Climatology of Sundowner winds in coastal Santa Barbara, California, based on 30 yr high resolution WRF downscaling
Climatology of Sundowner winds in coastal Santa Barbara, California, based on 30 yr high resolution WRF downscaling
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DOI：
10.1016/j.atmosres.2020.105305
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发表时间：
2021-02
影响因子：
5.5
通讯作者：
Charles Jones;L. Carvalho;G. Duine;K. Zigner
中科院分区：
文献类型：
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作者：
Charles Jones;L. Carvalho;G. Duine;K. Zigner
日落风是一种下坡风暴，在加利福尼亚州南部圣巴巴拉的圣伊内斯山脉（SYM）的南山坡上观察到。“日落者”这个名字是由于在日落时强风的开始。日落风可以达到大风的强度，在野火中是非常危险的。本文介绍了一个基于天气研究与预报模式获得的30年高时空分辨率数据集的日落者气候学。结合经验正交函数（EOF）分析了在1 km栅格间隔下每小时纬向风和经向风（10 m）的变化特征。前两个特征模态（EOF-1和EOF-2）（占总方差的58%）分别表征了SYM西部和东部地面风的变率。前两个时间系数（PC1, PC2）频率分布的每小时百分位数用于识别三种类型的日落状态。当地面风在EOF-1 （EOF-2）上投射强烈而在EOF-2 （EOF-1）上投射不强烈时，就会出现西（东）风。西部地区的特点是一股强大的沿海急流围绕着森普辛点，西北风延伸到圣巴巴拉海峡。相反，在东部地区观察到一个弱的沿海急流没有延伸到圣巴巴拉海峡。在圣巴巴拉（SBA）地区，每小时地面风在EOF-1和EOF-2上都有强烈的投射。西部地区比东部和SBA地区发生频率高，在3 - 5月达到高峰。东部气旋在1 - 2月最大，而SBA气旋的季节周期与西部气旋相似。风和位温的水平和垂直结构表明，在三种情况下，SYM上的背风坡急流和山波活动表现出强烈的空间变化。
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.