windturning

Windturning, or turning with height, is the change in wind direction as altitude increases. It is a form of vertical wind shear and is usually described by a turning angle, the difference between wind directions at two different levels. Windturning can occur on many scales, from near the surface to the upper troposphere, and it is a common feature in mid-latitude weather systems.

Causes of windturning include the reduction of surface friction with height, which allows the wind to align more closely with the horizontal pressure gradient and the Coriolis force. Near the surface, friction slows and deflects winds, while higher levels experience less friction and more geostrophic influence. As a result, wind direction often changes with height. In the Northern Hemisphere, winds commonly veer (rotate clockwise) with height, while in the Southern Hemisphere the turning is typically in the opposite sense. Local effects from terrain, land-sea contrasts, and synoptic-scale systems can modify the pattern.

Measurement and assessment are done using radiosonde observations, aircraft wind profiles, wind profilers, and Doppler radar. Forecasters quantify windturning by comparing wind directions at two levels, such as near the surface and a few kilometers aloft, and by evaluating the overall vertical shear.

Significance lies in weather forecasting and aviation. Strong turning can influence storm organization, convection, and severe weather potential, and it affects turbulence and flight planning through vertical wind shear.