Abstract Sundowner winds are a type of downslope windstorms observed on the southern slopes of the Santa Ynez Mountains (SYM) in Santa Barbara, southern California. The name “Sundowner” is due to the onset of strong winds near sunset. Sundowner winds can reach gale force and are extremely dangerous during wildfires. This study presents a climatology of Sundowners based on a 30 yr high spatiotemporal resolution dataset obtained with the Weather Research and Forecasting model. Combined empirical orthogonal function (EOF) analysis of hourly zonal and meridional winds (10 m) with 1 km grid spacing is performed to characterize the diurnal variability of surface winds. The first two eigenmodes (EOF-1, EOF-2) (58% of total variance) characterize the variability of surface winds in the western and eastern parts of the SYM, respectively. The hourly percentiles of the frequency distribution of the first two time coefficients (PC1, PC2) are used to identify three types of Sundowner regimes. The western (eastern) regime occurs when surface winds project strongly on EOF-1 (EOF-2) but not on EOF-2 (EOF-1). The western regime is characterized by a strong coastal jet around Point Conception with northwesterly winds extending into the Santa Barbara Channel. In contrast, a weak coastal jet not extending into the Santa Barbara Channel is observed in the eastern regime. In the Santa Barbara (SBA) regime, hourly surface winds project strongly on both EOF-1 and EOF-2. The western regime occurs more frequently than the eastern and SBA regimes and peaks during March-May. The eastern regime has maximum in January-February, whereas the SBA regime has a seasonal cycle similar to the western regime. Horizontal and vertical structures of winds and potential temperature show that the lee slope jet and mountain wave activity on the SYM exhibit strong spatial variations in the three regimes.

中文翻译：

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加利福尼亚州圣巴巴拉沿海日落风的气候学，基于 30 年高分辨率 WRF 降尺度

摘要 日落风是在加利福尼亚州南部圣巴巴拉的圣伊内斯山脉 (SYM) 南坡观察到的一种下坡风暴。“日落者”这个名字是因为日落时分会刮起强风。日落时风可以达到烈风，在野火期间极其危险。本研究基于使用天气研究和预测模型获得的 30 年高时空分辨率数据集，展示了日落者的气候学。对网格间距为 1 km 的每小时纬向和经向风 (10 m) 进行组合经验正交函数 (EOF) 分析，以表征地表风的日变化。前两个本征模态（EOF-1、EOF-2）（总方差的 58%）分别表征了 SYM 西部和东部的地表风变化。前两个时间系数（PC1、PC2）的频率分布的每小时百分位数用于识别三种类型的 Sundowner 状态。当地表风强烈投射到 EOF-1 (EOF-2) 而不是 EOF-2 (EOF-1) 时，就会出现西部（东部）状态。西部地区的特点是在 Point Conception 周围有强烈的沿海喷气机，西北风延伸到圣巴巴拉海峡。相比之下，在东部地区观察到没有延伸到圣巴巴拉海峡的弱沿海喷气机。在圣巴巴拉 (SBA) 地区，每小时的地表风在 EOF-1 和 EOF-2 上都强烈投射。西部政权比东部和 SBA 政权更频繁地发生，并且在 3-5 月达到高峰。东部制度在 1-2 月达到最大值，而 SBA 制度的季节性周期与西部制度相似。