Atmosphere And Weather
Hurricane Isabel

Tropical Cyclones and how they Occur

Hurricane Isabel
Effie Moore Salem's image for:
"Tropical Cyclones and how they Occur"
Caption: Hurricane Isabel
Image by: unknown
© creative commons

Tropical cyclones, huge wide masses of spiraling winds with calm interiors - the eye of the storm - form over warm oceans in northern Australia, East Asia and near many islands in the Pacific. In the far East, these same storms are known as typhoons; in areas of warm comparative areas of North America, in the Atlantic ocean, they are hurricanes.  

For these to form, the top layer of the underlying ocean or water system must have a temperature of at least 26 C. With the heat from such warm, moist areas, drifting upward, forming clouds, cyclones may be the end result. At first, massive thunderstorms develop, and as intensity increases, a tropical storm develops and picks up speed.

Then, if it doesn't weaken as it blows out over land or over colder regions of the ocean, it builds into a cyclone, a hurricane, or a typhoon, depending on the geographical region. What causes the circling motion of the storm? Why not simply a frenzied ferocious wind blowing according to the pressure behind it?

The spiraling force, the Coriolis effect, is caused by the rotation of the earth. In other words, as the winds are pushed forward, they are resisted and pushed back and swirl according to the strength of the wind behind them. In the southern hemisphere the deflection of the heated air moves to the left, in the northern hemisphere, it is deflected to the right of the Coriolis force and will "spin" counterclockwise. Those in the southern hemisphere will spin clockwise.

Speed of the wind will determine the amount of deflection. This translates into a highly uniform spiraling cyclone or as with a tropical storm, a more loosely formed spiral. All tropical storms form in the same way, and the only difference will be in the tropical area they develop, the summer season that spawns them, and the slight difference of the Coriolis effect of either being from the right or the left, and their clockwise or their counterclockwise spin.

Areas nearer the equator spawn storms that eventually turn into tropical cyclones more frequently. Cumulonimbus cloud formations are indicative of cyclones. These are part of the wind machine that blows, picks up speed and eventually wears itself out as it dissipates into areas less conducive to storms.

During hurricane season the center of this spiral, the eye, is calm and often well-trained meteorologists, with an equally trained pilot, will fly into these areas to survey and to report on the storm. While this is a risky business indeed, it does make for inspiring and adventurous weather predictions. As long as they stay in the cooler areas of the mid section, they are perfectly safe.

To get a clearer picture of a circling cyclone, one must understand how it begins. Picture a vapor from a tea pot with its hot steam being emitted into a room. The teapot has a narrow route of escape of hot air. That is easy to understand. Inside a vessel with a wide open top the hot water also must escape upward and it does so, probably in a straightforward, upward effect. But should the pot be on a tilting rotating stove burner, the spiraling effect would happen. At least that is a crude illustration of a tropical cyclone.


More about this author: Effie Moore Salem

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