MadSci Network: Earth Sciences

Re: Hurricanes

Area: Earth Sciences
Posted By: Shel Randall, System Consultant
Date: Mon Aug 26 18:47:38 1996
Message ID: 839960574.Es

> How do hurricanes form?
> What's the difference between tornadoes and hurricanes?
Danny -

The exact process that leads to the formation of hurricanes is not clear, but there are some pretty good educated guesses:

The spinning of the Earth creates natural turbulence in the atmosphere. There are large volumes of warm and cold air that are constantly running into one another creating clouds, rain and storms. Since water is a liquid that retains its temperature well, the presence of water near a storm keeps the air masses from equilizing their temperature, and the storm can become stronger.

When the Earth spins, it has an "angular momentum" which gets passed on to almost everything in motion on the surface of the Earth. When things fall or rise a great distance they tend to move in a rotating path.

In the Northern Hemisphere of the Earth, low pressure areas in the atmosphere caused by the turbulence pulls air downward into the area and because of the spin of the Earth, this air moves generally counter-clockwise.

When there is a lot of air turbulence moving and spinning and being strengthened by moisture, a spinning vortex of air is formed.

Over the ocean, where water is most abundant, these spinning masses can become enormous, affecting the weather in all directions for hundreds of miles. These are called hurricanes.

Over the land, where the water is far less abundant, the spinning turbulence rarely gets over a mile wide and can pass within a mile of a location in a dark storm without being detected. The water feeding a tornado usually comes from the moisture in the air during a thunderstorm.

For contrast, here are some basic differences between hurricanes and tornadoes:

Property                Hurricane               Tornado
---------------------   ---------------------   ------------------------
Range of Windspeed      75 - 150+ mph           60 - 250+ mph
Distance of Effect      Hundreds of miles       A few miles
Location                Over the ocean          Over land
---------------------   ---------------------   ------------------------
For more information, check out these websites:

Hurricane Terminology
Tornado Formation
FEMA (Federal Emergency Management Agency) Tornado Fact Sheet

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