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at this time—summer in the southern hemisphere—the shaded area is centered along latitude 50 degrees south.
In August—winter in the southern hemisphere—the shaded band will have broadened into a swath of rough seas extending clear around the world, while in the northern hemisphere the shaded areas are gone. In other words, conditions in the Southern Ocean remain severe most of the year. Also, note the absence of large waves in the tropical zones near the equator. This area is subject to a different condition, that of tropical cyclones. These satellite observations are not programmed to detect such transient events as hurricanes. (Chapter 4 discusses wave heights generated by storms and hurricanes.)
If the world’s major oceans are sliced along a longitudinal meridian in their center, the variation of significant wave height with latitude can be examined. If this is done, HS increases from around 13 feet at 60 degrees north, to 20 feet at 50 degrees north, and then declines to 6 to 10 feet at the equator, again increasing to around 20 feet at 50 degrees south latitude. No wonder sailors call 50 degrees south “the furious fifties.”
In the Southern Ocean, the wind is generally from the west to the east, the strongest winds occurring between South Africa and Australia, weakening as you move farther west. The data also show that the significant wave height is generally higher on the west coasts of Africa, Australia, and South America than on their east coasts. One exception to the general trend is the region at 20 degrees north in the Arabian Sea. Here, strong southwest winds that arise during the summer monsoons (June to September) create waves with significant heights in excess of 16 feet.7
How do waves propagate? Surprisingly, the water in a wave produced in Hawaii does not reach California; it is the wave motion that is propagated. If you place a cork in the path of a wave, it moves forward with the crest of the wave, but then moves backward in the trough until it rises and moves forward with the next crest. So waves actually move water up and down in circular orbits. A floating object will be seen to