Re: Winter on the Amazon

["William Vannerson" <William_Vannerson@ama-assn.org>]

FWIW,  In today's Chicago Tribune, Tom Skilling explained why there are almost no huricanes in S.A.  It has to do with earth's rotation and a force.  I've pasted it below.
Dear Tom, 
Can you explain why the big Atlantic storms don't hit the northern part of South America? Tropical cyclones always seem to move north toward the Caribbean or up the United States' Atlantic coast. 
Rick Nally, Naperville, IL 
Dear Rick, 
Hurricanes tend to form over warm waters between 5 and 20° north latitude. A sizeable piece of the north coast of South America sits south of this zone. The physics of earth's atmosphere is behind the rarity and, at many locations, the total absence of hurricanes and tropical storms there. Parts of Venezuela and Columbia have experienced the fringe effects of such storms—but infrequently. (The flooding we hear about in those countries is driven by tropical disturbances unlikely to include the large scale, rotary winds found in hurricanes). The reason that’s so is that at latitudes close to the equator, the critical Coriolis force, driven by earth’s rotation, tapers to near zero. It's the Coriolis force which is behind the rotary winds of hurricanes and other weather systems away from the equator. With much of South America’s northern coast close to the equator and the Coriolis force there negligible, winds won't spin. In rare cases, hurricanes have moved across the equator, but they quickly diminish in the process.


Bill Vannerson
McHenry, IL
http://ourworld.compuserve.com/homepages/william_vannerson



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