ADDED ON MARCH 28
a) Wave-like phenomena
Wave-like motions are abundant in most of our stable boundary layers. Such modes are generally observed at fixed sites with only a few periods. Cases of more than a few periods with roughly constant period and amplitude are uncommon at the ground surface. However, such cases are emphasized in the literature and they do become more common at higher levels. Our library of several hundred fog videos and our datasets indicate that shallow wave-like motions are quite common.
b) Solitary modes
Solitary modes with a single “wavelength” are common. More work is required to establish the relationship between the wave motions and the turbulence.
Blobs of cold air seem to be common in our datasets and may arrive at fixed sites as microfronts followed by colder air. The cold air behind the microfront can be associated with particularly weak winds and weak turbulence.
Warm microfronts are sometimes associated with downward mixing of warmer air with stronger (but still weak) winds. There formation and demise is not understood. Propagating microfronts are frequently observed at some sites but not other sites. Cold microfronts are thought to be generated by accelerating cold air (e.g., density currents) perhaps originating as micro cold events but may also be initiated by horizontal convergence imposed by larger mesoscale motions.
d) Meandering Motions
Meandering motions normally refers to unpredictable constant changing of wind direction. Such changes could be associated with any of the above submeso motions but is often associated with wave-like behavior.