# Same simulated wind. Dust lifts only from sand.

At `u* = 0.2 m/s`, 10 µm dust lifted only from a thin layer over 100 µm sand grains. The pure-dust bed and the sand stayed still.

**In brief:** a grain-scale simulation shows how mixed-bed topography can expose fine dust to faster mean airflow. The result supports a mechanism, not a universal threshold for real deserts.

Primary source: [Kamath, Shao and Parteli, Communications Earth & Environment, 2026](https://doi.org/10.1038/s43247-026-03955-5).

## The controlled comparison

Figure 2a of the paper compares two beds at the same simulated friction velocity, `u* = 0.2 m/s`:

- pure 10 µm dust: does not lift;
- 10 µm dust over 100 µm sand: the dust lifts;
- 100 µm sand: stays still.

`u*` is friction velocity, a measure of airflow shear at the surface. It is not the wind speed in a weather app. In the model, stress is `τ = ρ_air · u*²`.

## Why height matters

Van der Waals attractions keep some fine grains on the surfaces of larger grains. In the model's prescribed mean wind profile, speed increases with height above the bed. Dust exposed higher up receives greater modeled drag and lift than dust near the low surface of a pure bed.

## Thresholds from the simulation

- `0.05 m/s`: the reported minimum threshold for 10 µm dust on the mixed bed;
- `≈0.25 m/s`: the threshold for 100 µm sand, five times higher;
- `≈one order of magnitude`: the pure-dust threshold relative to 0.05 m/s. The paper does not give an exact value for it in the text here.

These are simulation results. They should not be used as field thresholds without experimental validation.

## The decisive limit

The authors describe the bidisperse-bed result as qualitative. The model does not resolve local flow on the windward side of protruding grains, so it may overestimate speed and forces there. There is no comparable experimental measurement for this mixed bed yet. The real threshold reduction may be smaller than the roughly tenfold factor in the example.

The simulation uses spherical silica beads, a dry loose bed and the onset of direct entrainment. It does not include moisture, crusts, vegetation, electrostatic interaction forces, natural irregular shapes, the full size distribution or developed saltation transport.

Supplementary videos S1 and S2 use different geometries and different wind conditions. They are not the controlled comparison shown here.

## Sources

- [Article and Figure 2](https://www.nature.com/articles/s43247-026-03955-5)
- [Supplementary information](https://media.springernature.com/original/springer-static/esm/art%3A10.1038%2Fs43247-026-03955-5/MediaObjects/43247_2026_3955_MOESM2_ESM.pdf)
- [Transparent peer review](https://media.springernature.com/original/springer-static/esm/art%3A10.1038%2Fs43247-026-03955-5/MediaObjects/43247_2026_3955_MOESM1_ESM.pdf)
- [Additional-files description](https://media.springernature.com/original/springer-static/esm/art%3A10.1038%2Fs43247-026-03955-5/MediaObjects/43247_2026_3955_MOESM3_ESM.docx)

Published 28 August 2026. The source is licensed under [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/). Data are stated to be in the article and supplement; the authors' LAMMPS extensions are available on request.