Evaluating the Relative Contributions of Land Surface Fluxes toward Convective Boundary Layer Development at the ARM SGP Site: A Comparison of Observations and HRRR Output

The diurnal structure of the convective boundary layer (CBL) is highly sensitive to both surface and entrainment fluxes of moisture and energy. Evolution of the CBL can play a significant role in the development of shallow cumulus and convective precipitation during synoptically quiescent conditions. While operational mesoscale models continue to improve, it remains a challenge to represent these processes, many of which are subgrid-scale. Identifying sources of error within the land-atmosphere coupling process chain in the mesoscale model could lead to improved forecasts on days when the land surface plays a significant role in CBL development. Mixing diagrams are a useful tool for quantifying the relative contributions of surface, entrainment, and advective fluxes toward development of the CBL, and can be used with observational or model data. This study applied the mixing diagram framework to both observations and High Resolution Rapid Refresh (HRRR) numerical weather prediction model output to quantify land-atmosphere interactions at the ARM Southern Great Plains (SGP) site during the summer of 2017. Observations of vertical temperature and moisture profiles from multiple Atmospheric Emitted Radiance Interferometer (AERI) instruments captured the evolution of the CBL over locations with different land-cover types within the ARM SGP site. Surface flux observing platforms are co-located with each AERI instrument such that each location has observations of CBL structure and surface flux data at sub-hourly time scales and across heterogenous land surface conditions. Mixing diagrams were generated at each site to determine relative contributions of surface fluxes toward CBL development throughout the summer and across a diverse set of land surface conditions. These mixing diagrams were compared to those computed using output from the HRRR model at various forecast hours to determine when sources of error in HRRR representation of CBL development were tied to land surface characteristics.