SUP Surfing 101 Theory Track Chapter 15

No, you didn’t miss anything, This ebook is being written in four parallel paths: Basics; Surfing; Theory, and Conditioning.  It will also eventually have a lot of pictures and video added. I have an outline, a shot list, and plans for the videos, but they have to wait until I can get to them. I’ll add them later and then integrate the whole into a complete book. So that’s the plan, and with Chapter 15 we begin the wave theory track. This track will help you learn to predict waves at your local and distant breaks. It starts with general wave theory–how waves are formed, how they travel, how they become surf-able (or not) and as much science as I can stuff in without equations. Subsequent chapters cover swell angle and refraction into breaks, tidal effects, wave buoys and maps, using different wave forecasting sites effectively and how to build a wave forecast.

I think you’ll find this useful, perhaps the most useful section in the book for surfers. I used a lot of source material for this section, some of it really impenetrable. The most useful theory book for surfers, hands down, is Surf Science: An Introduction to Waves For Surfing by Tony Butt and Paul Russell. If you are a serious surfer, then surf immediately over to Amazon and grab a copy. Simply excellent: Surf Science: An Introduction To Waves For Surfing

A little less technical, but more oriented towards forecasting is the Wet Sand Wavecast Guide To Surf Forecasting by Nathan Todd Cool. If all you want to do is learn to use forecasting tools then this is your book: The WetSand WaveCast® Guide to Surf Forecasting: A Simple Approach to Planning the Perfect Sessions.

Let’s dive in:

What We Surf On

Waves are oxygen to a surfer–not something you can go without for long. When we don’t have them we want to know when they will be back. Even the most unquestioning grommet has sat in the lineup and wondered why the good waves come in threes, of fives, or whatever. And then there’s that guy with no neck, huge deltoids and the hundred yard stare that says things like “the tide is going out and the swell’s at 14 seconds out of the north northeast, so we should be seeing some good faces in less than an hour”.

What? How does he know that, and what does it mean. And wouldn’t that be a good thing to know? Perhaps we could distill all the theory down to just the very basic stuff you need to know to be somewhat predictive. But you will never really understand waves unless you understand the fundamental mechanics of what they are, how they are formed, how they travel, why they peak up and break, and why wave forecasting is so hard. So we’re going to tell you about that.

In the beginning…

Waves are solar energy, converted to another form. Of course all energy on earth comes from our sun, except nuclear energy which comes from the heart of a star that exploded as a supernova a few billion years ago–but that’s a different story. The sun’s energy reaches the earth in the form of light, is adsorbed in the atmosphere, water and land and converted to heat. It’s not an even heating process–the poles don’t get as much heat as the equator, and one pole is warmer than the other depending on the tilt of the earth as it travels around the sun (winter and summer), and water and air convert less light to heat than dirt, trees, grass or rocks do.

This differential heating is the source of waves. Well, that and the Coriolis effect–the gentle force associated with the earths rotation that makes cyclones spin in the opposite direction from hurricanes. And local highs and lows, and refraction from the sea bottom, sediment shifting, currents, storms a few thousand miles away and a butterfly flapping it’s wings in Malaysia. In other words, it’s a bit chaotic and complicated. But the basic source is uneven heating of the air making wind.

On a local basis, especially in the islands, the effect of warm air over the land and cold air over the water is pretty clear. In the mornings, the ground warms up and heats the air above it, the warm air rises, and the cooler, heavier air over the ocean rushes in to fill the void. The result is convection winds. Get up early enough in the morning and you’ll find less wind, since the machine takes a while to get going. You can even see it sometimes on a micro basis–a hawk in a circling climb over a black parking lot, taking a free ride on the thermal.

On a global basis, the poles have colder air than the equator, so there is a continual exchange of cold polar air pushing down into the tropics. Air rises at the equator and sinks over the poles, so there’s a continuous circular exchange.

Now we add in the Coriolis effect, generated by the earth’s spin. The Coriolis effect is the reason why every large scale motion in the Northern Hemisphere turns to the right and everything in the Southern Hemisphere swerves left.  It’s generated by the relative speed of the earth at different latitudes. On the pole, you have no ground speed at all–you just spin. At the equator you’re zooming along at 994 MPH. If you send a powered blimp from the pole to the equator in the Northern Hemisphere it would steadily lag behind relative to the earth’s surface unless it stops long enough for the air to accelerate it to something close to groundspeed. While it’s moving south, it’s swerving right each bit of ground is traveling a little faster. Turn it around and send it north and it’s still swerving right as each bit of ground it travels over is moving a little slower. If you push your blimp east your push will give it a higher speed than the rotational speed, which increases the moment of inertia (we can call it the Centrifugal force, even though there really is no such thing). This results in a swerve to the right towards the band of earth with the same grounspeed. You mighthave an easier time visualizing this as a particle stuck lightly to a spinning ball. Drag a little bit on the particle to slow it and it will move towards the pole where the rotational speed is slower. Push on it to make it faser and it will spin outwards towards the equator of the ball to match it’s new speed.

The net result for a north south north voyage is a circle. Weird, eh, but you can look at the effect anytime by watching a weather forcast and seeing those big circling lows that are visible because they condense warm wet air into clouds and fog.

Even something as relatively compact as a tornado is commanded by the Coriolis effect to spin right in the North, and left in the Southern Hemisphere. Not so sure about the toilet bowls and sink drains.

With the Coriolis effect added, the transfer of air between the warm equator and the colder pole is now a lot more complicated. You might think at first that it would change into a spiral, but remember the net motion tends to be always towards the right in the north, left in the south. So instead of a south-north spiral we get cells of air moving in big circles. In fact the way things work out there are six rotating bands from North to South Pole, spiraling steadily in opposite directions north and south of the equator, creating a complex series of high alow pressure areas. Add to this the fact that the forces are more intense when a pole is in winter (a bigger temperature difference between equator and pole) and the huge effects that continental masses have, and we have a very complex system of wind and pressures.

We’ll talk about how that generates waves and makes them propagate in the next chapter.

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