Small-scale motions and variations of microclimate on horizontal scales less than a few kilometers are understood only in very idealized cases. This website provides some insight into more realistic complex variations with the concession that full understanding is not possible. This perspective is obtained by combining basic understanding with visual evidence based partly on natural and machine generated fog. Such visualization reveals true spatial structure of the motions that can be only tentatively inferred from the usual fixed point measurements.
While the website is designed for individuals with at least some nominal background in the atmospheric sciences or fluid dynamics, some practical reports embedded further within the website are designed for readers with little background.
Small-scale motions are roughly classified as turbulence, submeso motions, or mesoscale motions. Turbulent motions occur on the smallest scales. These three-dimensional turbulent eddies transport heat, moisture, momentum and other quantities between the ground surface and the atmosphere. Submeso motions include a rich variety of motions generally on horizontal scales larger than the turbulence but smaller than a few kilometers. Scales larger than a few kilometers are normally referred to as mesoscale motions.
Submeso motions are particularly important with stable conditions (clear nocturnal skies and weak winds) but are often important in the daytime as well. Transient submeso motions include wave-like modes, microfronts and a broad variety of other structures found under the submeso menu on this site. The second class of submeso motions are those attached to surface features and include downslope cold air drainage at night and daytime upslope flow of warm air in the daytime. The discussion of this class of motions can be found following the Local Circulations menu.
Mesoscale motions include sea-breezes, thunderstorms, and local circulations associated with larger valley-mountain systems. Currently, mesoscale motions are outside the scope of this website. All of the aforementioned types of motions can interact. As with any classification of atmospheric motions, the current classification serves only as a framework to organize our thinking. Some types of motions have features of more than one class.
The Micrometeorology menu includes a variety of topics associated with horizontal variations of surface conditions such as vegetation, soil conditions and water bodies, mostly on a horizontal scale of about one kilometer or less. Micrometeorology is a traditional field that overlaps with the “local circulations” topic but often focuses more on how local surface energy budgets relate to vegetation and soil conditions.
“ARFM Videos” contains three videos based primarily on time lapse of natural and machine-generated fog that was created for Annual Reviews of Fluid Mechanics (46, 23-45).
This website is an adventure of perspective on the complex real world partly through visualization, not obtainable with traditional instrumentation. This project is supported by the National Science Foundation through Grant AGS-1614345.