Over three decades, and counting, of near-surface turbulent flux measurements from the Atmospheric Radiation Measurement (ARM) user facility

Abstract. Processes mediating the coupling of terrestrial, aquatic, biospheric, and atmospheric systems influence weather, climate, and ecosystem dynamics via transfer of energy, momentum, water, and carbon (or other species). These exchange processes are quantified by measurements of near surface turbulent fluxes. Understanding processes at these interfaces provides insight into understanding and predicting current and future states within the Earth system. The Atmospheric Radiation Measurement (ARM) user facility has been conducting measurements of near surface turbulent fluxes since the early 1990's at long term fixed locations and shorter-term, mobile deployments across the Earth. ARM has utilized two established methods for conducting these measurements, energy balance Bowen ratio (EBBR) and eddy covariance (EC). Primary measurements from the former include sensible and latent heat flux, while the latter also measures fluxes of momentum and carbon (primarily carbon dioxide, with methane fluxes measured at select (two to date) locations). The EBBR systems were deployed at 22 locations, and to date, the EC systems have been deployed at over 50 sites with plans for additional novel site locations into the future. Herein, the history, evolution, and key aspects of these instrument systems are documented, along with information on data quality assurance and post-processing, and best use practices. Additionally, three recent data validation experiments were conducted, and their key findings are summarized. Finally, ancillary datasets acquired by ARM, that can contextualize and aid interpretation of the near surface turbulent flux measurements, are discussed.

Datasets described herein include the eddy correlation flux measurement system: 30ECOR (https://doi.org/10.5439/1879993, Sullivan et al., 1997), 30QCECOR (https://doi.org/10.5439/1097546, Gaustad 2023), and ECORSF (https://doi.org/10.5439/1494128, Sullivan et al., 2019a); the energy balance Bowen ratio system: 30EBBR (https://doi.org/10.5439/1023895, Sullivan et al., 1993) and 30BAEBBR (https://doi.org/10.5439/1027268, Gaustad and Xie 1993); and the carbon dioxide flux measurement system: CO2FLX (https://doi.org/10.5439/1287574, https://doi.org/10.5439/1287575, https://doi.org/10.5439/1287576, Koontz et al., 2015a,b,c). These data can be found by searching the above datastream names at https://adc.arm.gov/discovery/#/results/.