May 22, 2022

EBB AND FLOW

Once I was asked what time I was free on Thursday, I replied: “I should look at the tide chart.” Of course, the ebb and flow dictate the surfer’s schedule. But what they depend on, I will analyze in detail

What are the ebb and flow?

The ocean is in constant motion, expressed by the waves breaking on the shore and the continuous change in the water level

If you spend the whole day on the beach, you will notice that the beach becomes sometimes narrower, sometimes more comprehensive, and the waves, which were noisy about 5 meters an hour ago, suddenly roll right onto your feet, threatening to wash off your flip flops and sun loungers.

So the water level is constantly changing. When the water rises, it is a high tide; when it decreases, it is low tide.

I believe that the terms maximum and minimum water do not need explanation. The waves depend on the sun, moon, and the Earth’s daily rotation.

The sun and the moon attract the Earth’s water due to gravitational forces. If you forget, gravity is proportional to mass and inversely proportional to the square of the distance.

The sun is significant and far away; in general, its gravity acts on the entire planet, forcing it to rotate in its orbit, but since water is more plastic, it is somewhat pulled towards the star.

Although much smaller than the sun, the moon is closer, so the gravitational interaction is palpable.

If you are interested in exact numbers, then the gravitational force of the Sun is Fc = 3.6 × 1022 N, and the gravitational pull of the Moon is Fl = 2 × 1020 N

In theory, the water should be drawn into a “droplet” with a noticeable bump directed towards the resulting force, which is calculated according to the vector addition rule.

However, there is also a second tubercle on the opposite side, and its formation mechanism is a little trickier.

We used to say that the moon revolves around the Earth, although both of these objects are massive and revolve around their common center of mass.

It’s just inside the Earth, about 2/3 of the radius from the center to the surface.

It can be noticed just by the second hillock of water on the opposite side of the Earth from the moon; it is pulled out by inertia, which in this case, for understanding, can be called centrifugal force.

If you look from space, then in 24 hours, the Earth makes a complete revolution, and each point of the planet passes under both hillocks; here they are – two tides a day

From the point of view of a person standing on the ground, the tide can be imagined as a vast ring of water that encircles the Earth and makes a complete revolution around it in a day.

Why do the tides differ in height?

Now let’s take a closer look at the water level graph for the month.

It is seen that the maximum and minimum water are either very different or vice versa, slightly fluctuating around the average level. It is due to the change in the phase of the moon.

On a new moon and a full moon, the moon and the Sun line up, and the force of their attraction is added.

During periods when the Earth-Moon and Earth-Sun axes are perpendiculars, on the contrary, they pull in different directions, averaging the change in water level.

Everything would be fine, but the described picture is very idealized – it would be precisely the same if the whole Earth were covered with an even layer of water

Islands, continents, and even the seabed depth have a strong influence on the trajectory of water movement.

As a result, it turns out that in some places, the ebb and flow are almost the same in height, while in others, on the contrary, the difference turns out to be staggering.

So, when the tidal hillock meets the continent’s vast coastline on its way, the water has nowhere to go forward, and the “back rows” are already pushing. As a result, the tide intensifies.

The world record holder for waves is the Bay of Fundy, Canada, where a water level drop of 16.3 meters is recorded

In some regions of Great Britain, between England and Wales, there are also regular tides up to 15 meters high.

But small islands lost in the ocean, this wave passes without notice, where the water level changes slightly during the day, literally by 1-2 meters.

But, for example, in the strait off the coast of Alaska and in the Gulf of Mexico, there is only one high tide and one low tide per day; this is not an anomaly, just a combination of the structure of the bottom, coastline, and currents.

What does surfing have to do with it?

Why do surfers care about the ebb and flow?

Because where the difference in water level is significant, it affects wave quality and spot performance.

At low tide, when there is little water, the bottom is close, the wave rises sharper and can close along its entire length.

On the contrary, there is too much water at high tide, and the lock can be “oily”; it is difficult to get over it. In general, the relationship between the spot operation and the water level is individual and depends on the specific bottom configuration.

So, when choosing a spot for surfing, you also need to find out what kind of water it works on and what time this water is on schedule, which already makes up the rest of the daily routine.

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