4.3.2: Wave environments
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J. L. Davies and Clayton (1980) identified four major deep water wave environments (Fig. 4.9):
- Storm wave environments;
- West coast swell environments;
- East coast swell environments;
- Protected sea environments.
Besides, he identifies trade and monsoon influences and tropical cyclone influences.
The global wave environments are strongly linked to the zonal wind systems (Sect. 4.2) and have the following characteristics (see also Short, 2005):
Storm wave climate
- The most important and energetic wave environment;
- Locally generated by westerlies and associated mid-latitude cyclones;
- Located between 40° and 60° N and S;
- Operates year round in the Southern Hemisphere and in winter in the Northern Hemisphere;
- Generally a combination of sea and swell is present at a certain location.
- Waves are steep, short-crested, irregular and multi-directional (sea);
- Direction is predominantly westerly (to southwesterly in the Northern Hemisphere) impacting west facing and south facing (NH) coasts;
- Deep water wave heights are 2m to 3m 90% of the time, 5m to 6m 10% of the time;
- Wave periods are about 5 s, longer during storms
West coast swell climate
- Stems from storm waves generated by westerlies in the Northern and Southern storm wave belt (highest and most persistent is the westerly swell generated at 55°S). Note that swell in the Northern Hemisphere can be generated in the Southern storm wave belt and vice versa;
- Located between 0° to 40° N and S;
- Year-round in the Southern Hemisphere, seasonal (in winter) in the Northern Hemisphere (like the storm waves from which they originate);
- West coast swell reaches west coast of Americas, Africa, Australia and New Zealand;
- Swell tends to arrive more from northwest when generated in the Northern storm wave belt and from southwest when generated in the Southern Hemisphere;
- Consists of persistent and long period waves (typical period of 10 s);
- Waves are uniform in direction, shape and size and wave heights are moderate to high (typical wave heights are for instance 1 m to 2 m off swell dominated coasts);
- There is not much variation in wave heights around the mean (only by the effect of tropical storms occurring for instance once a month for Queensland, Australia);
- In the tropics (for instance Angola, see Fig. 3.12) swell can also stem from trade winds.
East coast swell climate
The east coast swell climate has many of the characteristics of west coast swell. They originate from storms in the same storm wave belts as the west coast swell but are directed such that they reach east-facing coasts. They are generally lower than west coast swell and arrive less frequently than west coast swell.
Protected wave environments
Protected wave environments are areas protected from the arrival of swell and with irregular, low-amplitude waves from local winds. It concerns areas shielded by ice (in the polar zones), reefs (in the tropics), island archipelagos or land masses. An example of the latter are enclosed or semi-enclosed seas such as the Mediterranean.