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ARS Home » Southeast Area » Jonesboro, Arkansas » Delta Water Management Research » Research » Publications at this Location » Publication #360643
Research Project: Preserving Water Availability and Quality for Agriculture in the Lower Mississippi River Basin

Location: Delta Water Management Research

Title: Friction velocity estimates using the trace of a scalar and the mean wind speed

Author
item CASTELLVI, F - Universitat De Lleida
item SUVOCAREV, K - University Of Arkansas
item Reba, Michele
item RUNKLE, B.R.K. - University Of Arkansas

Submitted to: Boundary Layer Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2020
Publication Date: 4/20/2020
Citation: Castellvi, F., Suvocarev, K., Reba, M.L., Runkle, B. 2020. Friction velocity estimates using the trace of a scalar and the mean wind speed. Boundary Layer Meteorology. 176(1):105-123. https://doi.org/10.1007/s10546-020-00520-1.
DOI: https://doi.org/10.1007/s10546-020-00520-1

Interpretive Summary: Determining the roughness length for momentum and friction velocity are important micrometeorological parameters that can be expensive and inaccurate to determine. This study tests a new theoretical basis for the surface renewal method of micrometeorology that investigates the smallest eddies. This method, when applied with high frequency scalar traces of water vapor or CO2 concentration, can be used to derive the roughness length for momentum and friction velocity. This method has advantages over some current methods, namely its accuracy and its affordability. Improved determination of these parameters will help land surface modeling of agricultural systems. This information is important to improve global land surface modeling.

Technical Abstract: A formulation based on Surface Renewal theory and analysis of the Smallest Eddies (SRSE) for estimating the friction velocity (u_*) is presented for measurements taken in the inertial sub-layer. SRSE requires the mean wind speed and the trace of the air (or sonic) temperature as input and here it has been extended to traces of water vapor (H2O) and carbon dioxide (CO2) concentrations. SRSE was compared against the Eddy Covariance (EC) method over a changing surface (a growing cotton field that included bare soil with some cover crop residues at the beginning of the season). Estimates of the roughness length for momentum (z0m) were determined from a combination of SRSE and EC with the conventional Wind Profile (WP) formulation under neutral conditions. For unstable and neutral cases, SRSE u* and z0m performed close to the reference for periods when mean wind speeds higher than 1 m s 1 (at 3 m above the ground) prevailed. For light winds, in practice, the additional input requirement was the canopy height. For stable cases, when stability corrections were included in SRSE the correlation with EC improved except the relative root mean square error. Regardless of the atmospheric conditions, SRSE using traces of water vapor concentration measured at 10 Hz may perform even closer to EC than WP. CO2 high frequency traces did not perform as well as for H2O likely a consequence of the contrasting source strength, but this issue remained unclear. Using traces of temperature, SRSE becomes an affordable and advantageous method to estimate friction velocities.