It is easily overlooked that weather originates in the sea. There is still a school of thought that says winds cause waves, and storms affect the ocean. But it is really the other way around. It is odd that what mariners seem to know, meteorologists are still confused by.
Few sailors have experienced a violent storm over a calm sea, but plenty will tell tales of how the sea dramatically changed prior to a storm. Usually there is only just enough warning to enable the battening down of hatches. It is the increasing swell that warns of impending rough weather and the approaching extreme conditions. The ocean causes changes to the air, so it cannot be the air that creates the swell.
Most weather originates in the oceans, most rain comes from the sea surface, and most drops back into it. Giant weather systems pass from ocean to ocean around the globe. They cross land to reach the next mass of water. The land plays a very minor part in weather production, and is causally almost negligible. The rain forests, in size or numbers in no way affect global weather patterns, neither do vehicle emissions. There was violent weather long before there was any vegetation on earth, and storms came and went well before cars.
Recent research has shown that deep within the ocean, waves as tall as skyscrapers and with crest to crest wavelengths of about 100 miles move at around 5mph around the globe. The size of deep current waves has taken recent researchers by surprise. At the ocean surface, swells have wavelengths of only a few hundred metres, so observed swells can not come from distant storms - they must be generated from below.
These oceanic ‘Internal waves’ move just like those breaking on a beach, but are larger and slower, as well as being located deep in ocean masses. Internal tides wash back and forth across undersea mountains. They can be created at any depth and the forces created by that movement spawn underwater waves that can travel great distances through the ocean's interior.
A good analogy is in the flicking motion of a stock whip. The oscillating differential at one end produces travelling waves that continue the length of the trajectory. Those waves have crests that look like the waves on the surface of the sea. Underwater crests are not visible but contribute to what becomes swell. What separates swell from waves is simply the depth difference between the deep current crests and those closer to the surface.
An example of the skyscraper-sized waves, which can be about 1000 feet high, are those that form around the underwater mountain chain - the Macquarie Ridge - south of New Zealand and take around one week to travel 1,500 miles (2,414km) to the southeast coast of Tasmania, before breaking on the continental shelf – the 'ramp' of rock before the shore. The wave-breaking and turbulence that result from this impact happens far below the often stormy sea surface. The turbulent mixing that occurs in the deep sea off Tasmania and other sites is sufficient to affect the overall circulation of the global ocean.
The global circulation of the ocean features cooling of surface water in the North Atlantic and around Antarctica. Cold water sinks to the bottom of the ocean and travels towards the equator up the western side of South America and down from N America. They meet at the giant concave bay formed by Columbia and Panama which creates a launching platform for currents to lurch westward along the equatorial band. Near the surface, warm water driven by higher pressures moves towards the poles to replace the water that has sunk - the Gulf Stream is one of these warm surface currents. At the surface near the equatorial band, currents flow westward. The air interfaces with the ocean surface and becomes the pattern we call La Nina
Sharks are said to be attuned to the pressure changes in water and tend to swim deeper into the ocean when they sense a storm brewing. That means an undersea storm. Dolphins search the surface for fish running ahead of underwater turbulence, which explains the old folklore about the sight of dolphins warning of impending weather change.
Undersea currents have been realised for centuries, and have been labelled conveyer belts. El Niño is a reversal of an ocean current between the west coast of South America and the east coast of Australia. Currents mix marine life and provide nutrients for the creatures that inhabit the ocean, which are 99.9% of the biomass of the planet. Many marine creatures, such as eels, use currents to relocate thousands of kilometres in order to spawn.
As everything on earth is in flux, so too is the sea. Currents are instigated by the combination of the orbiting moon and the rotating earth. Undersea vents, emissions and eruptions provide temperature differences in parts of the ocean, producing thermoclines, as well as propelling and up-swelling the massive flowing of underwater waves. Hills and ranges modify and magnify the underwater flows in the same way that winds are deflected by hills and ranges on land.
But the terrain in both sea and on land does not create the waves. No study of the causes of weather and climate can be complete without the chartering of what causes, controls and influences the wave systems in the ocean. It has thus far been a neglected area of study. As the moon monthly crosses hemispheres of ocean 250,000 miles away, great volumes of water and air are transferred across the equator. When the moon transits in a closer arc to the earth, currents everywhere induce giant waves that result in swells, king-tides, and cyclonic systems above the surface. At the same time under the surface of the land the waves that we call earthquakes become more prevalent.
Ken Ring of www.predictweather.com is the author of the Weather Almanac for NZ for 2015 (Random House)