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What is the Difference Between Sea and Swell Waves?

"Sea Waves" are produced by local winds and measurements show they are composed of a chaotic mix of height and period. In general, the stronger the wind the greater the amount of energy transfer and thus larger the waves are produced. The height of sea waves depends on three factors: 1. Wind speed 2. Length of time that the wind blows over the water 3. Fetch of water over which the wind blows.

As sea waves move away from where they are generated they change in character and become swell waves.

"Swell Waves" are generated by winds and storms in another area. As the waves travel from their point of origin they organize themselves into groups (Wave trains) of similar heights and periods. These groups of waves are able to travel thousands of miles unchanged in height and period. Swell waves are uniform in appearance, have been sorted by period, and have a longer wave length and longer period than sea waves. Because these waves are generated by winds in a different location, it is possible to experience high swell waves even when the local winds are calm.

Surfers are often interested in obtaining the ocean swell height and period. Ocean swell can best be described by the wave statistics Hsig and Peak TP1^?. It is important to note that the Hsig represents an average of many wave heights recorded during a sampling period. In addition, the individual Maximum Wave Height (Hmax) recorded during the same sampling period may be up to twice the height of the calculated Hsig.

Sea and Swell waves may both be observed at the same observation station as sea waves are produced by locally occuring winds and swell waves arrive from offshore origins. To unravel the complexity of these wave "mixtures" spectral anaylsis is generally applied.

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