Catch A Wave

Here we go again

Another round-trip for all of my friends

Another non-stop

Will it ever end

- L. Tomlinson/L. Payne/One Direction Clouds

Little H surfing at Makorori Beach, Dec 2016

In one of my many lives before medicine, I was an oceanographer. I started out chasing a Marine Biology degree in Hawaii and graduated from Boston University with a degree in Biology with Marine Science Specialization. I then went on to graduate studies in Oceanography at Texas A&M Univ. From there, I went to work for an oil exploration company, mapping the sea floor looking for likely undersea oil and gas drilling sites. I love what I do as an Emergency Medicine doctor, and clearly made the right choice in my career change; however I totally dig geology, Earth sciences, physics, and marine science. Please indulge me while I geek out a little for this post.

One of the most soothing and calming experiences many people can describe is sitting and watching ocean waves roll in and crash on the beach. The sound of crashing waves is a common component of white noise sleep machines, and "music" in spas and during meditation exercises. The essentially flat ocean surface, endless horizon, and metronomic motion are calming. While neuroscientists struggle to understand and describe the effect of ocean waves on our brains, physicists have had much more success studying how waves form and what influences their shape.

Foxton Beach, May 2017

Waves appear to push the water forward, endlessly crashing on the beach. In reality, the wave travels through the water while the water itself just moves up and down (it's actually a little more complicated that that ... the water moves in small circles with no net gain in position). As the wave moves toward shore, the shallower water decreases the wave speed so wave length becomes shorter and the peak height increases. The wave peak moves faster than the water below, becomes unstable, and breaks forward. Air is trapped in the breaking wave crest and generates the distinctive and familiar sound.

While this describes how waves move and break due to velocity shear in a single liquid, like waves crashing at the beach, it does not describe how they break in deep water. For that, we have to turn to the efforts of Lord Kelvin and Hermann von Helmholtz. William Thomson Lord Kelvin (1824-1907) was a mathematical physicist at the University of Glasgow. His work was important to the formulation of the first and second laws of thermodynamics. Absolute Temperature i.e. Degrees Kelvin, is named in his honour. Hermann von Helmholtz (1821-1894) was a German scientist who made important contributions to our understanding of energy, electrodynamics, and thermodynamics. He is popularly known, however, for his work in describing how the human eye works. He was the inventor of the ophthalmoscopic, a tool hanging on the wall of almost every doctor's exam room, and one I use multiple times a day in my role as an ED physician.

Kelvin-Helmholtz clouds are thought to be the inspiration for the sky in van Gogh's Starry Night

The Kelvin-Helmholtz Instability describes how waves form when there is a velocity difference across the interface between two fluids. The most common example would be the formation of waves as wind blows over water. Kelvin-Helmholtz clouds form when there are two different atmospheric layers moving at different speeds. They form on windy days when there is a difference in air densities between layers. The faster upper layers "scoop" the top of the cloud into waves.

Kelvin-Helmholtz clouds over Palmy, June 2017

Walking into the hospital one day, Kari and I saw these clouds against the mountains and I was lucky enough to get a photo with my phone. To form, they require moist (yeah, I said it) stable air without upward movement and a steady wind source. They are generally very rare and transient. Interestingly, they have been seen and photographed by others in Palmy on at least two other occasions this year, in February and again in May. I have written previously about how persistently windy it is here in Palmy (Link: Up Hill, Both Ways!). I wonder if there is something about the local weather pattern that predisposes to this phenomenon, or if we just got lucky.

Science is fun ...