Applicability of the generalized wind profile model over mountainous forests

Area of Science:

• Atmospheric Science
• Environmental Science
• Geophysics

Background:

• The Monin-Obukhov (M-O) similarity theory provides a wind profile equation widely used for predicting wind speed over flat terrains.
• Its applicability and accuracy over complex terrains, crucial for estimating aerodynamic parameters like zero-displacement height (d) and roughness length (z), remain largely unvalidated.
• Accurate aerodynamic parameter estimation is vital for flux calculations (carbon, water, trace gases) using methods like vorticity covariance.

Purpose of the Study:

• To evaluate the applicability of a generalized wind profile model based on M-O similarity theory in complex mountainous terrain.
• To compare the model's performance in complex terrain with its performance in a flat agricultural landscape.
• To determine the primary factors affecting the wind profile model's accuracy in different terrains and seasons.

Main Methods:

• Three-dimensional wind speed data were collected using three flux towers in a watershed at Qingyuan Forest CERN (complex terrain).
• Data from the complex terrain site were compared with data from Panjin Agricultural Station (flat terrain).
• Statistical analyses, including coefficient of determination (R²), standard error, and F-test, were used to assess model performance.

Main Results:

• The M-O based wind profile model significantly underestimated wind speeds in complex terrain, with R² values between 0.12 and 0.30.
• Predicted wind speeds in complex terrain were substantially overestimated, sometimes by a factor of two, with a standard error up to 2 m·s⁻¹.
• In contrast, the model accurately predicted wind speeds in the flat agricultural landscape (R²: 0.90–0.93, standard error: 0.5 m·s⁻¹).

Conclusions:

• The generalized wind profile model is not suitable for predicting wind speeds in complex terrains, particularly over forest canopies.
• Underestimation of zero-displacement height (d) and roughness length (z) in complex terrain leads to inaccurate aerodynamic height estimations.
• Terrain complexity is the primary factor limiting the model's applicability, with seasonality (leaf-on/leaf-off) as a secondary influence.