Atmospheric Boundary Layer Height Calculator

This calculator uses fast parameterizations based on the Coriolis parameter: f = 2Ω sin(φ), where Ω is Earth’s rotation rate and φ is latitude.

• Mechanical / stable estimate: h = C · u* / |f|
• Convective estimate: zᵢ = C · w* / |f|

The coefficient C is adjustable because conditions vary. Near the equator, |f| becomes small and the estimate can be unreliable.

1. Select an estimation method that matches your stability.
2. Enter latitude to compute the Coriolis parameter.
3. Provide u* for mechanical or w* for convective.
4. Adjust the coefficient if you have local calibration.
5. Click Calculate to see the result above.
6. Use the download buttons to export CSV or PDF.

• Typical daytime mixed layers range from ~300 to 3000 m.
• Stable nighttime layers can be much shallower, often under 500 m.
• Terrain, clouds, and mesoscale flows can dominate real height.
• For rigorous work, use radiosonde profiles or lidar retrievals.

1) Why boundary layer height matters

The atmospheric boundary layer (ABL) is the lowest part of the troposphere that responds to surface forcing within about an hour. Its height controls pollutant dilution, wind‑energy yield, dispersion modeling accuracy, and the depth of daytime mixing that shapes temperature and humidity profiles.

2) Typical ranges you may observe

Over land, a convective daytime ABL often grows from a few hundred meters after sunrise to roughly 1–3 km by mid‑afternoon, depending on heating and entrainment. Stable nighttime layers are commonly shallow, frequently under 500 m, with intermittent turbulence and strong stratification.

3) Two fast estimation pathways

This calculator provides two parameterized options: a mechanical pathway based on friction velocity (u*) for shear‑driven turbulence, and a convective pathway based on the convective velocity scale (w*) for buoyancy‑driven turbulence. Both approaches relate a velocity scale to Earth’s rotation via the Coriolis parameter.

4) What the inputs represent

Latitude sets the Coriolis parameter f, typically around 10⁻⁴ s⁻¹ at mid‑latitudes. Friction velocity u* summarizes near‑surface stress; many field sites report 0.1–1.0 m/s depending on roughness and wind. The convective scale w* often spans 0.5–3.0 m/s on sunny, well‑mixed afternoons.

5) Role of adjustable coefficients

Coefficients allow calibration to local conditions and model conventions. Values around 0.20–0.40 are commonly used in simplified scaling studies. If you have tower or radiosonde diagnostics, tune the coefficient so typical cases match observed layer depths.

6) Data quality and sensitivity

Because the estimate scales with 1/|f|, it becomes sensitive near the equator where |f| is small. Small errors in u* or w* also propagate linearly to height. Use averaged inputs (10–30 minutes) rather than instantaneous spikes when possible.

7) Interpretation for air quality and weather

A deeper ABL generally increases dilution volume and can reduce near‑surface concentrations, while shallow stable layers favor accumulation and sharp gradients. For forecasting, compare the height trend across the diurnal cycle rather than relying on one value, especially during transitions.

8) When to use more advanced methods

For high‑stakes dispersion or research, derive ABL height from radiosonde potential temperature profiles, lidar backscatter, or turbulence retrievals. Use this calculator as a rapid screening tool, a consistency check, or a way to standardize quick reports.

1) Which method should I choose?

Use the mechanical method for stable or shear‑dominated conditions. Use the convective method for sunny, buoyant, well‑mixed periods when w* is available.

2) Why does latitude affect the result?

Latitude sets the Coriolis parameter, which represents rotational influence. The estimate scales with 1/|f|, so the same turbulence intensity implies a deeper layer where |f| is smaller.

3) What if I am near the equator?

Near 0° latitude, |f| becomes very small and simple scaling can overestimate height. Prefer observation‑based methods or use a site‑specific model rather than this quick estimate.

4) What are reasonable values for u*?

Many land sites fall near 0.1–1.0 m/s, increasing with wind speed and surface roughness. Use an averaged value from sonic anemometer processing if you have it.

5) What are reasonable values for w*?

Typical convective w* values range from about 0.5–3.0 m/s during strong daytime heating. If you lack w*, choose the mechanical method or estimate w* from surface heat flux.

6) How should I set the coefficient?

Start with 0.30 for mechanical and 0.20 for convective, then adjust using local observations. A single calibrated coefficient can improve repeatability across seasons at one site.

7) Does this replace radiosonde or lidar ABL height?

No. This is a parameterized estimate for quick screening and reporting. Profile‑based methods capture inversions, residual layers, and entrainment that simple scaling cannot represent.