Hurricane Dennis

Photo courtesy of NASA.
In the realm of weather phenomena, the hurricane has no equal when it comes to inspiring awe and fear in the minds of us humans. These gigantic storms can span a thousand miles or more with winds well over 100mph. The destruction left behind after a hurricane has passed over a land mass can destroy lives and empty national treasuries in just a few hours.

But the detrimental effects of hurricanes aside, when viewed from space they are among nature's most beautiful creations. The buffeting winds and clouds spinning around a tightly defined "eye" appear to be moving in slow motion from many miles above the earth, masking the devastation that is often taking place below them. A perfect example is the subject of today's picture, Hurricane Dennis, just before it made landfall on the Gulf coast of the United States on July 10.

Hurricanes are rotating areas of intense low air pressure that form over warm waters (at least 80 degrees Fahrenheit). The rotation of the earth is the catalyst that causes the low pressure area to start spinning (a phenomenon called the Coriolis effect). The resulting disturbance is called a tropical storm until the winds reach 74 miles per hour, at which point it becomes a hurricane.

All low-pressure systems, including tropical storms and hurricanes, spin counter-clockwise in the northern hemisphere and clockwise in the southern hemisphere due to the nature of the Coriolis effect. Low pressure systems cannot start spinning within 2 degrees of the equator because the Coriolis force is too weak to set the air mass into motion.

In North America, we call these awesome storms hurricanes. In the western north pacific region they are called typhoons, and they are referred to as tropical cyclones in the Indian ocean and the western South Pacific.

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