Dave Gorjup <dgorjup_at_cox.net> wrote: >>I wasn't perpetuating a myth, just using a common natural event to illustrate a point. If you look at the bottom paragraph in the web page you cited you will see that low barometric pressure is an important component of storm surge. The first part seems to gloss over atmospheric pressure so if you don't read the whole page you miss a good bit. In any event, the question was, does barometric pressure have an effect on sea state? The answer is yes, it does. BTW, a standard day is defined as 29.92 inches at 70 degrees F. I'd like to see a more factual definition of the height of water rise in a low pressure center than a comparison of water vrs mercury density. There's a good bit more to it than that.>> I should have been more explicit. There is a very small rise in local sea level in direct response to a drop in air pressure. The density of water is 13.6 times smaller than that of mercury. That makes it easy to calculate what the rise will be: a column of water that exerts the same pressure as 29.92 inches of mercury will be 13.6 times 29.92 inches (about 407 inches = 33.9 feet of water). Consequently, if local air pressure __drops__ by an inch of mercury, then the local sea level will rise by 13.6 inches of water. That's the effect Dave and others described. That's no myth. It is, however, very small, albeit enough to drown out your campfire if you have it no higher than a foot or so above the surface of a large lake or sea. The myth is that larger rises are directly due to the local air pressure. Read that web site again and you'll find that it is the __wind-generated waves__ associated with a storm center that cause the much larger (many feet -- sometimes up to ten feet) rise called "storm surge." And, that rise is __not__ at the center of low pressure, it is off to the side. In addition, a big surge demands a specific type of local shore : shallow slope. One could say that the low pressure caused the surge, but it's really the effects of the storm. Wind-generated waves from a distant source can cause the same effect, so the local ari pressure can remain relatively constant while a surge occurs. Hope that sorts it out. -- Dave Kruger Astoria, OR *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************Received on Fri Dec 27 2002 - 02:27:45 PST
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