What is the power law wind profile?

The power law (Hellmann equation) models how wind speed increases with height: V2 = V1 × (H2 / H1)^α. V1 is the known speed at reference height H1, V2 is the estimated speed at target height H2, and α (alpha) is the surface roughness exponent.

What Hellmann exponent should I use?

Common values: 0.10–0.13 for open water or flat coastal areas, 0.14–0.16 for flat open terrain (standard met mast default is 1/7 ≈ 0.143), 0.20–0.25 for agricultural land with scattered trees, 0.25–0.30 for forests and suburbs, 0.30–0.40 for urban centers with tall buildings.

What is the standard Hellmann exponent?

The most widely used default is 1/7 (≈ 0.143), which approximates neutral atmospheric stability over flat, open terrain — the same assumption used in many wind energy standards.

Does this account for atmospheric stability?

No. The power law is a simplified model that assumes neutral atmospheric stability. For stable or unstable conditions (e.g., strong daytime heating or nighttime inversions), the logarithmic wind profile or Monin–Obukhov similarity theory gives more accurate results.

Why does wind speed increase with height?

Surface friction from terrain features slows wind near the ground. This friction effect decreases with altitude, so wind speed generally increases with height up to the top of the atmospheric boundary layer (roughly 1–2 km).

Wind Shear Calculator

Name: Wind Shear Calculator
Availability: InStock
Author: Nham Vu

Estimate wind speed at any height using the power law wind profile and a terrain roughness (Hellmann) exponent.

Inputs

Reference wind speed (V₁)

m/s

Reference height (H₁)

Target height (H₂)

Terrain type (Hellmann exponent α)

Wind Speed at Target Height

—

Enter values and press Calculate

Formula Breakdown

Speed vs Height Profile

Height (m)	Wind Speed (m/s)	vs. Reference

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Summary

Estimate wind speed at any height using the power law wind profile and a terrain roughness (Hellmann) exponent.

How it works

Enter the known wind speed at a reference height (e.g., 10 m anemometer height).
Enter the reference height in meters.
Enter the target height at which you want to know the wind speed.
Select or enter the Hellmann terrain roughness exponent for your surface type.
The calculator applies the power law formula: V2 = V1 × (H2 / H1)^α.
Results show the estimated wind speed at the target height instantly.

Use cases

Wind energy: estimate hub-height wind speed from met-mast measurements.
Aviation: assess low-level wind shear risk for takeoff and landing.
Structural engineering: determine wind loads at building or tower heights.
Meteorology: model wind profiles over varying terrain types.
Drone and UAV operations: plan safe operating altitudes.
Environmental impact assessments for tall structures.

Frequently Asked Questions

Last updated: 2026-06-15 · Reviewed by Nham Vu