for prediction. The data assimilation and prediction effort involves collaborations with two operational centers. In addition, weather models have difficulty simulating the QBO and its global impacts, thus better understanding of the wave driving of the QBO can contribute to better forecast models. All data from the campaign are made freely available to the global research community and can be used in a variety of ways that go beyond the goals of the campaign. The project also builds the scientific workforce by supporting two graduate students and providing internship opportunities for undergraduates including two students from the Seychelles.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.