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: 2303225
• 负责人: Alex Gonzalez
• 金额: $ 65.05万
• 依托单位: Woods Hole Oceanographic Institution
• 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=2303225&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.

在一年中的大部分时间里，东太平洋赤道地区的降水对比很强，赤道以北的热带辐合带（ITCZ）有强对流降水，但南部只有云层和毛毛雨。有几个因素促成了降雨量的对比：在ITCZ表面，风的辐合提供了隆起，低大气稳定性促进了对流云，高海面温度（SST）通过蒸发提供水分，而相反的情况在南部。 但从2月开始，赤道以南会形成第二个ITCZ，从2月到4月，东太平洋会形成两个ITCZ，赤道以北和以南5度左右会有对流降雨。 因此，南半球次级ITCZ的出现提供了一个了解ITCZ成因的机会，特别是动力学和热力学机制，产生从不利到有利的深对流条件的转变。这里进行的研究探讨了东南太平洋次级ITCZ的成因，特别是贸易风逆温（TWI），将潮湿的大气边界层与其上较温暖和干燥的自由对流层分隔开的一个浅层。TWI的高稳定性直接抑制了ITCZ形成所需的对流，反而促进了层积云（Sc）的形成，使东南太平洋蒙上阴影，产生冷的SST，进一步阻碍了对流。 由于边界层风通常从较冷的SST吹向较暖的SST，因此较冷的SST也会阻碍边界层风的辐合，从而抑制ITCZ的形成。 该项目考虑了降低东南太平洋TWI稳定性的因素，特别关注来自北方ITCZ的边界层湿静能的输送，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SST变暖。 进一步的工作使用动量收支分析来理解从地面风辐散到辐合的变化，其中一个想法是TWI的向下动量输送起着重要作用。 通过分析观测数据集和气候模型模拟，以及使用社区大气模型（社区地球系统模型（CESM）的大气组成模型）为项目进行的专门模拟，开展了这项工作。通过支持和培训一名研究生，这项工作产生了更广泛的教育影响。 此外，该项目还支持在夏季进行研究的本科生，部分是通过科罗拉多州立大学的NSF支持的本科生研究经验（REU）网站和由大学大气研究公司运行的大气研究和科学（SOARS）计划的重要机会。 研究结果对气候模式的发展很有意义，因为大多数气候和地球系统模式都存在双重ITCZ偏差，即南半球的ITCZ在一年的大部分时间里持续存在于太平洋的大部分地区。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。