The Sundowner Winds Experiment (SWEX) in Santa Barbara, CA: Advancing Understanding and Predictability of Downslope Windstorms in Coastal Environments

Abstract Coastal Santa Barbara is among the most exposed communities to wildfire hazards in southern California. Downslope, dry and gusty windstorms are frequently observed on the south-facing slopes of the Santa Ynez Mountains that separates the Pacific Ocean from the Santa Ynez Valley. These winds, known as “Sundowners”, peak after Sunset and are strong throughout the night and early morning. The Sundowner Winds Experiment (SWEX) was a field campaign funded by the National Science Foundation that took place in Santa Barbara, CA, between 1 April and 15 May 2022. It was a collaborative effort of ten institutions to advance understanding and predictability of Sundowners, while providing rich data sets for developing new theories of downslope windstorms in coastal environments with similar geographic and climatic characteristics. Sundowner spatiotemporal characteristics are controlled by complex interactions among atmospheric processes occurring upstream (Santa Ynez Valley), and downstream due to the influence of a cool and stable marine boundary layer. SWEX was designed to enhance spatial measurements to resolve local circulations and vertical structure from the surface to the mid-troposphere, and from the Santa Barbara Channel to the Santa Ynez Valley. This article discusses how SWEX brought cutting-edge science and the strengths of multiple ground-based and mobile instrument platforms to bear on this important problem. Among them are flux towers, mobile and stationary lidars, wind profilers, ceilometers, radiosondes, and an aircraft equipped with three lidars and a dropsonde system. The unique features observed during SWEX using this network of sophisticated instruments are discussed here.