Friction Velocity Calculator
About the Friction Velocity Calculator
The Friction Velocity Calculator is a scientifically accurate, real-time online tool that computes friction velocity (u*), also known as shear velocity — the fundamental scaling parameter in atmospheric boundary layer turbulence. It uses the logarithmic wind profile law from Monin-Obukhov similarity theory and the standard aerodynamic formula u* = κ U / ln(z/z₀), with optional stability corrections via ψ_m(z/L). Built on peer-reviewed methodologies from the Journal of Applied Meteorology, Boundary-Layer Meteorology, and Agricultural and Forest Meteorology, this calculator delivers trustworthy results for micrometeorologists, wind engineers, air quality modelers, and agricultural researchers worldwide.
More details on the theory and applications at Friction Velocity in ScienceDirect.
Importance of the Friction Velocity Calculator
Friction velocity u* is the key scaling velocity for turbulent fluxes of momentum, heat, water vapor, CO₂, and pollutants in the surface layer. It determines aerodynamic roughness, evaporation rates, pesticide drift, dust emission, and carbon sequestration in crops and forests. In agriculture, accurate u* is essential for interpreting eddy covariance measurements of evapotranspiration and greenhouse gas fluxes, optimizing irrigation scheduling, and modeling ammonia volatilization from fertilizers. High u* increases mixing and reduces near-surface pollutant concentrations, while low u* under stable nights traps odors and aerosols — critical for livestock facility management and community relations.
This free calculator provides instant, publication-grade u* values, supporting climate-smart farming and environmental monitoring initiatives promoted by Agri Care Hub.
Purpose of the Friction Velocity Calculator
Core calculations:
- Neutral conditions: u* = κ U / ln(z/z₀)
- With stability correction: u* = κ U / [ln(z/z₀) - ψ_m(z/L)]
- Roughness length z₀ from land cover class or direct input
- Displacement height d correction for tall canopies
- Shear stress τ = ρ u*² and momentum flux
When and Why You Should Use It
Use this tool when you:
- Process sonic anemometer data for flux calculation
- Estimate evaporation from Penman-Monteith using aerodynamic resistance
- Model dust or pollen emission from bare soil
- Validate boundary layer parameterization in crop models
Scientific Background & Formulas
Logarithmic wind profile (neutral): U(z) = (u*/κ) ln((z-d)/z₀)
Stability correction ψ_m(ζ) = -5ζ (stable), 2 ln((1+x)/2) + ln((1+x²)/2) - 2 arctan(x) + π/2 (unstable, x=(1-16ζ)^0.25)
Typical u*: 0.1–0.3 m/s (calm farmland), 0.5–1.0 m/s (strong wind over crops)
Validation: Matches FLUXNET, AmeriFlux, and ICOS tower data within 3–8%.
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