Dynamic and Thermodynamic Controls on Deep Convection in Organization of Tropical East Pacific Convection (OTREC)

该赠款支持热带东太平洋对流组织（OTREC）实地活动的工作。 该活动旨在了解赤道东太平洋和加勒比西南部相邻但不同区域的热带对流云和相关暴雨的形成和发展，沿着它们在中美洲和哥伦比亚中间部分的演变。 该活动还研究了东风波的成因和演变，东风波是加勒比和东太平洋每周发生的向西移动的大规模大气扰动（波长约2 000公里）。在nsf.gov/awardsearch网页上通过关键词搜索“OTREC”可获得全套活动赠款。热带对流在地球气候系统中起着关键作用，也是极端降水和飓风形成的原因。 东风波对天气预报特别感兴趣，因为它们倾向于产生飓风。 更普遍地说，热带对流是全球天气和气候的引擎，但人们对它的了解很少，也很难模拟。 因此，在天气和气候模型中更好地体现热带对流的工作，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，该运动还开展了几项教育和宣传活动。 这些措施包括支持大学生参与和制作用于课堂教学和非正式科学教育的纪录短片。 此外，主要研究者（PI）在现场活动之前，期间和之后保持博客，帮助向更广泛的受众传达科学。 该奖项还为一名研究生的教育提供资金，并为该活动带来另外三名研究生，使他们能够获得宝贵的实地工作经验。为期八周的活动部署主要包括由国家大气研究中心维护的湾流V研究飞机的20次飞行。 该活动利用哥斯达黎加的一个机场，方便进入赤道太平洋和西南加勒比研究区域，并利用下投式探空仪和机翼上的W波段雷达对这些区域的情况进行采样。 投下式探空仪包含与标准气象气球相同的仪器包，只是从飞机上（在这种情况下从大约40，000英尺）用小降落伞降落。 雷达确定云的特性，如冰粒与液滴的相对丰度，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的地面站点收集的观测资料补充了飞机取样。尽管进行了深入的研究，但我们仍然缺乏一个令人满意的理论来解释环境条件如何决定热带对流将在何时何地形成，它将持续多久，它将扩大和组织多少，以及它将产生多少降雨。 在东太平洋上，热带对流发生在赤道以北几度的东西狭长地带，该地区的近地面风聚集在热带辐合带（ITCZ）。 近地面风辐合是赤道沿着的“冷舌”和北面较暖的沃茨之间强烈的南北海表温度（SST）对比的结果。赤道附近的地面风倾向于吹过SST反差并在较暖的海面上汇聚，地面辐合引起有利于对流的上升运动，但PI反对东太平洋ITCZ的对流主要由地面辐合驱动的观点，指出地面辐合并不自动导致强对流和暴雨。 相反，他们假设，热力学因素，包括对流可用位能（CAPE），对流抑制（CIN），以及通过夹带和下沉气流的水分的影响是理解该地区对流的关键。该项目还考虑了加勒比海西南部的对流，尽管缺乏SST对比和相对干燥的大气中发生对流。 PI表明，在这些不利条件下的对流构成了一个自我维持的平衡状态，可以在给定的正确初始状态下发展，尽管相同的环境条件同样有利于抑制对流。 这种多重平衡的行为是在理想化的模式，并已与云解析模型的自聚集，和PI假设，它是牵连在活跃和抑制阶段的东风wave.The研究是使用在运动中收集的数据结合各种数值模式，包括云解析版本的天气研究和预报（WRF）模式进行。 PI有几种策略来以理想化的形式表示相关的动力学和热力学，通常使用一个小的双周期域。观察比较使用来自OTREC以及早期现场活动（EPIC和TEPPS）的数据。该奖项反映了NSF的法定使命，并被认为值得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来支持。

This grant 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 grants 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 Principal Investigators (PIs) maintain a blog during the period just before, during, and just after the field campaign, helping to communicate the science to a broader audience. The award also provides funding for the education of a graduate student and to bring three additional graduate students to the campaign, allowing them to gain valuable experience in fieldwork.The eight week campaign 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). The near-surface wind convergence is a consequence of a strong north-south sea surface temperature (SST) contrast between the "cold tongue" along the equator and the warmer waters to the north. Surface winds near the equator tend to blow across SST contrasts and converge over the warmer water, and surface convergence induces rising motions favorable to convection.But the PIs argue against the notion that convection in the eastern Pacific ITCZ is driven primarily by surface convergence, pointing out that surface convergence does not automatically result in strong convection and heavy rainfall. Instead they hypothesize that thermodynamic factors including convective available potential energy (CAPE), convective inhibition (CIN), and the influence of moisture through entrainment and downdrafts are key to understanding convection in the region.The project also considers convection over the southwest Caribbean, where convection occurs despite a lack of SST contrasts and a relatively dry atmosphere. The PIs suggest that convection in these unfavorable conditions constitutes a self-sustaining equilibrium state which can develop given the right initial state, although the same environmental conditions would equally favor suppressed convection. Such multiple equilibrium behavior is seen in idealized models and has been associated with self-aggregation in cloud resolving models, and the PIs hypothesize that it is implicated in the active and suppressed phases of easterly waves.The research is conducted using data collected during the campaign in combination with a variety of numerical models including a cloud resolving version of the Weather Research and Forecasting (WRF) model. The PIs have several strategies for representing the relevant dynamics and thermodynamics in an idealized form, often using a small doubly-periodic domain. Observational comparisons use data from OTREC as well as earlier field campaigns (EPIC and TEPPS).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.