Surface Wind Direction Variability

Common large shifts of wind direction in the weak-wind nocturnal boundary layer are poorly understood and are not adequately captured by numerical models and statistical parameterizations. The current study examines 15 datasets representing a variety of surface conditions to study the behavior of wind direction variability. In contrast to previous studies, the current investigation directly examines wind direction changes with emphasis on weak winds and wind direction changes over smaller time periods of minutes to tens of minutes, including large wind direction shifts. A formulation of the wind direction changes is offered that provides more realistic behavior for very weak winds and for complex terrain.