Collaborative Research: Understanding the Influence of Turbulent Processes on the Spatiotemporal Variability of Downslope Winds in Coastal Environments

沿海地区的下坡风暴导致了许多严重的野火。导致这些风暴的总体条件是众所周知的，然而，由于缺乏对复杂地形中驱动最猛烈风的小规模机制的了解，有关风的时间和严重程度的细节很难预测。该奖项为加利福尼亚圣巴巴拉沿海地区日落风实验数据的分析和数值模拟提供资金。日落风是圣巴巴拉地区的一种特殊类型的下坡风暴，它的名字来自于风在晚上和夜间加强的趋势。研究小组计划采用多方面的方法从这个项目中提供社会效益，包括与当地国家气象局办公室和圣巴巴拉县消防局合作。学生将参与该项目，并将在加利福尼亚州和弗吉尼亚州的K-12和社区学院进行推广。本项目的总体目标是通过观测和数值模拟相结合，进一步了解下坡风暴与沿海山区上下游大气边界层特征之间的相互作用。日落风实验（SWEX）于2022年4月1日至5月15日在加利福尼亚州圣巴巴拉附近的沿海地形进行。日落风是圣伊内斯山脉南坡上的一种干燥且阵风的下坡风，可能与关键的火灾天气条件有关。该项目将使用SWEX数据集，并使用天气研究与预报模型（WRF-km， 1.25km网格间距）和大涡模拟（LES， 50m网格间距）进行数值模拟，以提高对背风坡喷流和近地面风变率相关机制的理解。研究小组还将调查WRF-km模拟中的偏差。研究的主要目标有三个：1)利用SWEX观测资料确定日落和静息期背风坡风结构时空变化的机制。2)检验WRF-km表征背风坡风结构的能力，识别导致模式偏差的相关过程。3)研究了50m栅格距处的LES在表征背风坡风结构方面的性能，以及湍流过程对模拟地面风偏置的贡献。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。

Downslope windstorms in coastal terrain have resulted in many serious wildland fires. The overall conditions leading to those windstorms are well-known, however the details about the timing and severity of the winds are difficult to forecast due to a lack of knowledge about the small-scale mechanisms that drive the most severe winds in complex terrain. This award provides funding for the analysis and numerical modeling of data from the Sundowner Wind Experiment in the coastal Santa Barbara region of California. Sundowner winds are a specific type of downslope windstorm in the Santa Barbara area and they get their name from the tendency of the winds to strengthen into the evening and overnight hours. The research team plans a multi-faceted approach to provide societal benefits from this project, including working with the local National Weather Service office and Santa Barbara County Fire Department. Students will be involved with the project and outreach will be conducted at K-12 and community colleges in California and Virginia.The overarching goal of this project is to advance the understanding of interactions between downslope windstorms and upstream/downstream atmospheric boundary layer characteristics in coastal mountains by combining observations and numerical simulations. The Sundowner Winds Experiment (SWEX) was conducted from April 1 to May 15, 2022, in the coastal topography surrounding Santa Barbara, CA. Sundowner winds are a dry and gusty downslope wind on the southern facing slope of the Santa Ynez Mountains that can be associated with critical fire weather conditions. This project will use SWEX datasets and perform numerical simulations using the Weather Research and Forecasting model (WRF-km, 1.25km grid spacing) and Large Eddy Simulations (LES, 50m grid spacing) to improve the understanding of mechanisms associated with lee slope jets and near-surface wind variability. The research team will also investigate biases in WRF-km simulations. Three main objectives are targeted:1) Identify mechanisms responsible for the spatiotemporal variability of lee slope wind structure during Sundowners and quiescent periods using SWEX observations.2) Examine the skill of WRF-km in representing lee slope wind structure and identify relevant processes contributing to model biases.3) Investigate the performance of LES at 50m grid spacing in representing lee slope wind structure, and the contribution of turbulent processes to biases in simulated surface winds.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.