Collaborative Research: Sundowner Winds EXperiment (SWEX) in Santa Barbara, California

野火是美国西部和世界其他地区最大的自然灾害之一。近年来加州发生的许多悲惨事件暴露了人们在野火面前的巨大脆弱性，以及在复杂地形下提高对风暴的了解和可预测性的迫切需要。沿海的圣巴巴拉县（SB）人口超过13万，是南加州最容易受到野火危害的社区之一。圣伊内斯山脉从沿海的SB上陡然升起，南临太平洋，北临圣伊内斯山谷。在圣伊内斯山脉的南面斜坡上经常观察到下坡、干燥和阵风的风暴。这些风通常在日落前后和整个晚上加剧，被称为“日落风”或“日落风”。它们被认为是沿海SB最重要的火灾天气制度，对航空构成危险条件。他们提高了影响SB沿海人口的所有重大野火的严重程度。因此，改善天气预警和预报提前时间，包括风力最强地区的时空特异性，对于提高对野火的抵御能力至关重要。日落现象表现出很大的时空变异性，并由独特的复杂机制驱动。日落风实验（SWEX）将研究日落风的这些独特方面，以提高对这些风的理解和可预测性，同时为在具有类似地理和气候特征的沿海环境中发展下坡风暴的新理论提供丰富的数据集。这将通过对大气过程的战略气象观测来实现，这些过程被假设为调节晚风的强度和空间变异性。这些结果将大大有助于提高沿海复杂地形下风暴的可预测性，对生活在火灾易发地区的大型社区产生重大影响。该项目将提供重要的外联材料，分发给政府机构和媒体，并将教育公众了解火灾、天气和自然灾害。此外，该项目将支持开发新的教育课程，并在美国六所大学培养本科生和研究生（包括少数民族）。日落的时空特征受到上游（圣伊内兹山谷和圣拉斐尔山脉）和下游（由于凉爽稳定的海洋边界层的影响）大气过程之间复杂相互作用的控制。SWEX活动旨在增强空间测量，以解决从边界层到对流层中层以及从SB通道到Santa Ynez山谷的局部环流和垂直剖面。这些观测结果将用于检验有关控制日落风机制的假设，评估中尺度模拟并改进日落风的提前时间预报。更具体地说，将利用多传感器平台和飞机来研究海洋和大陆边界层（BL）的结构和动力学如何在日落和无扰动期间影响山地流动，包括下坡风的强度、时间和地理特征、温度和湿度。这些测量将能够检查与高振幅山波、临界层和圣伊内斯山脉背风面风强度有关的潜在机制。这些观测结果将用于研究BL结构和对流层稳定性的变化如何控制山波流和背风坡急流，以及这些机制对日落风的可预测性的重要性。SWEX带来了尖端的科学，国家大气研究中心最先进的设施和多个仪器平台，以承担这一重要问题。它将与一个地区负责预测和火灾应对的人员建立联系，该地区具有许多具有类似脆弱性的地区的代表性。SWEX将提高美国国家气象局预测洛杉矶地区天气灾害的能力，特别是在沿海SB。因此，该项目具有广泛的影响。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

Wildfires are among the greatest natural hazards in the Western U.S. and other parts of the world. The numerous tragic events in recent years in California have exposed the great vulnerability of the population to wildfires and the critical need to improve understanding and enhance predictability of windstorms in complex terrain. Coastal Santa Barbara County (SB), with a population exceeding 130,000 inhabitants, is among the most exposed communities to wildfire hazards in southern California. The Santa Ynez Mountains rise abruptly from coastal SB separating the Pacific Ocean on its south face from the Santa Ynez Valley on its north face. Downslope, dry and gusty windstorms are frequently observed on the southern-facing slopes of the Santa Ynez Mountains. These winds typically intensify around sunset and throughout the night, and are known as "Sundowner winds" or "Sundowners". They are considered the most significant fire-weather regime in coastal SB and pose hazardous conditions to aviation. They have enhanced the severity of all major wildfires affecting the SB coastal population. Therefore, improved weather warnings and forecast lead time, including spatiotemporal specificity of where winds will be strongest, are critical to increase resilience to wildfires. Sundowners exhibit large spatiotemporal variability and are driven by unique complex mechanisms. The Sundowner Winds Experiment (SWEX) will investigate these unique aspects of Sundowners to advance the understanding and predictability of these winds, while providing rich data sets for developing new theories of downslope windstorms in coastal environments with similar geographic and climatic characteristics. This will be accomplished with strategic meteorological observations of the atmospheric processes hypothesized to modulate Sundowner winds intensity and spatial variability. These results will significantly contribute to improve the predictability of windstorms in complex terrain in coastal environments, with significant impacts to large communities living in fire prone areas. The project will provide key outreach materials for dissemination to government agencies and the media and will educate the public about fire weather and natural disasters. Moreover, the project will support the development of new educational courses, and the training of undergraduate and graduate students, including minorities, in six universities in the U.S. Sundowners spatiotemporal characteristics are controlled by complex interactions between atmospheric processes occurring upstream, in the Santa Ynez Valley and San Rafael Mountains, and downstream due to the influence of a cool and stable marine boundary layer. The SWEX campaign is designed to enhance spatial measurements to resolve local circulations and vertical profiles from the boundary layer to the mid-troposphere, and from the SB channel to the Santa Ynez Valley. These observations will be used to test hypotheses concerning the mechanisms controlling Sundowner winds, evaluate mesoscale simulations and improve lead time forecasts of Sundowners. More specifically, the multi-sensor platforms and aircraft will be utilized to investigate how the structure and dynamics of the marine and continental Boundary Layers (BL) influence mountain flows during Sundowners and undisturbed periods, including intensity, timing and geographic characteristics of downslope winds, temperatures and humidity. These measurements will enable to examine underlying mechanisms relating high amplitude mountain waves, critical layers, and surface wind intensity leeward of the Santa Ynez Mountains. These observations will be utilized to investigate how variations in BL structure and tropospheric stability control mountain wave flows and the lee-slope jet, and the importance of these mechanisms for the predictability of Sundowner winds. SWEX brings cutting-edge science, the state-of-art facilities at National Center for Atmospheric Research and multiple instrumental platforms to bear on this important problem. It will build linkages with those responsible for predictions and fire response in a region that is representative of many areas with similar vulnerabilities. SWEX will improve the capability of the National Weather Service to forecast weather hazards in the Los Angeles area, specifically in coastal SB. Thus this project has substantial broader impacts.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.