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Sneakers on beach
80,000 sneakers and their travels across the sea have informed studies of winds and currents.
ll of Earth's major oceans have prevailing winds -- winds that blow hard and steady, in a particular, predictable direction, for at least several months of the year. Prevailing winds are crucial to the formation of waves and currents, but they can also affect climate and weather in and around the ocean basins. They can even control ocean ecosystems, through a process called upwelling that brings nutrient-rich waters up to the photic zone from tens of meters below the sea surface.

Upwelling occurs when the shoreline is to the right of the alongshore wind in the southern hemisphere and to the left of the alongshore wind in the northern hemisphere. The water that the wind puts into motion is deflected away from the shore by the Coriolis force (the force of the Earth's rotation). Since the surface waters are flowing away from the shore, a shoreward return flow of deeper water is set up to fill the gap. In stratified coastal waters, where a colder layer of water lies a few dozen meters below a warmer surface layer, the deep waters that are churned up to the surface bring with them vital nutrients, like phosphate and nitrate. These nutrient-rich, cool waters nourish microscopic plants, and in turn the fish that feed upon those plants.

The quintessential prevailing winds are the trade winds of the Pacific and Atlantic subtropical oceans, which blow steadily westward and slightly toward the equator at average speeds of around 11 to 13 miles per hour. The trade winds (named centuries ago by sailors on trade ships crossing the North Atlantic, because of the helpful push the winds gave them on westward treks) are found at around 30 degrees north and 30 degrees south latitude, sandwiched between a band of low pressure near the equator and high pressure belts in the middle latitudes. In the high pressure regions at the eastern edge of the ocean basins where the winds originate, the climate is typically hot, sunny, and dry (Baja California, for example); as the winds move westward across the oceans, they gain moisture, which is eventually dumped on the islands at the western side of the ocean basins.

At that western edge, the winds turn first toward the poles, and then loop back east to become prevailing westerlies (winds flowing to the east from the west). These westerlies are responsible for the far better surfing on the Pacific side of North America compared to the Atlantic side. In the Pacific, the westerlies blow in the same direction as waves rolling toward shore from storms out at sea, building up their height; in the Atlantic, the prevailing winds blow against the incoming waves, shrinking them down to unsurfable sizes.

-- By Kathy Svitil

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