Spatial Heterogeneity in the Convective Boundary Layer Depth Observed during HI-SCALE

This study examines the spatial variability in the convective boundary layer (CBL) depth, zi, and its correlation with surface and subsurface conditions using an array of remote and in-situ sensors at the US Department of Energy’s Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site in north central Oklahoma. The SGP site is located in a region with a mix of crop land, pasture, and forest. The site consists of a distributed network of heavily instrumented sub-sites or facilities. Data from the central facility and four outlying boundary facilities are used to investigate the spatial heterogeneity in zi during the Holistic Interactions of Shallow Clouds, Aerosols, and Land-Ecosystems (HI-SCALE) experiment in the summer of 2016. The central and boundary facilities are contained within a region of roughly 75 km x 65 km in size, with the boundary facilities at the corners and the central facility at the center of the region.

At the central facility independent measurements of zi are obtained from radiosondes, a micropulse lidar (MPL), a Raman lidar and a Doppler lidar. These various zi measurements are compared. At the boundary facilities, where the instrumentation is more limited, measurements of zi are obtained from Doppler lidars. Different techniques are used to derive zi from the different instruments. For example, CBL heights from the radiosondes are estimated by locating the maximum vertical gradient in the potential temperature profile. For the Doppler lidars, we use two methods for identifying zi: One based on vertical velocity variance, and the other based on the vertical gradient of the attenuated backscatter. The latter method is also used to find zi from the MPL data. Additionally, we use water vapor mixing ratio from a Raman lidar to estimate zi.

The SGP site also contains an extensive array of 17 soil moisture and temperature sensors spread across the region as well as measurements of the surface energy fluxes, including the central and boundary facilities. Measurements of the daily maximum zi at the central and boundary facilities are compared with measurements of soil moisture, surface potential temperature tendency, and other surface/sub-surface variables. Results will be discussed.