Richard J.A.M. Stevens

Physics of Fluids

University of Twente

Publication 91 · Atmospheric turbulence

How stratification and rotation organize boundary-layer height

L. Liu, S.N. Gadde, and R.J.A.M. Stevens, Quarterly Journal of the Royal Meteorological Society 147(735), 847-857 (2021).

The article and Figure 4 are open access under CC BY 4.0.

Main finding

Across 24 idealized conventionally neutral atmospheric-boundary-layer LES, the dimensionless 5%-momentum-flux height |f|h/u* decreased systematically as the stratification-to-rotation ratio N/|f| increased from 42 to 1350. A curve fitted within the same simulation campaign organized the cases, while selected field estimates showed broad consistency rather than independent validation.

Dimensionless conventionally neutral boundary-layer height versus N divided by the magnitude of the Coriolis parameter for three free-atmosphere lapse rates and selected field estimates
How to read the figure. The vertical axis is the diagnosed 5%-momentum-flux height made dimensionless with the Coriolis frequency |f| and friction velocity u*. The horizontal axis, μN = N/|f|, compares free-atmosphere stratification with rotation. Squares, circles, and triangles are LES at lapse rates of 1, 3, and 9 K km−1; red stars are selected field estimates. The solid curve is fitted within the present LES campaign, whereas the dashed curve and pink band show an earlier model. The downward trend supports a compact organization of the tested cases, but the same-data fit and uncontrolled field differences do not establish independent or universal validation. Open the full-resolution figure. Figure 4, cropped without resampling. L. Liu, S.N. Gadde, and R.J.A.M. Stevens (2021), CC BY 4.0.

Why this matters

A zero surface heat flux does not make an inversion-capped atmospheric boundary layer dynamically identical to a truly neutral layer. Free-atmosphere stratification limits the layer from above while planetary rotation sets a competing time and length scale. Their ratio therefore provides a physically motivated coordinate for organizing the layer height and, in the wider paper, the empirical coefficients entering the geostrophic drag law.

Research context

The main campaign contains 24 wall-modelled LES in a flat, horizontally periodic 2π km × 2π km × 2 km domain. It fixes the geostrophic wind at 12 m s−1 and roughness length at 10−4 m while varying latitude from 5° to 70° and free-atmosphere lapse rate from 1 to 9 K km−1. The simulations use a traditional f-plane, zero surface heat flux, uniform geostrophic wind, and no baroclinicity, terrain, roughness heterogeneity, or transient forcing. The height and drag-law curves are calibrated on the same LES matrix; no fit covariance or held-out numerical test is supplied. Endpoint grid and subgrid-model checks preserve the main trend but do not establish absolute convergence, and the selected field data do not control measurement uncertainty, roughness, nonstationarity, or thermal-state differences. The result is therefore a regime-specific empirical organization, not a universal boundary-layer-height law or a direct wind-energy-performance prediction.

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