The Organization of Tropical East Pacific Convection (OTREC) Field Campaign: Support for Field Activities and Post-Campaign Analysis

这笔赠款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网页上搜索“OTREC”，即可找到整套活动赠款。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。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。除了科学的社会意义外，这项运动还包括几项教育和外联活动，包括支持本科生参加实地考察和制作用于课堂教学和非正式科学教育的纪录片短片。此外，这笔赠款的首席调查人员(PI)将这项活动的结果纳入到他们对新墨西哥高中的宣传中，部分是通过新墨西哥理工大学科学硕士教学计划中提供的关于天气和气候的课程。他们还为他们所在的州的K-12课堂教学开发材料。该项目支持一名研究生和一名博士后研究员，从而为这一研究领域的未来劳动力提供支持。为期八周的OTREC部署主要包括由国家大气研究中心(NCAR)维护的一套20架湾流V(GV)研究飞机。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4万英尺高空)用一个小降落伞投放。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将在何时何地形成、持续多长时间、它将膨胀和组织多少以及它将产生多少降雨，我们缺乏一个令人满意的理论。PIS发展了一种理论，认为温暖海洋上的深度对流由三个热力学因素控制：来自底层海洋的热量和水分、大气柱的“饱和分数”(一种整体相对湿度)和潮湿对流不稳定(较弱的不稳定与较大的降雨之间存在违反直觉的联系)。但该理论假设大气和海洋条件一致，而这一假设在赤道东太平洋可能不成立。相反，该地区的特点是海表面温度(SST)存在巨大的南北对比，并伴随着一条狭窄的东西向对流带，称为热带辐合带(ITCZ)。强烈的海温对比度为ITCZ对流提供了另一种解释，因为近地表的风通常会吹过温差，并在较暖的海温上汇合。低层风汇聚的上升运动可以产生对流，但根据SST对比论证，观测到的对流并不明显符合预期。另一个问题涉及对流云的垂直结构，因为东太平洋ITCZ的对流云相对较浅，但它们产生的降雨率与西太平洋较深的对流云相似。PIs对中深层对流暴雨的发展有一个解释，这可以用活动数据进行测试。另一个谜团是，来自NASA热带降雨测量任务(TRMM)的卫星数据似乎显示，东太平洋有大量层状降雨，尽管高层状降雨比例通常与在深对流地区发现的砧状云和腐烂的云羽有关。PIS认为，在TRMM数据中被识别为层状雨的云特征应该被归类为弱蜂窝对流，从而消除层状雨量和相对浅对流之间的不一致。滴落探空仪和机载雷达资料的结合应该足以区分层状雨云和弱细胞对流。相比之下，加勒比海西南部的海温相当均匀，因此对流不是由海温引起的风辐合发展而来的。此外，该地区对流层中层空气相对干燥，不利于对流和暴雨。然而，对流和暴雨仍在发生，通常与东风波的通过有关。这些海浪每周出现一次，有时会穿过中美洲到达东太平洋。但尚不清楚东太平洋的大部分东风波是来自加勒比海，还是在当地形成。这些问题也在活动中得到了解决。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。

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 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. In addition, the Principal Investigators (PIs) of this grant incorporate results from the campaign into their outreach to New Mexico high schools, in part through a class on weather and climate offered in the Masters of Science Teaching program at New Mexico Tech. They also develop materials for K-12 classroom teaching in their state. The project supports a graduate student and a postdoctoral research fellow, thereby providing for the future workforce in this research area.The eight-week OTREC deployment consists primarily of a set of 20 flights of 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.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. The PIs have developed a theory in which deep convection over warm oceans is controlled by three thermodynamic factors: heat and moisture coming from the underlying ocean, the "saturation fraction" of the atmospheric column (a kind of bulk relative humidity), and moist convective instability (with a counterintuitive association between weaker instability and heavier rainfall). But the theory assumes uniform atmospheric and oceanic conditions, and this assumption may not hold in the eastern equatorial Pacific. Instead, the region features a large north-south contrast in sea surface temperature (SST) accompanied by a narrow east-west convection band called the intertropical convergence zone (ITCZ). The sharp SST contrast provides an alternative explanation for ITCZ convection, as near-surface winds generally blow across the temperature contrast and converge over the warmer SSTs. Rising motion where low-level winds converge can produce convection, but the observed convection does not clearly match expectations based on SST contrast arguments.A further issue involves the vertical structure of convective clouds, as convective clouds in the eastern Pacific ITCZ are relatively shallow yet they produce rain rates similar to their deeper counterparts over the western Pacific. The PIs have an explanation for the development of heavy rain from mid-depth convection which can be tested using campaign data. A further mystery is that satellite data from the NASA Tropical Rainfall Measurement Mission (TRMM) seem to show a large amount of stratiform rain in the eastern Pacific, even though high stratiform rain fraction is usually associated with the anvil cloud and decaying cloud plumes found in regions of deep convection. The PIs argue that cloud features identified as stratiform rain in TRMM data should instead be classified as weak cellular convection, thus removing the inconsistency between stratiform rain amounts and relatively shallow convection. The combination of dropsonde and airborne radar data should suffice to distinguish between stratiform rain clouds and weak cellular convection.In contrast, SSTs in the southwest Caribbean are quite uniform so convection does not develop from SST-induced wind convergence. Moreover, mid-tropospheric air over the area is relatively dry and thus not conducive to convection and heavy rainfall. Yet convection and heavy rainfall still occur, often associated with the passage of easterly waves. These waves appear on a weekly basis and sometimes cross Central America to reach the eastern Pacific. But it is not clear whether the majority of easterly waves in the eastern Pacific come from the Caribbean or if they form locally. These issues are also addressed in the campaign.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.