Cloud Streets and Langmuir Streaks

#2573 "Halloween Sunset on Fire" 11x14 oils

In Making Chili Science, we used hand waving to describe how long lines of cloud form in the atmospheric planetary boundary level, the PBL. The cloud streets only required some wind, a boundary and a slight amount of instability perpendicular to the boundary. By the way, the Chili was delicious and heated on the wood stove! 

Chili Science Graphic using Empty Bean Cans

Similar lines occur on a lake and they appear in many of my paintings including "Halloween Sunset on Fire". The surface of the water is the boundary and it is easy to surmise that there can easily be some vertical motion of the water in the lake boundary layer.  The lake boundary layer is called the mixed layer depth or the MLD in physical oceanography. Those lines in the lake form within 30 minutes of the wind shift. 

The comparison of the oceanic mixed layer depth (MLD) to the atmospheric planetary boundary level (PBL) is identical. When the stresses at the surface are large (wind, solar heating, friction) and the stratification is small, the fluid becomes well mixed. The properties of the fluid such as velocity, temperature, salinity and pollutants are nearly uniform in the vertical within the depth of mixed layer - whether the fluid be air or water. 

The science in both the atmosphere and the ocean are essentially the same. The available explanatory graphics are typically much better in the oceanographic literature but we are working to change that starting with the Chili cans. 

Irving Langmuir (1881-1957)

It is important to be naturally curious and Irving Langmuir (1881-1957) was such a man. Langmuir was an American chemist and physicist who won the 1932 Nobel Prize in Chemistry for his work in surface chemistry. While observing windrows of seaweed in the Sargasso Sea in 1927, Irving developed his own brand of hand waving chili and he gave those streaks his name. In my painting above, I associate the calm and bright, mirrored bands as lines of downwelling. The rippled bands are upwelling in the Langmuir Streak Conceptual Model. Think of the ripples as a shattered mirror in thousands of pieces primarily reflecting the larger area of dark sky overhead. The flat areas of calm water is a great mirror angled to best reflect the sunset on the horizon.  

The similarities between Langmuir Streaks and Cloud Streets are clearly not coincidental. Provide a boundary for a fluid, a dash of instability and stir briskly with wind … and nature will cook up a line within that well-mixed layer. The accompanying atmospheric example of turbulent stratocumulus cloud streets is based on a photo I took - artistic licence is not a factor in the photo. 

This picture reveals all of the important facts. The wind direction is revealed by the gravity waves on the lake. The long lines of backlit cumuliform cloud are parallel to those winds. The process that created those lines are the same as described by our friend Irving Langmuir back in 1927 before the Great Depression. 

#2468 "COVID Contrail Singleton Sunset"

Langmuir Streak circulations also shape snowsqualls but we can look even further afield. Long lines of cirrus cloud can also be see at the top of the troposphere! It was not a big step for me to also call those icy bands of cirrus, Langmuir Streaks. The tropopause is the stable layer at the top of the portion of the atmosphere which contains much of our weather. The "trop" is a very effective boundary in the atmospheric fluid. The jet stream provides the wind that mixes everything together in the layer beneath the tropopause. The relative jet speed maximum provides the vertical instability. Presto, lines of cirrus appear in what was previously just called a single mass of baroclinic zone cirrus. 

The dominant line on the left in the accompanying painting is a jet contrail but the rest of the banding in the cirrus is the result of Langmuir Streaks. The gravity waves within the bands reveal the wind direction. I also used this painting to describe the drifting contrail. That contrail post contains the original photographic inspiration that is free of any artistic licence . 

Art and science are the same thing and both are inspired by observing the nature of things - being naturally curious. Just my opinion of course. None of this stuff is going to be on any pop quiz anytime soon. 

Warmest regards and keep your paddle in the water,

Phil the Forecaster Chadwick