From our perspective, stationary objects are just that, unmoving. It also influences the movement of ocean currents. Scientists refer to this bending as the Coriolis Effect.
It is easiest to understand this phenomenon when thinking about travel in a northern or southern direction. As you get closer and closer to the poles, the distance traveled in one rotation gradually shrinks until it reaches zero at either pole. Therefore, an object on the surface will gradually spin slower the closer it gets to a pole. But leave the surface of the planet, and the anchor keeping you in sync with the land beneath you disappears.
Any moving object plane, boat, hot air balloon, water will begin its travels at the rotating speed of the location where it took off from. If it should travel north or south, the ground beneath it will be traveling at a different speed.
Travel North from the Equator, and the ground will gradually spin slower beneath you. This causes an object attempting to travel in a straight line to veer to the right in the Northern Hemisphere and veer to the left in the Southern Hemisphere relative to the direction traveling. Understanding how the rotating Earth affects movement to the west or east is a bit trickier.
Envision an elastic string attached to a ball on one end and an anchored point at the other. The faster the ball is spun around the anchor, the more the elastic stretches and the farther the ball travels from the center point.
An object traveling on Earth behaves the same way. If the object moves east, in the direction that Earth is spinning, it is now traveling around the axis of Earth faster than it was when it was anchored—and so, the object wants to move out and away from the axis. Still tethered by gravity, the object does so by moving toward the equator, the place on Earth that is the greatest distance from the axis. It does so by moving toward the pole. This again appears as a bend to the right in the Northern hemisphere and to the left in the Southern hemisphere.
In the Northern Hemisphere, surface water curves to the right and in the Southern Hemisphere it curves to the left of the direction it is forced to move. There are 5 major gyres—expansive currents that span entire oceans—on Earth. Similar to surface waters, Northern gyres spin clockwise to the right while gyres in the south spin counterclockwise to the left. The center of the gyres are relatively calm areas of the ocean. The Sargasso Sea, known for its vast expanses of floating Sargassum seaweed, exists in the North Atlantic gyre and is the only sea without land boundaries.
Today, gyres are also areas where marine plastic and debris congregate. The most famous one is known as the Great Pacific Garbage Patch , but all five gyres are centers of plastic accumulation. Wind moving across the ocean moves the water beneath it, but not in the way you might expect. The Coriolis Effect, the apparent force created by the spinning of Earth on its axis, affects water movement, including movement instigated by wind. Recall that Coriolis causes the trajectory of a moving object to veer to the right or the left depending upon the hemisphere it is located in.
Wind blowing over water will move the ocean water underneath it in an average direction perpendicular to the direction the wind is traveling. As wind blows over the surface layer of water, friction between the two pulls the water forward. The top most layer of water will bend away from the direction of the wind at about 45 degrees. For simplicity, we will assume that this scenario is in the Northern Hemisphere and all movement bends to the right. As the top layer of water begins to travel, it in turn pulls on the water layer beneath it, just as the wind had.
Now this second water layer begins to move, and it travels in a direction slightly to the right of the layer above it. This effect continues layer by layer as you move down from the surface, creating a spiral effect in the moving water. In addition to a change in direction, each sequential layer down loses energy and moves at a slower speed. Friction causes the water to move, but drag resists that movement, so as we travel from the top layer to the next, some of the energy is lost.
When all the layers down the spiral are accounted for, the net direction of the water is perpendicular to the direction of the wind. The ocean is connected by a massive circulatory current deep underwater.
This planetary current pattern, called the global conveyor belt , slowly moves water around the world—taking 1, years to make a complete circuit. It is driven by changes in water temperature and salinity, a characteristic that has scientists refer to the current as an example of thermohaline circulation. Saltier and colder water is heavier and denser than less salty or fresher , warmer water. Around the globe there are areas where the heat and saltiness of ocean water and therefore, its density change.
The most important of these areas is in the North Atlantic. As warm Atlantic water from the Equator reaches the cold polar region in the North via the Gulf Stream, it rapidly cools. This region is also cold enough that the ocean water freezes, but only the water turns to ice. As the water freezes it leaves the salt behind, causing the surrounding water to become saltier and saltier. The cold, salty water then sinks in a mass movement to the deep ocean.
It is this sinking that is a main driver for the entire deep-water circulation system that moves massive quantities of water around the globe. Cooling also occurs near Antarctica, but not to the extremes that happen in the Northern Hemisphere. In this area, evaporation is the main driver that changes the salinity of the ocean water.
But I am also a physical oceanographer and climate scientist at Brandeis University. Waves in the ocean act similarly. On rare occasions earthquakes and landslides can generate waves, but usually waves are created by wind. Generally, the biggest and most powerful wind-generated waves are produced by strong storms that blow for a sustained period over a large area. Think for a few seconds about what happens when you throw a stone into a serene pond.
The waves that surfers ride originate in distant storms far across the ocean. The waves within a storm are usually messy and chaotic, but they grow more organized as they propagate away from the storm and faster waves outrun slower waves.
When describing a swell, oceanographers and surfers generally care about three attributes. First, the height — how tall a wave is from the bottom to the top. The wave transports energy, not water. An analogy is a crowd of people doing a Mexican wave in a stadium: they stay in the same location, but the wave they create travels around the arena. As waves reach the shore , the shallow floor begins to run into their base, slowing their deeper parts.
This causes the wave to stand up then pitch forward before eventually breaking. For the generation of massive waves, scientists study the underwater topography of the ocean floor. They also use bathymetry, which is the measurement of the depths of oceans and other large bodies of water. They use these data along with satellite technology to monitor and predict when and where these massive waves will hit.
Finally, surfers use their knowledge of the physics of these big waves to learn how to catch the ultimate ride. What gets them started? Use as many words found in the segment for you descriptions. Stretch it out and vibrate the first coil and observe how a wave travels back and forth. Think about what they need to understand about the physics of big waves to survive. Be sure to describe the geography and the topography of the ocean floor in these areas.
What do surfers need to know about the science of waves to be able to catch the perfect wave? Be sure to describe how surfers use their knowledge of gravity, momentum, and balance to ride their surf boards. Introduction to Waves , National Geographic Xpeditions.
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