WIND DRIVEs WAVES
The uneven heating of the Earth's surface also creates differences in atmospheric pressure, which drives the winds. Surface pressure is low in warm equatorial regions and high in cold polar regions, thus creating a pressure gradient movement from the poles to the equator. This pressure gradient movement from the poles to the equator can be visualized as a skier carving down a mountain slope or a surfer slicing down a wave's face. High to low the saying goes. High pressure wants to move to low pressure just like the surfer down a mountain of water. This pressure gradient force drives winds, causing a flow of surface wind from the poles to the equator. (See Wind Circulation image.)
The circulation would be complete if it wasn't for the fact that the Earth rotates. When the Earth spins, it bends or curves these winds. To illustrate, jump on a merry-go-around and try to throw a ball to your buddy on the other side. The ball goes straight while your buddy moves with the spinning merry-go-around.
On a planetary scale, this is called Coriolis Force.
The Coriolis Force affects airplane flights as well as planetary wind circulation. Contrary to popular belief, it does not make your toilet water flow in the opposite direction south of the Earth's equator. (See Coriolis Force image.)
But, that is not all. Read on because our little planet is going to make things even more interesting.
The general circulation of air is from the poles to equator at the surface and then from equator to poles aloft. However, in the Northern Hemisphere, the Coriolis Force turns the returning southerly flow of air to the right (westward) at about 60 degrees latitude, and it turns the upper northerly flow of air from equator to poles to the right (eastward) at about 30 degrees latitude. The opposite deflection happens in the Southern Hemisphere. The wind deflection at the 30 and 60 degree latitudes block the flow of air between the equator and the pole. The air piles up at these latitudes. The Earth's restless nature cannot live with this unbalanced condition. Huge masses of air churn up, plunge, and break through the barrier. Storms develop. These storms also drive the winds.
As these winds flow over Earth's oceans, the tension between the moving air and the surface of the water causes waves. This tension disturbs the ocean surface, creating small rounded capillary waves, commonly called ripples. Again these two fluids—air and water—seek out equilibrium to restore the oceans smooth surface. As this ripple action increases, however, the balance is tipped and the water "catches" more wind, transferring more moving energy from the wind to the ocean. This energy moves through the ocean as a wave.
The water is not moving forward as in a current, however. Instead, the energy moves, rolling through the water in a circular motion eventually forming gravity waves. Once the balance of energy is tipped in the ocean's favor, the waves move faster than the wind, becoming elongated. We call them swells.
As these swells move to shore, they begin to "feel" the rising floor. This process is called shoaling. As the bottom rises or shoals, the waves orbital (circular) energy gets squeezed and flattens. The waves slow down and bunch together, decreasing their wavelength, but the time between wave crests stay the same. The height of the waves grow until one by one each becomes unstable and literally topples over, releasing energy onto the beach. This transfer of energy is part of our little planet's quest for establishing equilibrium.