The Dynamics and Variability of the South American Low-Level Jet (SALLJ)

南美低空急流(SALLJ)沿着安第斯山脉东坡向南流动，其最大风速在地表上方约一英里处。这股急流是南美洲气候的关键组成部分，因为它将热带大西洋的水汽带到了大陆的内陆地区。它还有助于中尺度对流系统(MCS)的形成及其产生的极端天气。在许多方面，SALLJ类似于大平原低空急流(GPLLJ)，它沿着落基山脉东侧向北流动，将水汽从墨西哥湾带到平原的粮仓。但对GPLLJ的研究至少可以追溯到20世纪50年代，而SALLJ直到20世纪80年代才被广泛记录。此外，关于小岛屿发展中国家的研究大多集中在安第斯山脉中部，从秘鲁南部到巴拉圭(东侧)，而小岛屿发展中国家联盟延伸到哥伦比亚和委内瑞拉直到2010年才有文件记载。安第斯山脉中部和北部之间的差异是显著的，因为这两个地区在气候、大范围环流机制以及与厄尔尼诺等气候模式的联系方面都不同。在这里，首席调查员(PI)对包括安第斯山脉北部和中部在内的SALLJ进行了全面的研究。PIS的初步工作表明，两个地区之间的小岛屿发展中国家在季节性上存在很大差异，安第斯山脉中部的季节性相对较弱，但北部的夏季最低值明显。这种差异促使PI假设安第斯山脉北部可能涉及不同的机制，北大西洋副热带高压的强度和位置等因素可能与此有关。另一个问题是北部分支的可变性对中心分支的影响。通过检查气象数据和使用两个气候模式(CESM2和ECHAM6)进行数值模拟来探讨这些问题。由于SALLJ变率对南美洲内陆地区的水资源和极端天气的影响，这项工作具有更广泛的影响。PIS与巴西国家自然灾害监测和预警中心的合作伙伴合作，开发监测和预报SALLJ活动和极端降水的工具。PIS还通过在其部门的地理意识周期间举办的关于气候变异性、气候变化及其社会经济影响的研讨会，开展地方外联活动。该项目支持一名博士后和一名博士后研究助理，从而为该领域的下一代研究人员提供支持和培训。该奖项反映了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。

The South American Low-level Jet (SALLJ) flows southward along the eastern slopes of the Andes, with its maximum wind speed about a mile above the surface. The jet is a key component of the climate of South America as it brings moisture from the tropical Atlantic to inland regions of the continent. It also contributes to the formation of mesoscale convective systems (MCSs) and the extreme weather they produce. In many ways the SALLJ is analogous to the Great Plains low-level jet (GPLLJ) that flows northward along the eastern side of the Rockies and brings moisture from the Gulf of Mexico to the breadbasket of the plains. But research on the GPLLJ dates back to at least the 1950s while the SALLJ was not extensively documented until the 1980s. Also, most of the research on the SALLJ is focused on the central Andes, from southern Peru to Paraguay (on the east side), and the extension of the SALLJ into Columbia and Venezuela was not documented until 2010. The distinction between the central and northern Andes is significant, as the two regions differ in their climate, large-scale circulation regimes, and connections to climate modes like El Nino.Here the Principal Investigators (PIs) conduct a comprehensive examination of the SALLJ, including both the northern and central Andes. Preliminary work by the PIs shows a strong difference in seasonality between the SALLJ between two regions, with relatively muted seasonality in the central Andes but a distinct summer minimum in the north. This difference prompts the PIs to hypothesize that different mechanisms could be involved in the northern Andes, where factors such as the strength and position of the North Atlantic Subtropical High could be relevant. A further issue is the impact of variability in the northern branch on the central branch. These issues are explored through examination of meteorological data and numerical simulations using two climate models (CESM2 and ECHAM6).The work has broader impacts due to the impact of SALLJ variability on water resources and extreme weather over inland South America. The PIs work with partners at the Brazilian National Center for Monitoring and Early Warning of Natural Disasters to develop tools for monitoring and forecasting SALLJ activity and extreme precipitation. The PIs also conduct local outreach through seminars on climate variability, climate change, and their socioeconomic impacts, presented during their department's Geography Awareness week. The project supports a PhD student and a postdoctoral research associate, thereby providing support and training to the next generation of researchers in this area.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.