OTREC: Convective Heating Profiles and the Transition from Shallow to Deep Convection over the Tropical East Pacific and Southwest Caribbean

OTREC：热带东太平洋和西南加勒比地区的对流加热剖面以及从浅对流到深对流的转变

• 批准号: 1759255
• 负责人: Zhiming Kuang
• 金额: $ 38.22万
• 依托单位: Harvard University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-07-01 至 2023-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1759255&HistoricalAwards=false
• 关键词: OTREC; Convective; Heating; Profiles; Transition

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 includes several education and outreach activities including support for undergraduates to participate in fieldwork and production of short documentary videos for use in classroom teaching and informal science education. Work performed under this award fosters international scientific collaboration with scientists in Colombia and Costa Rica and helps to develop local infrastructure for rainwater collection and isotopic analysis.The eight week OTREC deployment consists primarily of a set of 20 flights in the Gulfstream V (GV) research aircraft maintained by the National Center for Atmospheric Research (NCAR). 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. Work performed here augments the aircraft observations through the collection and analysis of rainwater samples from ground sites in Costa Rica and Colombia.Despite intensive study we 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. Vertical structure is a key property of tropical convection that determines its evolution and its interactions with the circulation and thermodynamics of the surrounding atmosphere. The vertical structure can be simply characterized as top- or bottom-heavy, according to the relative amounts of rising motion that occur in the upper and lower troposphere.Work conducted here seeks to determine the vertical structure of tropical convection by measuring the ratios of stable isotopes in rainwater produced by it. Rainwater is almost entirely composed of ordinary H2O, but it contains trace amounts of water in which deuterium (D) replaces hydrogen (H) to form HDO, or oxygen-18 replaces oxygen-16. These heavier isotopes condense more readily than ordinary H2O and are thus more common in raindrops formed lower rather than higher in the troposphere. The relative abundance of heavier isotopes in raindrops should thus provide a means to determine if they formed in top-heavy or bottom-heavy convection. Rainwater collection for isotopic analysis is planned at three sites in Colombia: Nuqui, on the west coast; Quibdo, further inland; and Isla San Andres, in the southwest Caribbean. Estimates of convective vertical profiles from isotopic composition are compared with estimates from aircraft measurements to determine if the method works. Further examination of the isotopic data would be conducted using numerical simulations from a variety of atmospheric models including some in which tracer "particles" representing water vapor are tracked as they rise through cloud systems and ultimately condense.A further goal of the research is to understand the transition from shallow to deep convection, a critical component of the lifecycle of convective clouds. Three contributing factors in the transition are examined: the gradual moistening of the atmospheric boundary layer; organization of the subcloud layer, which allows cloud roots to form in air which has greater moisture than the large-scale mean; and cold pools formed by convective downdrafts, which organize the subcloud layer to produce larger cloud roots which are in turn less susceptible to the diluting effect of dry air entrainment. The third of these factors may lead to a positive feedback, in which convective downdrafts organize the subcloud layer in a way that further promotes convection. Better characterization of entrainment is of particular interest over the southwest Caribbean, as midtropospheric air in this region is quite dry yet convection still occurs.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.

该奖项支持在热带东太平洋对流组织（OTREC）现场运动中的工作。该运动旨在了解热带对流云的形成和发展，以及在赤道太平洋和西南加勒比海的相邻但不同地区的大雨，以及中美洲和哥伦比亚的中间地区的演变。该运动还研究了东方波浪的起源和演变，大气向西的大气干扰（大约2,000公里的波长）每周在加勒比海和东太平洋中每周发生。通过在“ OTREC”上的关键字搜索的NSF.GOV/AWARDERCHEARCEREARG网页上可以发现全套竞选奖项。热带对流在地球的气候系统中起着至关重要的作用，并且也负责极端的降水和飓风形成。鉴于天气预报的趋势趋于产卵，因此对天气预报特别感兴趣。更一般而言，热带对流是全球天气和气候的引擎，但理解且难以模拟。因此，在天气和气候模型中更好地代表热带对流的工作可以为公众和决策者带来更好的天气预测和影响评估。除了科学的社会相关性外，该运动还包括几项教育和推广活动，包括支持本科生参与现场工作和制作简短的纪录片视频，以用于课堂教学和非正式科学教育。 根据该奖项进行的工作促进了与哥伦比亚和哥斯达黎加的科学家的国际科学合作，并有助于开发当地的基础设施，以进行雨水收集和同位素分析。八周OTREC部署主要由墨西哥湾V（GV）V（GV）研究中的20套航班组成。 该活动使用哥斯达黎加的机场轻松进入赤道太平洋和西南加勒比海研究区，这些地区的条件是使用Dropsondes和机翼安装的W波段雷达进行采样的。 Dropsondes包含与标准气球相同的仪器包装，仅从飞机（在这种情况下从约40,000英尺）掉落，带有小型降落伞。 这里进行的工作通过收集和分析哥斯达黎加和哥伦比亚地面地点的雨水样品来增强飞机的观察。尽管进行了密集研究，但我们缺乏令人满意的理论，即环境条件如何确定热带对流的何时形成，何时形成，它将持续多长时间，它将持续多长时间，它将扩展和组织多少雨水，以及它会产生多少雨水。垂直结构是热带对流的关键特性，它决定了其演变及其与周围气氛的循环和热力学的相互作用。 垂直结构可以简单地将其表征为顶部或底部的重量，根据对流层上和下部的相对上升运动的相对量。此处进行的工作试图通过测量其产生的雨水中稳定同位素的比率来确定热带对流的垂直结构。 雨水几乎完全由普通的H2O组成，但其中含有痕量的水，其中氘（d）代替氢（H）形成HDO，或者氧-18代替了氧气16。 这些较重的同位素比普通的H2O更容易凝结，因此在雨滴中更为常见，而在对流层中比更高的雨滴中更为常见。 因此，雨滴中较重的同位素的相对丰度应提供一种方法，以确定它们是在高度或底部重的对流中形成的。计划在哥伦比亚的三个地点进行同位素分析的雨水收集：西海岸的Nuqui； Quibdo，更内陆；和西南加勒比海的伊斯拉·圣安德烈斯（Isla San Andres）。将同位素组合物中对流垂直轮廓的估计值与飞机测量的估计值进行了比较，以确定该方法是否有效。 将使用来自各种大气模型的数值模拟进行进一步检查，包括一些大气模型，其中一些代表水蒸气的示踪剂“颗粒”在通过云系统上升并最终凝结时跟踪它们。研究的进一步目标是了解从浅层对流到深层对流的过渡，这是对交流云的生命周期的关键组成部分的重要组成部分。 检查了过渡中的三个促成因素：大气边界层的逐渐湿润；子云层的组织，该层允许在空气中形成云根，该空气具有比大规模平均值更大的水分。以及由对流下降气流形成的冷水池，它们组织了子云层，以产生较大的云根，而云根又不容易受到干燥空气夹带的稀释作用的影响。这些因素中的三分之一可能导致积极的反馈，其中对流下水道以进一步促进对流的方式组织了子云层。 在加勒比西南部，更好地表征夹带是特别感兴趣的，因为该地区的中间环空气中的中间层空气非常干燥，但仍会发生对流。该奖项反映了NSF的法定任务，并且被认为值得通过基金会的知识分子优点和更广泛的影响标准通过评估来进行评估。