Areal-Averaged Surface Albedo Product Now Baseline

Four plots are stacked from top to bottom, showing estimated surface albedo, cloud type, cloud optical depth, and precipitation. — This ArealAveAlb quicklook image from the EPCAPE campaign in La Jolla, California, provides the estimated surface albedo at the five multifilter rotating shadowband radiometer frequencies (top). Because of albedo’s sensitivity to cloud cover and precipitation, plots of input data—cloud type, cloud optical depth, and precipitation—are also included underneath the albedo plot. Image is provided by Krista Gaustad, Pacific Northwest National Laboratory.

The Atmospheric Radiation Measurement (ARM) User Facility’s Areal-Averaged surface Albedo value-added product (ArealAveAlb VAP) is now a baseline product, meaning it has moved from evaluation to production. Production or baseline VAPs are reviewed and verified as compliant with ARM data standards and are processed automatically or manually on ARM production servers.

The first ArealAveAlb production data are from two recent ARM field campaigns: the 2021–2023 Surface Atmosphere Integrated Field Laboratory (SAIL) campaign near Crested Butte, Colorado, and the 2023–2024 Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE) in La Jolla, California.

ArealAveAlb retrieves areal-averaged surface albedo under overcast conditions from ground-based measurements of solar radiation at four wavelengths—500, 615, 675, and 870 nanometers (nm)—for snow-free surfaces and areas partly covered by snow. Surface albedo, defined as the ratio of irradiance reflected from a surface to the downwelling irradiance, is vital for understanding Earth’s energy balance.

The multifilter rotating shadowband radiometer (MFRSR) measures downwelling solar radiation at ARM fixed-location and mobile sites. The MFRSR’s spectrally resolved measurements have been instrumental in retrieving cloud properties, such as cloud optical depth. An approach developed by Barnard et al. (2008) established an analytical link among cloud optical depth, surface albedo, and asymmetry factor using atmospheric transmission measured by the MFRSR at ARM sites under overcast conditions. ArealAveAlb extends this retrieval methodology by integrating additional information, such as cloud base height and cloud type, to improve the accuracy of areal-averaged surface albedo estimates.

If tower-based measurements are unavailable, the VAP uses an assumed surface albedo of 0.04 at 415 nm (Kassianov et al. 2014), representing a snow-free surface. Tower measurements are not available at ARM’s mobile facilities, so the areal-averaged albedo for SAIL and EPCAPE is only reported when the surface is snow-free.

The ArealAveAlb VAP requires an estimate of the surface albedo at 415 nm. For sites at which tower-based measurements are available, those values are used.

ArealAveAlb production data are now available for SAIL from September 1, 2021, through June 15, 2023, and EPCAPE from February 17, 2023, through February 14, 2024. These data are available in netCDF format.

Existing ArealAveAlb evaluation data for ARM’s Eastern North Atlantic and Southern Great Plains atmospheric observatories will be reprocessed to baseline in the relative near term.

More information about ArealAveAlb, including the technical report, is available on the VAP web page. For questions or to report data issues, please contact ARM translator Damao Zhang.

Access the data in the ARM Data Center. (To download the data, first create an ARM account.)

To cite the ArealAveAlb data, please use doi:10.5439/1209102.

References:

Barnard JC, CN Long, EI Kassianov, SA McFarlane, JM Comstock, M Freer, and G McFarquhar. 2008. “Development and evaluation of a simple algorithm to find cloud optical depth with emphasis on thin ice clouds.” Open Atmospheric Science Journal 2, 46-55, https://doi.org/10.2174/1874282300802010046

Kassianov E, J Barnard, C Flynn, L Riihimaki, J Michalsky, and G Hodges. 2014. “Areal-averaged and spectrally-resolved surface albedo from ground-based transmission data alone: Toward an operational retrieval.” Atmosphere 5(3), 597-621, https://doi.org/10.3390/atmos5030597