[IP] Gulf Currents That Turn Storms Into Monsters

[David Farber <dave@farber.net>]

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


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