Differences in Simulated and Observed Variability of Surface Broadband and Spectral Albedo Over the SGP

Description

The surface exchange of heat, moisture, and momentum is controlled by the net radiation at the surface. The surface albedo is one important factor in the net short-wave radiation budget and it is an important source of bias in simulated near-surface temperature. The U.S. Department of Energy’s (DOE) Holistic Interactions of Shallow Clouds, Aerosols, and Land-Ecosystems (HI-SCALE) campaign provides the opportunity to study both the broadband and spectrally resolved surface albedo around the ARM Southern Great Plains site over the course of a growing season. Airborne measurements, made using upward and downward looking Delta-T Devices SPN-1 broadband radiometers and multi-filter radiometers (MFR) on the DOE Gulf Stream 1 (G-1), are used to compute the broadband and spectral albedo and the Normalized Difference Vegetation Index (NDVI), after correction for tilt from horizontal. There are some differences in albedo between the spring and fall, which can be attributed to both changes in the soil moisture and vegetation. The measurements show significant spatial variations in the surface broadband albedo for an area within approximately 40 kilometers of the DOE Atmospheric Radiation Measurement (ARM) Central Facility. This spatial variability is severely underestimated in a series of WRF simulations completed using the Noah land-surface model, which could mute the spatial variability in the simulated surface fluxes compared to observations. There are large seasonal differences in NDVI, associated with generally greener ground cover during the spring study period and there is a great deal of fine-scale spatial variability of NDVI in the vicinity of the ARM site. We will also highlight how HI-SCALE results can be used to evaluate the performance of routine data products developed by the DOE ARM User Facility, and satellite derived values of surface albedo.