Investigating the spatial structure of winds in complex terrain using a mobile wind lidar

In the lee of the Santa Ynez Mountains north of Santa Barbara, CA, late afternoon-to-early morning episodes of offshore, northerly gusty downslope surface winds are frequently observed. These downslope winds are locally known as Sundowners. Sundowners are spatially non-uniform and can be accompanied by rapid increases in temperature and decreases in relative humidity with significant impact on fire behavior. Our understanding of the spatial and temporal variability of Sundowners and the underlying mesoscale mechanisms is limited. To address this knowledge gap, the NSF-funded Sundowner Wind Experiment (SWEX) was conducted in Spring 2022.  

In this presentation, we focus on observations made by the surface-based mobile observing platform UWOW (University of Virginia Wind Observatory on Wheels), a trailer-mounted lidar system to measure spatial and temporal variations of lower tropospheric winds.  UWOW uses a HALO photonics StreamLine XR Doppler lidar, a GPS, and an inertial navigation system placed in a custom trailer to measure boundary layer winds while traveling on the road. UWOW can measure wind profiles from approximately 100 to 3000 m above ground with 30 m vertical spacing. During SWEX, UWOW travelled about 7000 km on roads around the Santa Ynez Mountains to document the spatial wind and aerosol variability during Sundowner Wind days and during undisturbed days. Data examples and comparisons with 1-km numerical simulations using the Weather Research and Forecasting (WRF) model will be discussed.