Monin-obukhov similarity theory

Definition

Monin-Obukhov similarity theory is a foundational concept in boundary layer meteorology that describes the relationship between turbulence, temperature, and wind speed in the atmospheric boundary layer. It provides a framework for understanding how surface heat flux influences the structure of the atmosphere close to the Earth's surface, integrating both stable and unstable atmospheric conditions.

5 Must Know Facts For Your Next Test

1. Monin-Obukhov similarity theory relies on a dimensionless scaling approach, where parameters are normalized to reflect stability conditions in the atmosphere.
2. The theory introduces the concept of the Monin-Obukhov length scale, which indicates the relative influence of buoyancy and mechanical turbulence in determining flow characteristics.
3. In unstable conditions, turbulence is driven primarily by thermal buoyancy, while in stable conditions, wind shear becomes more dominant.
4. The theory suggests that vertical profiles of wind speed and temperature can be expressed using universal functions, simplifying predictions across different atmospheric conditions.
5. Applications of this theory include weather forecasting, climate modeling, and understanding pollutant dispersion in the atmosphere.

Review Questions

• How does Monin-Obukhov similarity theory apply to understanding turbulence within the atmospheric boundary layer?
  • Monin-Obukhov similarity theory connects turbulence in the atmospheric boundary layer to surface heat flux and wind speed through dimensionless scaling. It shows that turbulent flow characteristics can be predicted based on stability conditions—whether the atmosphere is stable or unstable. By relating variables like temperature and wind speed through universal functions, it helps meteorologists understand how energy and momentum are transferred from the surface into the atmosphere.
• What role does the Monin-Obukhov length play in determining the flow characteristics in both stable and unstable atmospheric conditions?
  • The Monin-Obukhov length scale serves as a critical parameter in distinguishing between stable and unstable atmospheric conditions. It indicates how buoyancy forces compare to mechanical turbulence; shorter lengths suggest a dominance of buoyancy (unstable), while longer lengths indicate that wind shear (stable) has greater influence. This length helps in predicting how temperature and wind profiles vary in different stability regimes, thus guiding atmospheric modeling and analysis.
• Evaluate how Monin-Obukhov similarity theory enhances our ability to model pollutant dispersion in urban environments.
  • Monin-Obukhov similarity theory significantly enhances pollutant dispersion modeling by providing a framework for understanding how local surface characteristics affect turbulent mixing. By incorporating stability conditions through the Monin-Obukhov length scale, models can more accurately predict how pollutants are distributed in urban areas. This knowledge allows for better air quality assessments and regulatory measures as it accounts for factors like building density, surface heat fluxes, and prevailing winds that influence pollutant behavior in complex urban atmospheres.

Related terms

Turbulence: The chaotic, irregular motion of air that affects flow characteristics in the atmosphere, particularly in the boundary layer.

Stability:

A measure of how the atmosphere resists vertical motion; it can be stable or unstable depending on temperature gradients and heat flux.

Surface Layer: The part of the atmospheric boundary layer that is directly influenced by surface characteristics and turbulence, typically extending from the surface up to about 10% of the boundary layer height.