Don McLean released a guitar ballad in 1972 that flowed like a river called “Vincent,” which could be heard across the radio dial that summer as a tribute to Vincent van Gogh.
Many radio listeners, like myself, knew it as “Starry Starry Night,” the opening line of his song about his famous painting “The Starry Night.”
This beautiful painting of the night sky contains “billow, shear-gravity, fluctus or wave clouds” that mimic breaking waves on the beach. These billow cloud formations are officially known as Kelvin-Helmholtz instabilities named after two renowned 19th-century physicists Lord Kelvin and Hermann von Helmholtz.
They were early pioneers in the study of vortex dynamics, or the disturbance caused by the fluids of different speeds, directions and densities interacting with each other. You see, the atmosphere is a fluid of air made of varying air velocities and densities.
Do these Kelvin-Helmholtz instabilities form along the Central Coast? They do, but they are uncommon, and here is why.
We experience severe temperature differences in the horizontal plane from one Central Coast location to another. For example, last year on July 25, Diablo Canyon Power Plant reported a temperature of 55 degrees Fahrenheit, while just a few miles away, the PG&E Energy Education Center in Avila Valley was at 108.2 degrees. That’s a 53-degree temperature differential.
But we also see large temperature gradients in the vertical direction. This condition is called a temperature inversion — when a warmer, less dense air mass covers cooler, denser air at the surface, which we often see as the marine layer. On infrequent occasions when there is just enough wind shear (not too strong or weak) on the horizontal plane along the boundary of these two dissimilar air masses, the warmer, less dense winds scoop the heavier marine air or stratus clouds upward, but gravity pulls the crest of the cloud wave back to earth.
This condition can produce the evenly spaced rolling vortexes we call Kelvin-Helmholtz instabilities. Think of locally generated seas/waves. As the wind blows over the ocean or even a cup of coffee, the moving air along the surface of denser water can carve out small ripples in your mug to large cascading waves on the ocean, like your hand sweeping across a half-filled sink.
Higher is the atmosphere near the jet stream Kelvin-Helmholtz instabilities are more likely to develop as air masses of different temperatures, densities and velocities are more likely to interact with each other and produce cirrus (“curl of hair”), cumulus (“heap or pile”) and stratus (“layer or sheet”) clouds and the chance of awe-inspiring waves in the sky.
By the way, fluctus is the Latin word for wave, billow or disorder. Unfortunately for photographers, like the green flash, Kelvin-Helmholtz instabilities tend to be short-lived. If you’re flying and see these types of clouds, it can often indicate severe turbulence. Vincent van Gogh may have seen these clouds while in the South of France, which may have his inspiration for “The Starry Night.”
Van Gogh died about year after completing Starry Night at only 37 years of age. Over the last two years of his life, he completed over 800 oil paintings.