Observing mountain waves and impacts on surface winds over eastern Santa Ynez Mountains in Santa Barbara, CA, during the Sundowner Winds Experiment (SWEX): A Case Study
- de Orla-Barile, Marian
- Advisor(s): Carvalho, Leila
Abstract
The southern-facing coastal plain of Santa Barbara County (CA) 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. Due to its proximity to these complex features, this region commonly experiences a gusty, northerly, downslope flow known locally as Sundowner Winds or simply Sundowners. Named for their typical time of onset (i.e. sunset), Sundowners have been involved in many of the wildfires which have affected communities living along the Santa Barbara coastal plain. Thus, improved forecasts of the intensity and spatiotemporal variability of these winds are necessary to prevent and prepare for wildfire influenced disasters. In order to study the mesoscale mechanisms responsible for Sundowners, a multi-institution field campaign, termed the Sundowner Wind Experiment (SWEX), was completed over April-May of 2022 across Santa Barbara County. This study examines observations from various meteorological instruments, with a particular focus on conditions over the eastern SYM, during the final intensive observation period (IOP) of the SWEX campaign. This IOP (IOP #10) occurred over a 24-hour period beginning on May 12, 2022 at 10:00PDT (17:00UTC). Synoptic scale analysis during IOP #10 shows zonal flow at upper levels of the atmosphere (i.e. 500hPa) occurring alongside a steep, west-east oriented mean sea level pressure gradient that developed as a result of a high pressure system offshore of California and comparatively lower pressure over the US mainland, supporting a primarily surface pressure driven Sundowner event. Results from three ground-based light detection and ranging (LiDAR) wind profilers, situated within the slopes along and foothills below the eastern SYM, reveal strong differences in horizontal wind speeds between stations. The highest wind speeds and associated turbulence, as revealed by a series of radiosonde launches, occur near the easternmost portion of the SYM, in the city of Montecito. Common surface meteorological variables (e.g. air temperature, dewpoint, and winds) from previously established local weather station networks, as well as from specific surface stations deployed during the SWEX campaign, are used to add additional context to the evolution of Sundowner conditions during IOP #10 across the study domain. The results presented here aim to contribute pertinent information to the operational forecasting community regarding the connection between surface and upper-level atmospheric conditions during a particular Sundowner event over a region that has experienced numerous instances of destructive Sundowner blown wildfires.