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

为什么垂直运动剖面的底重在热带东太平洋对流 (OTREC) 组织期间发生变化

基本信息

批准号：
1759793
负责人：
Larissa Back
金额：
$ 37.37万
依托单位：
University of Wisconsin-Madison
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：
2018-03-15 至 2023-02-28
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1759793&HistoricalAwards=false
关键词：
Why Bottom Heaviness Vertical Motion

项目摘要

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.

该奖项支持热带东太平洋对流组织(OTREC)实地活动的工作。该运动力求了解赤道东太平洋和加勒比海西南部邻近但不同区域的热带对流云及其相关强降雨的形成和发展，以及它们在中美洲和哥伦比亚中间部分的演变。该运动还研究了加勒比和东太平洋每周发生的东风波的起源和演变，东风波是一种向西移动的大的大气扰动(波长约为2 000公里)。在nsf.gov/awdearch网页上，通过关键字搜索“OTREC”，就可以找到全套竞选奖项。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。考虑到东风波产生飓风的趋势，东风波对天气预报特别感兴趣。更广泛地说，热带对流是世界范围内天气和气候的引擎，但人们对此知之甚少，很难模拟。因此，在天气和气候模型中更好地表示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，该活动还包括几项教育和外联活动。其中包括支持本科生参与和制作用于课堂教学和非正规科学教育的纪录片短片。此外，PI还通过Expanding Your Horizons项目进行科学推广，该项目为大约300名中学女孩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，从而为这一研究领域的未来劳动力提供支持。八周的OTREC部署主要包括由国家大气研究中心维护的湾流V号研究飞机的一套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加勒比海西南研究地区，并使用落管探测仪和机翼安装的W波段雷达对这些地区的情况进行采样。投放探测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英尺高空)用一个小降落伞投放。雷达确定云层特性，如冰粒与液滴的相对丰度，并使用多普勒频移来测量云层中的上升气流和下降气流速度。通过在哥斯达黎加和哥伦比亚地面站点收集的观测，飞机采样得到了加强。尽管进行了密集的研究，但我们仍然缺乏一个令人满意的理论，即环境条件如何决定热带对流将在何时何地形成，持续多长时间，它将扩大和组织多少，以及它将产生多少降雨。在东太平洋，热带对流发生在赤道以北几度的东西向狭长地带，在这个地区，近地面风聚集在一个热带辐合区(ITCZ)。有令人信服的论据表明，与ITCZ中的强降雨相关的上升运动应该具有底部重垂直剖面，这意味着云中的大部分上升运动发生在对流层中下部。但是，底部重剖面的想法与卫星观测(来自NASA TRMM任务)相矛盾，卫星观测似乎显示出很大一部分层状降水。这样的降水通常是从对流广泛地区的高层云中落下的，其特征是上升运动的顶部沉重轮廓。在这个项目中，OTREC活动数据被用来解决垂直廓线的矛盾，并检验对卫星数据的另一种解释。另一个问题是ITCZ的对流在多大程度上受到该地区近地面风辐合的驱动。有些人认为(例如见AGS-1758603)，东太平洋非热带气圈的对流在很大程度上是与稳定和能量平衡有关的热力学因素造成的，近地表辐合起次要作用。在这里，PI假设热力学论点不充分，风的汇聚起主导作用。这一奖项反映了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。