This 19th century painting: Älvalek, "Elf Play", (1866) by August Malmström depicts several realistic features of some submeso motions,
including changes of wind direction, small embedded eddies and thin filaments or sheets. Submeso motions are always present, but only
seen when fog or some other material provides visualization.
The common age-old expression "light and variable" refers to cases when the general wind is so weak that the wind direction is constantly changing. Have you ever sat around a campfire on a "calm" night and were unable to avoid smoke because the wind direction was constantly changing? Winds are never completely calm even though they may seem to be calm to a human observer without instruments. Background transient winds, sometimes referred to as "submeso motions", are always present and cause the wind direction to constantly change when the general wind is weak.
Submeso motions are poorly understood yet dictate the dispersion of contaminants released into the atmosphere under weak wind conditions. Yet, these are the conditions when contaminates remain in highest concentration due to minimal mixing. Computer models do not include the dominating influence of submeso motions in weak-wind conditions. What are submeso motions? This web site includes examples of different types of submeso modes, a review of existing studies and animations based on observational networks, which show the impact of submeso motions on dispersion of contaminants. Videos emphasize the complex variety of submeso motions, solitary modes and the striated structure of the very stable boundary layer.
All fog videos can be viewed on Youtube HERE.