The wave is a natural phenomenon that largely determines the comfort of being on the high seas. Small waves may not even be noticed. But the big ones are capable of causing significant damage to the ship and harming its passengers. This article will focus on wind waves. What are they, how are they formed, and what characteristics do they have? Let's answer all these questions together!
Wind waves - what is it?
No body of water can remain calm and motionless. Indeed, even an insignificant in strength wind will certainly be reflected on its surface. The wind wave is formed as a result of direct impact of the wind on the water surface of the sea or lake. To better understand the mechanism of its formation, you can observe the wheat field in windy weather.
So how do wind waves form? In light winds, light ripples occur on a calm surface of the water. When its speed increases, small rhythmic waves appear. Gradually, their length and height increase. With further strengthening of the wind, “lamb” from white foam begins to form on their ridges. The speed of wind waves can vary widely (from 10 to 90 km / h). After the wind stops at sea, you can see long, low and gentle waves, called swell.
It is important to note that water is a much more dense substance than air. As a result of this, the surface of the reservoir is a little “lagging” after exposure to wind, and the ripples turn into waves only after some time.
Wind waves should be distinguished from tsunamis and tides. The former arise as a result of increased seismic activity of the earth's crust, and the latter as a result of the influence of the satellite of our planet - the Moon.
Sea wave structure
The wind wave consists of several elements (see diagram below):
- The crest is the highest point of the wave.
- The sole is the lowest point of the wave.
- Slopes - downwind and windward.
The leeward (front) slope of the wave is always steeper than the windward. Here, by the way, there is a direct analogy with sand dunes, which are also formed under the influence of wind. Approaching the shore, the bottom of the wave is braked at the bottom of the reservoir, and its crest overturns, breaking into many splashes. This process is accompanied by active destruction of rocks. If the wave stumbles upon a coastal rock, then the water is thrown up in the form of a powerful foamy column, the height of which can reach several tens of meters.
Wind wave characteristics
In oceanography, four main characteristics of the sea wave are distinguished. It:
- Height - the distance between the sole and the crest vertically.
- Length - the distance between two crests of adjacent waves.
- Speed - the distance that the crest of a wave travels per unit of time (as a rule, it is calculated in meters per second).
- Steepness - the ratio of the height of the wave to half its length.
The length of the wind waves varies widely from 0.5 to 250 meters, the height can reach 20-25 meters. The most powerful waves are observed in the southern hemisphere, in the open ocean. Here, their speed often reaches 15-20 m / s. The smallest waves are characteristic of inland seas that deeply extend into the continent (for example, the Black or Azov Seas).
State of the sea: scale
Sea state is a term used in oceanographic science to determine the state of the open surface of large bodies of water (lakes, seas, oceans). It is characterized, first of all, by the height of the waves and their strength. To assess the degree of sea disturbance, a 9-point scale developed by the World Meteorological Organization is used.
Score | Title | Wave height (m) | External signs |
0 | Perfectly calm sea | 0 | The surface of the sea is smooth |
1 | Calm sea | 0-0.1 | Ripples and minor waves |
2 | Weak excitement | 0.1-0.5 | Wave crests begin to tip over, but no foam yet |
3 | Light excitement | 0.5-1.25 | Places on the crests of waves appear "lamb" |
4 | Moderate excitement | 1.25-2.5 | “Lamb” is present in large quantities |
5 | Troubled sea | 2.5-4 | Large crests appear |
6 | Major excitement | 4-6 | Ridges form large storm shafts |
7 | Strong excitement | 6-9 | Foam stretches into strips and partially covers the slopes of the waves |
8 | Very strong excitement | 9-14 | Foam completely covers the slopes of the waves |
9 | Exceptional excitement | More than 14 | The entire surface of the waves is covered with a thick layer of foam. The air is oversaturated with water dust. Visibility drops dramatically. |
Sea waves as a source of energy
Using the natural energy of the waves of the Ocean is one of the promising areas of alternative electric power industry. Scientists have calculated that the total power of all wind waves on the planet is 10 20 J / hour. This is an enormous figure, but the trouble is that obtaining and using this energy is very difficult.
Today, countries such as the United Kingdom, Ireland, Norway and India are seriously engaged in the development of wave energy. The operation of a wave power plant is based on the conversion of the mechanical energy of the sea wave into electrical energy through working mechanisms consisting of special floats, blades and pendulums.
The first such power station was launched in Norway back in 1985. Its power is 850 kW. Today, a number of states use wave energy to power autonomous buoys, floating beacons, mariculture farms, and even small drilling platforms.