Collaborative Research: The Relationship between the Trade Wind Inversion Layer and the Seasonal Development of the Southeast Pacific Inter-Tropical Convergence Zone (ITCZ)

合作研究：信风逆温层与东南太平洋热带辐合带（ITCZ）季节发展的关系

• 批准号: 2303227
• 负责人: Kadidia Thiero
• 金额: $ 3.68万
• 依托单位: University Corporation For Atmospheric Res
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-07-01 至 2026-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2303227&HistoricalAwards=false
• 关键词: Collaborative; Research; Relationship; between; Trade

For most of the year there is a strong rainfall contrast across the equator in the eastern Pacific, with heavy convective precipitation in the intertropical convergence zone (ITCZ) north of the equator but only cloud cover and drizzle to the south. Several factors contribute to the rainfall contrast: in the ITCZ surface wind convergence provides uplift, low atmospheric stability promotes convective clouds, and high sea surface temperatures (SSTs) supply moisture through evaporation, while opposite conditions hold to the south. But starting around February a second ITCZ develops south of the equator and from February to April the eastern Pacific features a double ITCZ, with convective rainfall around 5 degrees north and south of the equator. The appearance of this secondary ITCZ in the Southern Hemisphere thus provides an opportunity to understand ITCZ genesis, in particular the dynamic and thermodynamic mechanisms that produce the transition from unfavorable to favorable conditions for deep convection.Research conducted here examines the genesis of the secondary ITCZ in the southeast Pacific with a particular focus on the trade wind inversion (TWI), a shallow layer which separates the moist atmospheric boundary layer from the warmer and drier free troposphere above it. The high stability of the TWI directly inhibits the convection necessary for ITCZ formation and instead promotes the stratocumulus (Sc) cloud deck which shades the southeast Pacific, producing cold SSTs which further discourage convection. Cold SSTs also inhibit ITCZ formation by discouraging boundary layer wind convergence, as boundary layer winds generally blow from colder to warmer SST. The project considers the factors which reduce the stability of the TWI in over the southeast Pacific, looking in particular at the transport of boundary layer moist static energy from the Northern Hemisphere ITCZ, as well as the possible reduction of stratus cloud cover due to reduced stability, which could lead to warmer SSTs. Further work uses analysis of momentum budgets to understand the change from surface wind divergence to convergence, one idea being that downward momentum transport across the TWI plays an important role. The work is conducted through analysis of observational datasets and climate model simulations, as well as specialized simulations performed for the project using the Community Atmosphere Model, the atmospheric component model of the Community Earth System Model (CESM).The work has educational broader impacts through the support and training of a graduate student. In addition, the project supports undergraduate students who conduct research during the summers, in part through the NSF-supported Research Experience for Undergraduates (REU) site at Colorado State University and the Significant Opportunities in Atmospheric Research and Science (SOARS) Program run by the University Corporation for Atmospheric Research. Research results are of interest for climate model development as most climate and earth system models suffer from a double ITCZ bias, in which a Southern Hemisphere ITCZ persists for most of the year over much of the Pacific ocean.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.

一年中的大部分时间，东太平洋赤道地区的降雨量对比强烈，赤道以北的热带辐合带（ITCZ）有强对流降水，但以南只有云层和毛毛雨。造成降雨对比的因素有几个：在 ITCZ 表面风辐合产生抬升，低大气稳定性促进对流云，高海面温度 (SST) 通过蒸发提供水分，而南部则存在相反的条件。 但从 2 月左右开始，第二个 ITCZ 在赤道以南发展，从 2 月到 4 月，东太平洋出现了双 ITCZ，赤道南北各有 5 度左右的对流降雨。 因此，南半球次级 ITCZ 的出现提供了了解 ITCZ 成因的机会，特别是了解深对流从不利条件向有利条件转变的动力和热力学机制。这里进行的研究考察了南半球次级 ITCZ 的成因。东南太平洋，特别关注信风逆温层（TWI），这是一个浅层，将潮湿的大气边界层与其上方温暖干燥的自由对流层分开。 TWI 的高稳定性直接抑制了 ITCZ 形成所需的对流，反而促进了遮蔽东南太平洋的层积云 (Sc) 云层，产生冷海温，进一步阻碍对流。 冷海表温度还通过阻止边界层风辐合来抑制 ITCZ 的形成，因为边界层风通常从较冷的海表温度吹向较温暖的海表温度。 该项目考虑了降低东南太平洋上空 TWI 稳定性的因素，特别关注来自北半球 ITCZ 的边界层湿静态能量的传输，以及由于稳定性降低而可能导致的层云覆盖减少，这可能导致海表温度升高。 进一步的工作利用动量预算分析来了解从表面风发散到汇聚的变化，其中一个想法是穿过 TWI 的向下动量传输起着重要作用。 这项工作是通过对观测数据集和气候模型模拟的分析以及使用社区大气模型（社区地球系统模型（CESM）的大气成分模型）为该项目进行的专门模拟来进行的。这项工作通过以下方式具有更广泛的教育影响：研究生的支持和培训。 此外，该项目还支持在暑期进行研究的本科生，部分通过 NSF 支持的科罗拉多州立大学本科生研究体验 (REU) 网站以及由美国国家科学基金会 (NSF) 运营的大气研究和科学重大机会 (SOARS) 计划大气研究大学公司。 研究结果对气候模型开发很有意义，因为大多数气候和地球系统模型都存在双重 ITCZ 偏差，即南半球 ITCZ 在太平洋大部分地区持续存在一年中的大部分时间。该奖项反映了 NSF 的法定使命，并具有通过使用基金会的智力优点和更广泛的影响审查标准进行评估，被认为值得支持。