Scenario comparison
Compare dry sensible-heat cases. Values use SI units and upward-positive heat flux.
| Name | u* (m/s) | H (W/m²) | Temperature (°C) | Density (kg/m³) | Height (m) | L (m) | z/L | Class | Action |
|---|
CSV columns: name, uStar, heatFlux, temperatureC, density, height.
Sensitivity charts
Charts use the sensible heat-flux equation and current sensible-mode values.
Formula used
Virtual-flux form: L = −u*³θv ÷ (κg w′θv′).
Dry sensible-heat form: L = −ρcpθu*³ ÷ (κgH).
Dimensionless stability: ζ = z/L.
Stress-derived friction velocity: u* = √(|τ|/ρ).
How to use
- Select the calculation method matching your available measurements.
- Choose the heat-flux sign convention used by your dataset.
- Enter all measurements and confirm their displayed units.
- Open the constants panel only when nonstandard values are required.
- Submit the form and review stability, warnings, and calculation steps.
- Export results or compare additional dry sensible-heat scenarios.
Example data
| Condition | u* (m/s) | H (W/m²) | Temperature | Density | Height | Expected sign |
|---|---|---|---|---|---|---|
| Sunny daytime | 0.35 | 120 | 25°C | 1.18 kg/m³ | 10 m | L negative |
| Clear nighttime | 0.20 | −35 | 12°C | 1.23 kg/m³ | 5 m | L positive |
| Near-neutral windy | 0.65 | 1 | 18°C | 1.21 kg/m³ | 10 m | |L| very large |
Assumptions and limitations
Monin–Obukhov similarity is intended for the atmospheric surface layer. It assumes approximately stationary, horizontally homogeneous conditions over suitable terrain. Complex terrain, strong advection, rapid transitions, and very large stability magnitudes can reduce reliability.
The sensible heat mode treats thermal effects as dry buoyancy. Use moist-air mode when latent heat and humidity are important. Profile mode is an approximate screening method, not a replacement for measured turbulent fluxes.
Frequently asked questions
What does a negative Monin–Obukhov length mean?
A negative L generally indicates unstable, convective conditions. Upward buoyancy supports turbulence and vertical mixing.
What does a positive length mean?
A positive L indicates stable stratification. Buoyancy suppresses turbulent exchange and vertical motion.
Why is z/L more useful than L alone?
The stability parameter includes measurement height. It therefore expresses stability relative to the observation level.
What happens when heat flux equals zero?
The calculated length approaches infinity. Its reciprocal and z/L approach zero, representing neutral conditions.
Which calculation mode is most accurate?
The virtual potential temperature flux mode is preferred when reliable turbulence flux measurements are available.
Can friction velocity be calculated from stress?
Yes. The calculator combines stress components and applies u* = √(|τ|/ρ).
When should moist-air mode be used?
Use it when humidity and latent heat materially affect buoyancy, especially over wet or vegetated surfaces.
Why can profile mode differ from flux mode?
Profile estimates depend on empirical mappings and finite differences. Flux methods measure turbulent transport more directly.
Can the result be used over complex terrain?
Use caution. Slopes, buildings, coastlines, and roughness transitions can violate horizontal homogeneity assumptions.