SAVANT: A Field Campaign for the Stable Boundary Layer

Stable boundary layers are still a relatively problematic component of atmospheric modeling, despite their frequent occurrence. While general agreement exists that MO similarity is not applicable in the SBL due to the non-homogeneous, non-stationary flow, no universal organizing theory for the surface SBL has been presented. This poses a problem when examining aerosol movement as a function of atmospheric dynamics. It is known that stable air stratification results in katabatic downslope winds, even in very shallow topographic airsheds. These downslope winds can converge with background flow, and it is hypothesized that this convergence provides a starting point for specific events, such as internal gravity waves. Even though the stable boundary layer is normally shallow, internal gravity waves can propagate at an angle from the horizontal plane, and modify local shear, thus generating periodic turbulent mixing in space. Some studies have measured converging background and drainage flows in mountain areas, however, few studies have examined this in less dramatic, but more common, topographic areas. We propose a measurement campaign to address these open issues. The Stable Atmosphere Variability ANd Transport (SAVANT) field program aimed to address these issues through quantification of the effects of shallow cold air drainage on aerosol transport and dispersion. We hypothesize that converging flows, which we define as flow from cold-air drainage merging into an area of relatively slower and less turbulent air (i.e. the background flow), will only occur under certain, identifiable, mesoscale synoptic conditions. We also hypothesize that the intense and sudden shear formed at the point of convergence will generate turbulence forced or gravity waves which in turn affect dispersion. The measurement campaign took place September 15 to November 15 2018. The field campaign consist of point and area releases of aerosols along a shallow gully measured with two 3-D aerosol lidars, as well as a full characterization of the 3-D wind field and turbulence, spatial atmospheric pressure and temperature by tower and Doppler lidar observations. This presentation will provide an overview of the field campaign, and preliminary results from early nights of intensive operations. The novel aspect of this work is the ability to identify turbulent events and features with aerosol lidars to add the missing spatial component to our current understanding.