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，东太平洋的赤道都存在强烈的降雨对比，在赤道以北的热带收敛区（ITCZ）的对流降水量很大，但南部只有云覆盖物和毛毛雨。有几个因素导致降雨的对比：在ITCZ表面，风收敛提供了振奋，低大气稳定性促进对流云，高海面温度（SSTS）通过蒸发供应水分，而相反的条件则在南部。 但是从2月左右开始，第二个ITCZ在赤道以南发展，从2月到4月，东太平洋具有双ITCZ，对流降雨北约5度北部和赤道南部。 因此上方游离对流层。 TWI的高稳定性直接抑制了ITCZ形成所需的对流，而是促进了层状（SC）云甲板，该云甲板会遮盖东南太平洋，产生冷SST，进一步劝阻对流。 冷SST还通过阻止边界层风收敛来抑制ITCZ的形成，因为边界层的风通常从较冷到更温暖的SST吹来。 该项目考虑了降低TWI在东南太平洋上的稳定性的因素，尤其是从北半球ITCZ潮湿的静态能量的运输，以及由于稳定性降低而导致Stratus Cloud覆盖率的可能降低，这可能导致SST变暖。 进一步的工作使用动量预算的分析来了解从表面风差变为融合的变化，一个想法是，跨TWI的动量运输起着重要作用。 这项工作是通过分析观察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）的大气组成模型（CESM）为项目进行的专门模拟。这项工作通过研究生的支持和培训具有更广泛的影响。 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本科生（REU）网站的NSF支持的研究经验以及大气研究大气研究与科学科学（SOARS）计划的重要机会。 由于大多数气候和地球系统模型都具有双重ITCZ偏见，因此研究结果对气候模型开发引起了人们的关注，在该偏见中，南半球ITCZ在一年中的大部分时间里都持续到太平洋的大部分时间里。该奖项反映了NSF的法定任务，并通过该基金会的知识分子优点和广泛的影响来评估NSF的法定任务。