|MadSci Network: Earth Sciences|
Hi Ellen, That is a great question, and it actually raises two issues. First, yes, the ocean exhibits many of the same "weather" patterns as does the atmosphere (although it doesn't really snow much... and no lightning). These patterns are driven by the same forces that drive atmospheric weather, but they happen over different time scales. This being true, however, oceanic "weather" patterns will look much different from what you see in the atmosphere. To start, you need to have a decent understanding of how weather works in the atmosphere. A starting point is http://en.wikipedia.org/wiki/Weather , and http://en.wikipedia.org/wiki/Wind. The fundamental thing to understand is that atmospheric weather is driven by differences in density between masses of air. Usually, this is due to temperature differences; for instance, air over warm parts of the ocean gets less dense, causing it to rise... this leads to pressure differences between warm air masses and cold air masses. The "fronts" that you see on a weather map are areas where warm and cold air masses meet. Because different air masses are at different pressures, air will flow from areas of high pressure to areas of low pressure. Because the earth is rotating, the Coriolis effect will change the direction of air movement (turning it to the right in the northern hemisphere, to the left in the southern). These basic processes driving weather are fundamental to fluid mechanics. As such, exactly the same processes happen in the fluid that makes up the oceans. Water of different temperatures will have different densities, for instance, cold water near the poles sinks, driving bottom currents. Another big driver of water moving around in the oceans is atmospheric winds blowing over the surface... in this way, the ocean and the atmosphere are tightly connected; remember, the temperature of the ocean water helps to drive the winds. Large eddies of ocean currents look very much like hurricanes blowing through the atmosphere. Some important differences, though, have to do with the response times of the air vs. the ocean. Ocean water is almost 1000 times as dense as air, so it takes much longer to respond to changes in pressure. It also has a much higher heat capacity, so it doesn't change temperature rapidly. Additionally, water absorbs most of the sunlight that hits it, so you don't get the same situation as in the air, where the sun warms different surfaces to different temperatures, driving local changes in air temperature and therefore winds. All of these factors mean that weather events happen much more slowly in the ocean, and last much longer. A giant ocean eddy can last months to years, while a massive weather event like a hurricane might last only a few weeks. Winds in the atmosphere can blow at 1000s of meter/sec (100s of mph), while the Gulf Stream, the fastest ocean current, moves about 2 m/sec (about 5 mph). Just as atmospheric weather conditions bring rain to plants, oceanic weather brings nutrients to the organisms that live there (see : http://www.whoi.edu/oceanus/viewArticle.do?id=10592 ) Finally, your question asks about whether tsunamis are a type of weather event. Actually, tsunamis are very different from any of the things I've mentioned. Tsunamis are caused when an external event triggers a massive change in pressure over a very local scale. Wikipedia has a good page on what causes a tsunami ( http://en.wikipedia.org/wiki/Tsunami ). Basically, it is an instantaneous event which displaces an enormous mass of water (thereby putting a huge amount of energy into the ocean). This is much different from weather events which are driven by small temperature and density differences within the air or ocean. The only atmospheric phenomena that would be similar would be a bomb going off, an airplane breaking the sound barrier, or a volcano erupting... maybe a Who concert would qualify... none of these events are a part of normal weather patterns any more than tsunamis are a component of general ocean weather. I hope this helps. Moose O'Donnell
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