Mesoscale wind direction shifts in the stable boundary-layer

The observed mesoscale variability of wind direction near the surface is examined in stable boundary layers. Such direction changes are often perceived as gentle meandering of the wind direction back and forth. However, with weak winds on the order of 1 m s(-1), large sudden shifts of wind direction are found to be common, as are a wide variety of more complex variations of wind direction. This study focuses on frequent abrupt changes of wind direction. Various statistics of wind direction variation are interpreted and their dependence on scale is noted. The wind shifts are embedded within a wide variety of complex flow signatures, without emergence of a dominant type of structure. The physics of such variations remain generally unknown.