Researchers K. Chand, Cheng-Nian Xiao, and Inanc Senocak from the University of Notre Dame have conducted a study to better understand the complex dynamics of stable atmospheric boundary layers, which are crucial for weather prediction and climate modeling. Their work, published in the Journal of Fluid Mechanics, focuses on the turbulent transport mechanisms in these layers, providing insights that could improve energy industry applications, such as wind energy and air quality management.
The researchers performed direct numerical simulations to examine how different factors influence turbulence within stable atmospheric boundary layers. They considered a four-dimensional parameter space defined by stratification mechanism and strength, wind-forcing, Rossby-radius factor, and Prandtl number. By creating a regime map, they identified three distinct regimes: linearly stable, very stable, and weakly stable. The weakly stable regime, characterized by persistent turbulence, emerged at low stratification and high wind-forcing conditions.
The study revealed that stable atmospheric boundary layers exhibit a multilayered thermal structure, comprising a near-surface stable layer, an intermediate unstable layer, and an overlying inversion. As stratification decreases, this structure strengthens, indicating enhanced downward heat transport. The researchers found that turbulence statistics, such as momentum field and turbulent kinetic energy, show weak dependence on stratification. However, buoyancy and turbulent potential energy exhibit strong sensitivity due to additional production from turbulent heat flux interacting with ambient stratification.
Energy transfer processes were also explored, highlighting the exchange among mean gradients, momentum-buoyancy flux, and turbulent kinetic energy-turbulent potential energy exchange. The turbulent Prandtl number, which relates eddy diffusivities for momentum and heat, showed strong vertical variation, exceeding typical values found in nocturnal stable atmospheric boundary layers. This underscores the limitations of constant eddy-diffusivity models currently used in many weather and climate models.
The study also employed barycentric anisotropy maps to analyze turbulence structure, revealing weak near-surface effects but enhanced isotropy aloft. These findings motivate the development of improved parameterizations for stable atmospheric boundary layers dominated by ambient stratification, which are essential for accurate weather prediction and climate modeling.
For the energy industry, a better understanding of these turbulent transport mechanisms can lead to more accurate wind resource assessment and forecasting, which are critical for the efficient integration of wind energy into the grid. Additionally, improved air quality management can be achieved through better prediction of pollutant dispersion in stable atmospheric conditions.
Source: Chand, K., Xiao, C.-N., & Senocak, I. (2023). Turbulent transport mechanisms in long-lived stable Ekman layers. Journal of Fluid Mechanics.
This article is based on research available at arXiv.