Spatial correlation between mixed layer depth and surface properties at SGP

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Description

Understanding the spatial and temporal variability in the planetary boundary layer (PBL) height, zi, is key to improving the skill of climate, weather and air quality models in representing near-surface turbulent mixing, entrainment across the PBL top, and the cloud-base height of shallow convection. To address this and other issues, the ARM program recently (2016) installed four PBL profiling facilities (i.e. boundary facilities) at the Southern Great Plains (SGP) site to augment the already substantial instrumentation at the SGP central facility. The central and boundary facilities are each equipped with Doppler lidars (DLs), Atmospheric Emitted Radiance Interferometers (AERIs), surface meteorological stations, microwave radiometers, flux stations, soil moisture sensors, and other instrumentation. Additionally, radiosondes are launched four times daily from the SGP central facility. These observational capabilities enable routine monitoring of the PBL over a region of roughly 75 km x 65 km in size. In this study, we use observations from the SGP PBL profiling network to examine the spatial variability in the convective boundary layer (CBL) depth, and its correlation with surface and subsurface parameters including soil moisture, surface albedo, latent and sensible heat flux, TKE, evaporative fraction and many other parameters. The analysis is conducted using 378 days with clear or shallow cumulous conditions spanning the warm seasons (May through September) for the years 2016 through 2018. This includes the Holistic Interactions of Shallow Clouds, Aerosols, and Land-Ecosystems (HI-SCALE) experiment in 2016, and the Land-Atmosphere Feedback Experiment (LAFE) in 2017. Spatial correlations between the daily maximum zi from the Doppler lidar and various surface parameters reveal that zi is significantly anti-correlated with soil moisture. Daily correlations are strongest (most negative) between June and August, where the mean daily spatial correlation was found to be -0.5. By contrast, the mean daily spatial correlation for May and September was -0.1 and -0.3, respectively. In addition to soil moisture, we also present results on the spatial correlation between the daily maximum zi and the black sky albedo data product from MODIS.