The sound of the sun

I mentioned in an earlier post that sitting at the beach gives us a chance to listen to the voice of the sun. While this may sound like a 60s flashback — and fifty-plus years on I must confess that it’s getting increasing difficult to tell the difference — I promise that there is actual science to back up the claim.

I also made the cavalier statement that the overall sun-to-wave-to-beach equation was simple, and it is. But… that doesn’t mean that the process wouldn’t benefit from a bit of clarification in uncomplicated words that we can all understand.

So, let’s take this puzzle one easy step at a time, and try to get from our favorite fusion reactor in the sky to the shore…

Earth has two sources of energy: the internal geothermal heat that powers plate tectonics and the rock cycle, and the external solar energy the fuels the surface processes, including such favorites as weathering and erosion, stream flow and glaciers, groundwater, weather and climate… and waves in the ocean.

There is continuing uncertainty about how electromagnetic energy from the sun travels through space, with the main contenders being: sine waves (this proposal is supported by the various “wavelengths” depicted for the different types of energy; such as ultraviolet, the visible spectrum, and infrared); actual particles (often called “photons” by those into quantum mechanics, and supported by the fact that — although they apparently have no charge or mass but are spinning — they can be trapped and stored in solar energy collectors); or some other way that has yet to be determined.

But no matter how the energy is transmitted — and I’m absolutely certain that someone a whole lot smarter than me could explain this part ever so much better — it travels through the near-vacuum of space until it hits the earth. (Feel free to excoriate me in the comment section all you want…)

It may be important at this juncture to remember that the earth is greater than 70% water at the surface.

Some of the solar energy is reflected back into space (the efficiency of the reflective surface is defined by a variable called albedo, which has a really fun formula that we absolutely do NOT want to consider at this time). Any reflective surface can increase the earth’s albedo, such as clouds or glacial ice or whatever else may get in the way — go snowboarding on a bright, sunny day and you’ll learn all you need to know about albedo. This reflected energy is lost, and we can essentially ignore it for the remainder of this discussion. So sad, but so it goes…

The rest of the energy is absorbed by whatever it hits, and — as stated above — since approximately 70% of the surface is covered by the oceans, most of this ends up in the water, having been converted to heat energy.

(Another important, and alarming digression: this is one of the reasons that climate change is such a problem, and will continue to be for a very long time… no matter what we do in the short term. You can thank the “high heat index” of water for this, but we’ll circle back to that in a later post. For now, suffice it to say that the ocean has been slowly getting hotter, and will only cool back down just as slowly.)

Anyway, it stands to reason that more energy is absorbed in some parts of the earth than in others — to restate the earlier post, consider the difference between how much solar energy is soaked up at the equator (which is mostly water), and the poles (which are mostly covered by reflective ice).

The obvious result is that there is a wide variation in the amount of ultraviolet energy radiated from the sun that is stored as heat energy in the ocean.

So here we are with massive amounts of solar energy converted to heat and stored in the sea. But, as stated in an earlier post, energy is happiest when it’s moving from place to place, so the heat doesn’t all stay in the water — much of it as re-radiated back into the atmosphere.

And guess what: the air above warmer parts of the ocean gets more heat than the atmosphere above cooler parts of the ocean. (B.T.W.: The same energy conversions also take place on the 30% of the earth that is covered with land, and — best of all — the same parameters and constraints hold so we don’t have to juggle a different set of variables.)

So now the energy that started at the sun has been radiated through space, stored in the ocean, and then cycled into the atmosphere. “Then what happens” I hear you cry…

Well, the variations in energy directly affect the local density and pressure of the atmosphere (they also affect the seawater as well, leading to what are aptly called “thermohaline currents,” but that’s for a later discussion).

Anything to do with the climate is complex well beyond the understanding of anyone without a supercomputer (and even they usually struggle to get it right). But in simple terms, warmer air has a lower density and pressure than cooler air and wants to rise.

So it rises (most of the time — this may try to adhere to the predictability of physics, but all science is bounded by the uncertainties of geology, and most especially the 1st Law of GeoFantasy).

But one thing is not uncertain: the rising airmass leaves a hole in the atmosphere. This void never lasts for long, and is immediately filled by cooler air blowing in from the side. This sets up global wind patterns (details planned for a later post), with the winds blowing across the surface of the ocean from areas of higher pressure to areas of lower.

So now our solar radiation — having cycled back and forth between the sky and the ocean and the atmosphere — has been converted to kinetic energy barreling across the surface of the sea.

You just gotta love friction. Not only does it keep our tires on the road — as opposed to in the ditch — it also transfers the energy back into the water, leads to the formation of swells, and eventually sine waveforms (again). The good news is that now they are in the water where we can finally see them!

Waves travel until they run into something, and as we already know, they don’t lose any of their energy while in deep water. So… a twenty-footer in the North Pacific is still a twenty-footer when it attacks the beach here in Oregon.

When it finally gets to the beach, the energy is changed once again, this time into mechanical and acoustical forms. Both are easy to understand, and obvious: the mechanical form of the sun’s energy eats the coastline and moves the sand around, while the acoustical waveforms make the sounds that we hear.

And here we are — we made it!

So the next time you sit on the beach and search for the center while listening to the waves moving sand around, realize that the sounds you are hearing are actually the voice of the sun: telling you once again that you are not alone… and that it is one hell of a lot more powerful than any of us will ever be.