3.5 Wind-Generated Waves
99
3.5.4 Geography of Waves
Wind and wave climate varies considerably between various regions of the
World Ocean. Peak wave conditions occur at high latitudes (±500). In the
Southern Ocean, the almost constant strong winds acting over large fetches
generate consistently high waves, which propagate over very long distances. In
contrast, the North Atlantic Ocean has a more variable sea state. In all oceans,
the intensity of wave motion decreases from high latitudes towards the Equator. In the tropical zones, the frequency of storm winds is 2-3 times smaller
than in higher latitudes. However, the tropical regions are the locations where
cyclones (or hurricanes or typhoons) are generated. Due to the complicated
pattern of the wind field, the resulting storm waves are usually superimposed
upon swell propagating from various directions. Some parameters of extreme
wind speed and wave heights, occurring once in 30 or 50 years (TR = 30 or 50
years), in various regions of the World Ocean, are given in Table 3.2, based on
data reported by Davidan et al. (1985). However, the wind speed during tropical cyclones was omitted from the table. Confidence intervals with confidence
level of 95% are added in parentheses.
The Atlantic Ocean extends from north to south through all climatic zones.
The number of atmospheric depressions in the Atlantic Ocean is higher during
winter (October-March) and decreases during summer (Massel, 1982). During
tropical cyclones the wind speed exceeds 40 mis, reaching 70 mls and more,
and waves can be as high as 20 m. During tropical cyclone Camille (1969) in
the Gulf of Mexico, a wave height of 23.6 m was recorded. The S.S. Majestic's
officers observed waves from 18.3 m to 27.4 m near 48°30' Nand 21°05'W on
December 29, 1922. The passenger ship Michelangelo, during a North Atlantic
crossing, was struck by a wave that collapsed the superstructure and broke
heavy windows at 24.6 m above the water line (Massel, 1996a).
The Pacific Ocean is the largest ocean with the greatest average, as well as
the greatest observed, depth. Especially in the Southern Pacific, the large,
almost unlimited wind fetches create conditions for generation of large waves.
For example, on April 2, 1966, the S.S. Ob's officers measured a wave of 24.9 m
using the stereophotogrametry method. In 1921 Captain Wilson of the Blue
Funnel Line, while en route from Yokohama to Puget Sound, Washington,
recorded waves that were higher than 21.3 m. The U.S.S. Ramapo, a navy
tanker, encountered a wave of 33.5 m on February 7, 1933, between Manila
and San Diego.
There are two distinct regions of the Indian Ocean, characterized by different
climates. The northern part is dominated by the Asian summer monsoon, while
in the southern part, between 40 0 S and the Antarctic continent, the powerful
Westerlies are located. The swell generated in the Southern Ocean propagates
towards lower latitudes, resulting in a more energetic wave climate in the Indian
Ocean. The waves are consistently larger than those in either the South Pacific
or South Atlantic Oceans.
99
3.5.4 Geography of Waves
Wind and wave climate varies considerably between various regions of the
World Ocean. Peak wave conditions occur at high latitudes (±500). In the
Southern Ocean, the almost constant strong winds acting over large fetches
generate consistently high waves, which propagate over very long distances. In
contrast, the North Atlantic Ocean has a more variable sea state. In all oceans,
the intensity of wave motion decreases from high latitudes towards the Equator. In the tropical zones, the frequency of storm winds is 2-3 times smaller
than in higher latitudes. However, the tropical regions are the locations where
cyclones (or hurricanes or typhoons) are generated. Due to the complicated
pattern of the wind field, the resulting storm waves are usually superimposed
upon swell propagating from various directions. Some parameters of extreme
wind speed and wave heights, occurring once in 30 or 50 years (TR = 30 or 50
years), in various regions of the World Ocean, are given in Table 3.2, based on
data reported by Davidan et al. (1985). However, the wind speed during tropical cyclones was omitted from the table. Confidence intervals with confidence
level of 95% are added in parentheses.
The Atlantic Ocean extends from north to south through all climatic zones.
The number of atmospheric depressions in the Atlantic Ocean is higher during
winter (October-March) and decreases during summer (Massel, 1982). During
tropical cyclones the wind speed exceeds 40 mis, reaching 70 mls and more,
and waves can be as high as 20 m. During tropical cyclone Camille (1969) in
the Gulf of Mexico, a wave height of 23.6 m was recorded. The S.S. Majestic's
officers observed waves from 18.3 m to 27.4 m near 48°30' Nand 21°05'W on
December 29, 1922. The passenger ship Michelangelo, during a North Atlantic
crossing, was struck by a wave that collapsed the superstructure and broke
heavy windows at 24.6 m above the water line (Massel, 1996a).
The Pacific Ocean is the largest ocean with the greatest average, as well as
the greatest observed, depth. Especially in the Southern Pacific, the large,
almost unlimited wind fetches create conditions for generation of large waves.
For example, on April 2, 1966, the S.S. Ob's officers measured a wave of 24.9 m
using the stereophotogrametry method. In 1921 Captain Wilson of the Blue
Funnel Line, while en route from Yokohama to Puget Sound, Washington,
recorded waves that were higher than 21.3 m. The U.S.S. Ramapo, a navy
tanker, encountered a wave of 33.5 m on February 7, 1933, between Manila
and San Diego.
There are two distinct regions of the Indian Ocean, characterized by different
climates. The northern part is dominated by the Asian summer monsoon, while
in the southern part, between 40 0 S and the Antarctic continent, the powerful
Westerlies are located. The swell generated in the Southern Ocean propagates
towards lower latitudes, resulting in a more energetic wave climate in the Indian
Ocean. The waves are consistently larger than those in either the South Pacific
or South Atlantic Oceans.