The Swell Life: Mechanics of Wave Production

2017-11-22 00:46:16


Oh, swell. As surfers, it’s one of our favorite words in the English language. Whenever there’s a swell event on the horizon, we tend to ask ourselves the same questions that news reporters tend to ask when hunting a story. Who are we surfing with during the swell? What will we ride? When will it arrive and when should we surf? Where will the swell fill in the best? Why haven’t we come up with a reason for skipping work yet? And how are we going to accomplish all this before the swell arrives?

swell


Photo: Eddie Sahmi It’s a wild ride, to say the least. And one that never gets old. But before we move further down the path of accomplishing these feats, shouldn’t we clarify what caused the swell in the first place? Many beginners don’t quite understand how waves are formed, which happens to be treasured knowledge down the road when figuring out where and when to surf. So, let’s take a look at the three primary variables that play into wave production. I’ll give you a hint, they all have to do with the wind.

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Wind Speed

This one is fairly obvious. The faster the wind blows, the bigger the waves. To understand this more fully, wind forms from pressure gradients across the globe. The greater the pressure gradient that is between high and low pressure, the higher the wind speed between them. There are also diurnal wind patterns in more tropical zones where breezes develop due to temperature differences, but these are usually light and don’t contribute to actual wave production. Just quality.

Wind Duration

Take all that wind speed and allow it to last for a certain period of time. That’s when wind swell really starts to pick up in intensity. It then stands to reason that the longer a wind event occurs over the ocean at consistent, sustained speeds, the larger the swell and the stronger the energy. However, this means nothing if the area isn’t large, or the wind is blowing in the wrong direction.

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Good Swell Demands Large Wind Fetch

Wind fetch, the most important out of the three, is defined as the duration over which consistent winds blow across the open ocean. For example, if wind speeds of 30-40kts blow over the distance of 100 miles, wave action will be limited, localized, and small. However, If those same winds blow over say 800-1000 miles, well then you have a collection of surfers asking themselves the aforementioned series of questions. Fetch is everything, though it needs to be pointed in the direction of your local beach in order for you to reap the rewards of the storm. As we move forward, we’ll cover what happens when these waves reach the shore and how your local coastline interacts with this incoming energy.