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Atmospheric stability has a direct impact on how wind speed changes with height. Classic neutral-profile assumptions may therefore introduce biases unless they are corrected by stability-aware models.
To document how Vortex TIMES represents stability, Vortex carried out an atmospheric stability assessment with observational meteorological data supplied by Acciona, comparing atmospheric stability classes from both sources at an example site.
Stability was quantified with two metrics:
Both were grouped into a seven-class scheme, from Very Unstable to Very Stable, adapted from He et al. (2024) and optimised for wind energy applications.
The example site is onshore in South Australia, characterised by its local geography and land–sea contrasts. The analysis uses two levels, 60 m and 155 m.
The Vortex TIMES vertical wind profiles, grouped by stability class, show the direct impact of stability on wind shear. Under unstable conditions, enhanced vertical mixing produces more uniform profiles, with shear exponents of about 0.10–0.15. Near-neutral profiles approximate the logarithmic law (α ≈ 0.15–0.20). Under stable conditions, strong stratification results in pronounced shear (α ≈ 0.25–0.40+).
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The same diagnostics can be produced for other sites to evaluate how well the modelled data reproduce the local stability regime.
They group atmospheric conditions by their degree of vertical mixing. The scheme used in this study has seven classes, from Very Unstable (intense convection) through Neutral (mechanical turbulence dominates) to Very Stable (strong inversion and flow decoupling).
A dimensionless parameter that relates thermal stratification to wind shear in the atmospheric boundary layer. Negative values indicate convective conditions and vigorous thermal mixing, values near zero indicate near-neutral conditions, and large positive values indicate strong stratification and turbulence suppression.
RMOL is the reciprocal of the Monin–Obukhov length, a measure of surface-layer stability. It is very difficult to calculate without direct turbulent flux measurements, so it was used only for Vortex TIMES, which incorporates this variable from its WRF simulations.
In the Vortex TIMES profiles analysed, shear exponents were about 0.10–0.15 under unstable conditions, 0.15–0.20 under near-neutral conditions, and 0.25–0.40 or more under stable conditions.
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