The Precipitation Response to El Niño/Southern Oscillation (ENSO) over Tropical South America: Spatial and Temporal Heterogeneity and the Role of the Land Surface

南美洲热带地区降水对厄尔尼诺/南方涛动（ENSO）的响应：时空异质性以及地表的作用

• 批准号: 1505198
• 负责人: Benjamin Lintner
• 金额: $ 45.96万
• 依托单位: Rutgers University New Brunswick
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-08-01 至 2019-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1505198&HistoricalAwards=false
• 关键词: Precipitation; Response; El; Ni; Southern

El Nino/Southern Oscillation (ENSO) events are known to have significant impacts on weather and climate worldwide, including reductions in rainfall over much of tropical South America with associated disruptions to water resources, agriculture, and other human and natural systems. The rainfall anomalies are ultimately due to changes in the large-scale atmospheric circulation induced by ENSO conditions in the neighboring equatorial Pacific, but they may also be modulated by land-atmosphere coupling occurring over South America. Here land-atmosphere coupling refers to several mechanisms through which the condition of the land surface influences precipitation, one of which is that soil moisture serves as a source of water vapor through evaporation and transpiration, thereby promoting precipitation. This sort of "precipitation recycling" can prolong and enhance dry spells, as lack of rain dries the soil and reduces evapotranspiration, leading to further reductions in rainfall. On the other hand, a drier land surface can mean greater heating of the land surface during the day as there is less evaporative cooling, and a hotter land surface can lead to instability in the atmospheric boundary layer, which increases the chances of convective precipitation. Land-atmosphere coupling can be quite variable depending on land cover and other factors, and can thus cause the rainfall response to ENSO events to be more spatially variable that would be expected from the large-scale atmospheric circulation anomalies. It can also cause changes in the frequency, intensity, and duration of daily and sub-daily rainfall episodes within the period of a season or more during which an ENSO event takes place.The goal of this project is to determine the extent to which land-atmosphere coupling accounts for the spatial heterogeneity in the rainfall response to ENSO events over tropical South America. The research consists in large part of statistical analysis of precipitation and atmospheric and land surface data for tropical South America, taken from satellite and surface observations and reanalysis products. Parallel analysis is applied to model simulations from the Coupled Model Intercomparison Project version 5 (CMIP5), including simulations from the subset of models which contributed to the CMIP5 Global Land-Atmosphere Coupling Experiment (GLACE-CMIP5), in which models were integrated using climatological soil moisture so that land-atmosphere coupling could be assessed by comparison between simulations with interactive and fixed soil moisture. The statistical assessment is accompanied by model experiments using the quasi-equilibrium tropical circulation model version 2 (QTCM2), a simplified model which can simulate key aspects of the precipitation response over tropical South America, and in which key factors such as soil moisture, surface sensible heat flux, and the exchange of heat and water vapor between the boundary layer and the overlying free troposphere can be controlled and examined.Work under this project has important broader impacts in addition to its scientific merit, given the substantial consequences of ENSO-related precipitation disruptions in the region. The results of this study are also expected to shed light on the role of land-atmosphere coupling in other regions of the tropics where similar surface conditions prevail. The work also promotes international collaboration, as it involves unfunded collaborators in two Columbian universities. Aside from the broader impacts of the research, the project also supports undergraduate research assistants through the Research in Science and Engineering (RiSE) program, a 10-week summer program which focuses on students from traditionally underrepresented populations. In addition, the project provides support and training to a graduate student, thereby providing for the next generation of the scientific workforce in this research area.

众所周知，厄尔尼诺/南方涛动（ENSO）事件对全球天气和气候产生重大影响，包括南美洲热带大部分地区降雨量减少，并对水资源、农业和其他人类和自然系统造成相关干扰。 降水异常最终是由于ENSO条件在邻近的赤道太平洋引起的大尺度大气环流的变化，但它们也可能是调制发生在南美洲的陆-气耦合。 这里的陆气耦合是指陆面条件影响降水的几种机制，其中之一是土壤水分通过蒸发和蒸腾作为水汽来源，从而促进降水。 这种“降水再循环”可以延长和加强干旱期，因为缺乏雨水会使土壤干燥，减少蒸散，导致降雨量进一步减少。 另一方面，干燥的陆地表面可能意味着白天陆地表面的加热更大，因为蒸发冷却较少，而较热的陆地表面可能导致大气边界层的不稳定，这增加了对流降水的机会。 根据土地覆盖和其他因素的不同，陆地-大气耦合可能变化很大，因此可能导致降雨对厄尔尼诺/南方涛动事件的反应在空间上变化更大，这是从大尺度大气环流异常中预期的。 它也可以导致的频率，强度和持续时间的变化，每日和亚每日降雨事件的一个赛季或更长的时间内，在ENSO事件happened.The项目的目标是确定在何种程度上，陆地-大气耦合占热带南美洲的降雨响应ENSO事件的空间异质性。 这项研究的大部分内容是对来自卫星和地面观测以及再分析产品的南美洲热带地区的降水、大气和陆地表面数据进行统计分析。 并行分析应用于耦合模式相互比较项目第5版（CMIP 5）的模式模拟，包括CMIP 5全球陆地-大气耦合实验（GLACE-CMIP 5）的模型子集的模拟，在该实验中，使用气候学土壤水分将模型集成，以便通过相互作用和固定土壤水分模拟之间的比较来评估陆地-大气耦合。 统计评估伴随着使用准平衡热带环流模式第二版（QTCM 2）的模式实验，该模式是一个简化模式，可以模拟热带南美洲降水响应的关键方面，其中包括土壤湿度，地表感热通量，边界层和上覆的自由对流层之间的热量和水汽交换可以被控制和检查。此外，本项目下的工作具有重要的更广泛的影响考虑到厄尔尼诺/南方涛动对该区域降水造成的严重影响， 这项研究的结果也有望揭示陆地-大气耦合在热带其他地区的作用，类似的表面条件占主导地位。 这项工作还促进了国际合作，因为它涉及哥伦比亚两所大学的无资金合作者。 除了研究的更广泛影响外，该项目还通过科学与工程研究（RiSE）计划支持本科生研究助理，这是一个为期10周的暑期项目，重点关注传统上代表性不足的学生。 此外，该项目还为一名研究生提供支持和培训，从而为这一研究领域的下一代科学工作者提供支持。