Insights on the Spatiotemporal Variability of Downslope Winds in Coastal Santa Barbara: A Case Study from the Sundowner Winds Experiment (SWEX)

Abstract The coastal plain of Santa Barbara County (SBC) is bounded by the cool waters of the Pacific Ocean to the south and the west–east-oriented Santa Ynez Mountains (SYM) to the north. Downslope windstorms with a typical onset after sunset are frequently observed on the lee slopes of the SYM. These northerly winds are known as Sundowner winds or simply Sundowners. The Sundowner Winds Experiment (SWEX), conducted between 1 April and 15 May 2022, aimed to unravel mechanisms responsible for the spatiotemporal variability of these winds. The present study examines data collected from lidar wind profilers, radiosondes, and surface stations during the 12–13 May 2022 intensive observation period (IOP). Gusty winds were observed on both the western and eastern slopes of the SYM. This event was associated with the second-largest observed mean sea level pressure difference between the Santa Barbara and Bakersfield airports during SWEX. However, horizontal wind speeds exceeding 20 m s −1 were recorded on the eastern slopes of the SYM hours before the most pronounced observed pressure differences. Furthermore, lidar measurements in the foothills of the eastern SYM exhibited positive vertical wind speeds of approximately 6 m s −1 . These ascending vertical motions were associated with the lifting of the lee-slope jet and a concurrent weakening of winds near ground level—a clear indication of mountain-wave activity influencing surface winds. While mesoscale numerical simulations with 1-km grid spacing captured the spatial patterns of the winds, their temporal variability was inadequately represented in highly turbulent regions.