Why Bottom-Heaviness of Vertical Motion Profiles Varies during Organization of Tropical East Pacific Convection (OTREC)

该奖项支持热带东太平洋对流组织（OTREC）实地活动的工作。该运动旨在了解赤道东太平洋和加勒比海西南部邻近但不同的地区热带对流云的形成和发展及其相关的强降雨，以及它们在中美洲和哥伦比亚中间部分的演变。该运动还检查了每周在加勒比和东太平洋发生的东风波的起源和演变，即向西移动的大型大气扰动（波长约2000公里）。通过“OTREC”关键字搜索，可以在nsf.gov/awardsearch网页上发现全套活动奖项。热带对流在地球气候系统中起着至关重要的作用，也是极端降水和飓风形成的原因。由于东风浪有产生飓风的倾向，因此对天气预报特别感兴趣。更一般地说，热带对流是全球天气和气候的引擎，但人们对它知之甚少，也难以模拟。因此，在天气和气候模式中更好地表现热带对流的工作可以为公众和决策者带来更好的天气预报和影响评估。除了科学的社会相关性外，该运动还包括一些教育和外展活动。这些措施包括支持本科生参与和制作用于课堂教学和非正式科学教育的短纪录片。此外，PI还通过“拓展你的视野”项目开展科学推广，该项目为大约300名中学女生举办了为期一天的会议，让她们有机会探索使用数学和科学的职业。该项目还为两名研究生提供支持和培训，从而为该研究领域的未来劳动力提供支持。为期八周的OTREC部署主要包括在国家大气研究中心维护的湾流V研究飞机上进行20次飞行。该活动使用哥斯达黎加的一个机场，方便进入赤道太平洋和加勒比海西南部的研究区域，并使用下投探空仪和安装在机翼上的w波段雷达对这些区域的情况进行采样。下落探空仪包含与标准气象气球相同的仪器包，只是用一个小降落伞从飞机上（在这种情况下，从大约4万英尺的高度）扔下。雷达确定云的特性，如冰粒和液滴的相对丰度，并使用多普勒频移测量云中的上升气流和下降气流速度。在哥斯达黎加和哥伦比亚地面站点收集的观测资料加强了飞机取样。尽管进行了深入的研究，但对于环境条件如何决定热带对流何时何地形成、持续多长时间、扩大和组织多少以及产生多少降雨，我们仍然缺乏一个令人满意的理论。在东太平洋上空，热带对流发生在赤道以北几度的一条狭窄的东西狭长地带，在这里，近地面的风聚集在一个热带辐合带（ITCZ）。有令人信服的论点认为，与ITCZ强降雨相关的上升运动应该有一个底部重的垂直剖面，这意味着云层中的大部分上升运动发生在对流层的中下层。但是，卫星观测（来自美国宇航局TRMM任务）似乎显示了很大一部分层状降水，这与底部重剖面的观点相矛盾。这种降水通常来自广泛对流区域的高层云层，其特征是上升运动的头重剖面。在本项目中，OTREC战役数据用于解决垂直剖面矛盾，并测试卫星数据的替代解释。进一步的问题是该区域近地面风辐合在多大程度上驱动了ITCZ内的对流。一些人认为（例如参见AGS-1758603）东太平洋ITCZ的对流主要是由于与稳定性和能量平衡相关的热力学因素，近地面辐合起次要作用。在这里，PI假设热力学论据不充分，风辐合起主导作用。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 work on the Organization of Tropical East Pacific Convection (OTREC) field campaign. The campaign seeks to understand the formation and development of tropical convective clouds and associated heavy rainfall in the adjacent but distinct regions of the eastern equatorial Pacific and the southwest Caribbean, along with their evolution over the intervening portions of Central America and Colombia. The campaign also examines the genesis and evolution of easterly waves, large westward-moving atmospheric disturbances (wavelengths of about 2,000 km) which occur on a weekly basis in the Caribbean and eastern Pacific. The full set of campaign awards is discoverable on the nsf.gov/awardsearch webpage by a keyword search on "OTREC".Tropical convection plays a critical role in earth's climate system and is also responsible for extreme precipitation and hurricane formation. Easterly waves are of particular interest for weather forecasting given their tendency to spawn hurricanes. More generally, tropical convection is an engine of weather and climate worldwide yet poorly understood and difficult to simulate. Work leading to better representation of tropical convection in weather and climate models can thus lead to better weather forecasts and impact assessments, both for the public and decision makers. Aside from the societal relevance of the science, the campaign features several education and outreach activities. These including support for undergraduate participation and production of short documentary videos for use in classroom teaching and informal science education. In addition, the PI performs science outreach through the Expanding Your Horizons program, which conducts a one-day conference for about 300 middle school girls, giving them the opportunity to explore careers that use math and science. The project also provides support and training for two graduate students, thereby providing for the future workforce in this research area.The eight week OTREC deployment consists primarily of a set of 20 flights in the Gulfstream V research aircraft maintained by the National Center for Atmospheric Research. The campaign uses an airport in Costa Rica for easy access to the equatorial Pacific and southwest Caribbean study regions, and conditions in these regions are sampled using dropsondes and a wing-mounted W-band radar. Dropsondes contain the same instrument package as standard weather balloons, only dropped from an aircraft (in this case from about 40,000 feet) with a small parachute. The radar determines cloud properties such as the relative abundance of ice particles versus liquid droplets, and uses Doppler shift to measure updraft and downdraft speeds in clouds. The aircraft sampling is augmented by observations collected at ground sites in Costa Rica and Colombia.Despite intensive study we still lack a satisfactory theory for how environmental conditions determine when and where tropical convection will form, how long it will last, how much it will expand and organize, and how much rain it will produce. Over the eastern Pacific tropical convection occurs in a narrow east-west strip a few degrees north of the equator, in a region where near-surface winds come together in an intertropical convergence zone (ITCZ). There are convincing arguments that rising motions associated with heavy rainfall in the ITCZ should have a bottom-heavy vertical profile, meaning that the bulk of the rising motion in clouds occurs in the lower and middle troposphere. But the idea of a bottom-heavy profile is contradicted by satellite observations (from the NASA TRMM mission) which appear to show a large fraction of stratiform precipitation. Such precipitation typically falls from upper-level clouds in regions of widespread convection characterized by a top-heavy profile of rising motion. In this project OTREC campaign data is used to resolve the vertical profile contradiction and test an alternative interpretation of the satellite data.A further issue is the extent to which convection in the ITCZ is driven by the near-surface wind convergence in the region. Some argue (see for example AGS-1758603) that convection in the eastern Pacific ITCZ is largely due to thermodynamic factors associated with stability and energy balance, with near-surface convergence playing a secondary role. Here the PI hypothesizes that the thermodynamic arguments are not sufficient and the wind convergence plays a dominant role.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.