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Gulf Currents That Turn Storms Into Monsters
From: David Farber <dave () farber net>
Date: Wed, 28 Sep 2005 14:06:54 -0400
Begin forwarded message: From: Robert Lee <robertslee () verizon net> Date: September 28, 2005 10:39:09 AM EDT To: dave () farber net Subject: RE: [IP] Gulf Currents That Turn Storms Into Monsters I sail the Atlantic and Caribbean frequently. Most people think when you sail you look only at surface wind. But in fact you very often plot courses to take advantage or minimize the damage from currents and eddies. The Gulf Stream is much hotter than the surrounding water and it can travel at 4 knots. That makes a huge difference depending on whether you are trying to buck it or go with it. A typical 40 foot sailing boat in the ocean might go 7 - 8 knots (water speed, not Speed Over Ground--SOG) in a good wind and still water. If you fight the Gulf Stream you might go only 3 knots and if you go with it you might go 12---a huge difference. The whole mini ecosystem is different. The water of the Gulf Stream is an incredible saturated blue color, it can be 5 or 6 degrees hotter than the surrounding water, to the extent that the wind is against the current the surface is terribly confused, causing sea sickness among even hardy sailors for the time spent on it, and the marine life is vastly different from the waters surrounding it. If you run a trolling fishing line from your stern rail you had better make sure you have light line or you could lose your stern rail. There are also eddies. There are cold eddies and warm eddies. Cold eddies rotate counter clockwise and warm eddies rotate clockwise. These eddies are seen via infrared by satellite and they are typically 50 or 60 miles in diameter and remain in place for up to two years. One navigation strategy is to catch the advantageous edge of an eddy and have it fling you around to where you are headed. It is interesting to see different surface atmospheric conditions that currents and eddies cause. Frequently, as you approach the eastern edge of "the current" (the Gulf Stream) you are met by an astounding wall of discrete squalls, line up like sentinels. They are several miles around. You can see the whole extent of each of them. They are ominous looking and not fun to go through. You try to dodge between them. Because the Gulf Stream is both saltier water traveling over less salty water and hot water traveling over cooler water (it is a heat engine) when it becomes restricted in width, as by Diamond Shoals off Hatteras, North Carolina, you can see it actually rise up. You can see a slope of water, a hill that your boat has to climb up. Inside it is another current, this one cold, coming south, which peters out around Hatteras. The reason so many boats and ships go down off Hatteras is that the shoals create a shallow pool 40 miles out so that surface unrest is magnified. A strong wind blows masses of water in the direction of the wind, due to the coefficient of friction at the surface. In deep water the surface disturbance is minimized, but when the mass of water that is being moved hits shallow shoals the surface becomes frightfully agitated, the sea height goes up (surge) and you can get very high waves with savage slopes, packed closely together. This summer I and my 11 year old son came back from Bermuda and we got caught in the Gulf Stream. It was as if the current had gotten hold of our ankles. We fought to get out of it for hours through the night and into the morning as it swept us northward. It was like glue. With sails up and diesel motor full out when we finally got out we were well north of the mouth of the Chesapeake Bay. In a dozen passages across it I have never seen the current so strong. It was frightening. We had previously been caught at anchor in Bermuda by Franklin and Harvey. These were sub hurricane strength named tropical storms. To be in a boat in a wide open harbor (we could not seek refuge in a small hurricane hole because the storms were coming so close that we could not depend on the wind coming from a particular direction) with winds up to 65 miles per hour for 12 - 18 hours is a frightening experience and I cannot begin to imagine what being hit by 150 miles per hour winds would be like. The force of wind and water, on the water, at 65, is terrifying. Anchor lines can chafe through in minutes. I can imagine that even if you tied your boat to a marine buoy with steel chain that a 150 miles per hour wind would simply rip the cleats out of you boat. -----Original Message----- From: David Farber [mailto:dave () farber net] Sent: Tuesday, September 27, 2005 3:07 PM To: Ip Ip Subject: [IP] Gulf Currents That Turn Storms Into Monsters Begin forwarded message: From: Sashikumar N <sashikumar.n () gmail com> Date: September 26, 2005 8:55:28 PM EDT To: dave () farber net Subject: Gulf Currents That Turn Storms Into Monsters Reply-To: Sashikumar N <sashikumar.n () gmail com> Prof Dave, This article has interesting information on the phenomena of loop currents in Gulf of Mexico, that might aid the mere tropical storm into huge hurricanes. http://www.nytimes.com/2005/09/27/science/earth/27loop.html more links: http://oceanexplorer.noaa.gov/explorations/islands01/background/wind/ wind.html http://www.horizonmarine.com/ew_descript.html regards sashi ------------------------------------- You are subscribed as robertslee () verizon net To manage your subscription, go to http://v2.listbox.com/member/?listname=ip Archives at: http://www.interesting-people.org/archives/interesting-people/ ------------------------------------- You are subscribed as lists-ip () insecure org To manage your subscription, go to http://v2.listbox.com/member/?listname=ip Archives at: http://www.interesting-people.org/archives/interesting-people/
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