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We introduce an analytical model that describes the vertical structure of Ekman boundary layer flows coupled to the Monin-Obukhov Similarity Theory (MOST) surface layer repre- sentation, which is valid for conventionally neutral (CNBL) and stable (SBL) atmospheric conditions. The model is based on a self-similar profile of horizontal stress for both CNBL and SBL flows that merges the classic 3/2 power law profile with a MOST-consistent stress profile in the surface layer. The velocity profiles are then obtained from the Ekman momentum balance equation. The same stress model is used to derive a new self-consistent Geostrophic Drag Law (GDL). We determine the ABL height (h) using an equilibrium boundary layer height model and parameterize the surface heat flux for quasi-steady SBL flows as a function of a prescribed surface temperature cooling rate. The ABL height and GDL equations can then be solved together to obtain the friction velocity (u∗) and the cross-isobaric angle (α0) as a function of known input parameters such as the Geostrophic wind speed and surface roughness (z0). We show that the model predictions agree well with simulation data from the literature and newly generated Large Eddy Simulations (LES). These results indicate that the proposed model provides an efficient and relatively accurate self-consistent approach for predicting the mean wind velocity distribution in CNBL and SBL flows.
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Baroclinicity and Stability in the Atmospheric Boundary Layer: Characterizing Their Interacting Effects via Large-Eddy Simulations and Reduced Models (Invited Presentation)
Baroclinicity adds another layer of complexity to the much-studied barotropic atmospheric boundary layers (ABLs) by modulating the pressure gradient in height. Despite the prevalence of baroclinicity in real-world ABLs, our knowledge of the interacting effects of baroclinicity and atmospheric stability is limited. In this talk, we aim to address this knowledge gap by systematically varying baroclinicity and stability using the large-eddy simulation (LES) technique. We will present how baroclinicity alters the friction velocity, Obukhov length, shear production, ABL height, and low-level jet (LLJ) in diabatic baroclinic atmospheric flows. It will be shown that while baroclinicity significantly impacts unstable, neutral, and weakly stable ABLs, its effects reduce with increased stratification in the ABL. In strongly stratified ABLs, the LLJ height, friction velocity, and Obukhov length converge to a constant asymptote independent of the baroclinicity regime. We will demonstrate that this behavior is attributed to the strong turbulence destruction in very stable ABLs that decouples the surface from higher elevations where baroclinicity is more important. Finally, two rescaling methods in the inner and outer layers of stable baroclinic ABLs will be presented to non-dimensionalize and collapse the wind profiles in baroclinic environments. The developed reduced model for different baroclinic wind profiles will be shown against the LES results. The findings of this research elucidate the underlying physics of baroclinic diabatic ABLs and are useful for characterizing the wind profiles in weather/climate models, field measurements, and various industrial applications.
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- Award ID(s):
- 2228299
- PAR ID:
- 10467585
- Publisher / Repository:
- https://ams.confex.com/ams/103ANNUAL/meetingapp.cgi/Paper/415405
- Date Published:
- Format(s):
- Medium: X
- Location:
- Denver, USA
- Sponsoring Org:
- National Science Foundation
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