It all starts with the sun
Our big ball of fire does not only give us a nice tan and surfy locks, she is the source of life and the bringer of waves: wind is created when the earth is unevenly heated by the sun. This solar energy causes a difference in the atmospheric pressure. In the Southern hemisphere wind blows clockwise around a high-pressure system and reverse in a low pressure system. The same goes for the Northern Hemisphere, except the other way around. This is an effect caused by the earth’s rotation and – together with the differential heating between the poles and equator – creates different sorts of windspeed, force and duration. Gusts are those strong bursts of wind, and squalls are the ones that blow suddenly and sharp. The ones that blow longer, we can categorize by the their strength, and these are know as breezes, storms, hurricanes and typhoons.
The wind blows over the surface of the water, that friction between the wind and the water’s surface causes ripples, and those ripples eventually result in waves. The wind velocity and duration, along with the area across the ocean over which the wind blows (fetch) decides how waves are formed. The faster and the longer the wind travels across the fetch, the bigger the waves can grow, until they hit any number of obstacles like sandbanks, coastal areas, sunken boats, … More energy in the water creates bigger waves and a wider space between those waves. Therefore we notice longer seconds between the waves and sets when the swell is bigger. Local winds can also form a wave. When it is onshore we are going to get a choppy, bumpy ride. As the wind pushes in the direction of the wave, it reduces the quality of the breaking wave, making it unsteady. On the other hand, offshore wind works as a “counteract” against the wave, pushing against it and propping it up. This means cleaner waves and happier surfers.
Waves in sets
Did you know bigger waves travel faster than smaller ones? They will reach the shores sooner. This difference in division of appearance is called wave dispersion. That’s why when swell arrives first it will bring bigger waves, which are then followed by smaller ones over the next few days.
Waves carry a certain energy and as they travel away from their source it will lessen by distance. To maintain that energy they will over time group together with the ones traveling at the same speed and who are usually of the same size. It creates different wave-groups – and these different groups, we call sets.