windgradients

Wind gradients describe how the wind field changes over space, most commonly with height, but also across horizontal distances. They refer to variations in both wind speed and wind direction and are typically quantified as the gradient of the wind velocity vector with respect to position (for example, the vertical gradient ∂U/∂z or the horizontal gradients ∂U/∂x, ∂U/∂y).

Vertical wind gradients, or wind shear, are a central feature of the atmospheric boundary layer. Near the surface, friction slows the air, so wind speed often increases with height. In the upper atmosphere, terrain and weather systems can produce turning of the wind direction with height (veering) or changes in speed and direction over horizontal distance. Strong wind gradients can occur near fronts, inversions, thunderstorm outflows, jet streams, or complex terrain.

Causes of wind gradients include surface roughness and friction, atmospheric stability, temperature stratification, terrain effects, and synoptic-scale weather structures. They vary with time and location, influenced by daily cycles, weather systems, and local topography.

Impacts and significance: In aviation, wind gradients create wind-shear hazards during takeoff and landing and can cause abrupt changes in airspeed and aircraft attitude. In wind energy, vertical and horizontal gradients affect turbine performance, loading, yaw control, and wake interactions, especially at hub height and higher. In meteorology, gradients help indicate boundary-layer depth, stability, fronts, and evolving weather patterns.

Measurement and modeling: Wind gradients are estimated from towers, radiosondes, lidars, wind profilers, and SODAR, or inferred from aircraft data. They are analyzed as spatial derivatives of the wind field and incorporated into models via boundary-layer theories, Monin-Obukhov similarity, and various parameterizations of shear in numerical weather prediction and climate models.