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Hurricane, Cyclone, Tornado: Definitions and Differences

written by: ciel s cantoria•edited by: Donna Cosmato•updated: 3/29/2012

How do storms form, and what is the difference between a hurricane, cyclone or a tornado? Explore the atmospheric elements that have to be in place for each of these storms to occur.

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    Atmospheric Processes that Give Rise to Weather Disturbances

    800px-Simple Water Cycle 

    Studies of the Earth’s atmosphere provide information on how the Earth’s natural processes result in different weather conditions and phenomena. Certain atmospheric processes, like the transfer of heat energy and water moisture, are capable of giving rise to turbulent weather disturbances that visit our regions in the form of hurricanes, cyclones, or tornadoes. Definitions and differences between each weather phenomenon are easier to understand if we know how these processes take place.

    The transfer of heat energy referred to here is about the sun’s radiation and how it transports energy via electromagnetic waves. This type of energy creates air pressure as it heats up the vast ocean, and other bodies of water. It is the initial phase of an atmospheric process, which we know as the water cycle, wherein water is vaporized when heat energy touches the ocean’s surface. This means that part of the water breaks down into its gaseous form and combines with all the other gasses already present in the atmosphere. Some of these gasses will later form clouds, and precipitate into water, which falls back to Earth in the form of rain.

    While these two aspects of heat energy and moisture transfers take place, some molecules create air masses and air parcels, in large or small scales. Vertical motions, originating from radiated energy, create air pressures that cause these air masses and air parcels to surge-up. As the Earth rotates, the sun’s heat lessens; hence, the air pressure naturally goes downwards. Air pressure is constant in the atmosphere, but tends to ascend (high) or descend (low), depending on the amount of electromagnetic waves that hit the Earth. The following sections describe how weather is associated with high and low pressure areas.

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    How the Earth’s Rotation Affects the Air Pressure in the Atmosphere

    Earth Global Circulation CAT 

    Recall that the Earth creates energy by the spinning motions it makes while about its axis, and this energy gives rise to the ocean’s currents and global winds. However, these global winds meet up with air pressure as the latter rises and falls. As wind and pressure meet, the winds spiral around the air molecules. What happens next is determined if wind and air molecules will converge at high pressure or low pressure points.

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    What Happens if Wind and Air Molecules Converge at High Pressure?

    800px-Fihalhohi ocean view 

    The higher the air pressure, the less the mass or amount of air molecules is in its system, which means air pressure has thinned out. As the winds spiral around the thin air pressure at high temperature, it can deflect the pressure’s upward movement into a downward movement, and its inward spinning motion into a counter-clockwise or outward spinning direction.

    It becomes a mass of descending and less dense air, spreading out through the Earth’s atmospheric layer, and stabilizes the atmospheric condition. It can cool down the Earth’s temperature, thus preventing too much heat transfer that causes water to vaporize and air molecules to rise. The Earth’s populace then experiences fair weather conditions, under a blue and less cloudy sky.

    However, if this condition persists for an abnormally long period of time, it can also result in a dry-spell. Most of the water stays in the vast ocean instead of vaporizing and precipitating into rain, as a way of distributing water on land. In other parts of the world, the Earth’s surface remains cold, because the sun’s radiation is being blocked by the large amount of air molecules that blankets the Earth’s atmospheric layers.

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    What Happens if Wind and Air Molecules Converge at Low Pressure?

    Cyclone Mala 

    If global winds meet with the air molecules at the low pressure, the force of the spiraling wind will not be able to interfere with its upward and spinning movement. This is because the air pressure is still filled with masses of air molecules and air-parcels. The winds will instead be drawn-in and become trapped inside the low pressure system, but continue with the spiraling or spinning movements. The masses and parcels of air molecules, likewise, combine with the trapped wind while this entire low pressure convergence continues to rise. This particular occurrence is called a depression, or cyclone.We are now ready to understand the definition of this atmospheric phenomenon.

    Please proceed to the next page for the definitions and differences of hurricane, cyclone and tornado.

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    Know what a tropical cyclone is and learn how and when they become a hurricane. This article will finally clear out all your confusions about the differences between a hurricane, cyclone and tornado.
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    Definition of Cyclone and its Difference

    A cyclone occurs when massive winds produced by the rotation of the Earth spiral around a low pressure area which built-up over a heated part of the ocean, usually near the equator. The spiraling wind gets drawn-in into the low pressure and converges with large masses of air molecules and vaporized water. The inward spinning movement of the wind continues, while accelerating in speed and causes the low pressure to rise higher. The rapidity of the spinning motion creates a vacuum at the center where there are no rains or clouds and is called “The Eye". As rapidly spiraling wind and air molecules hover above the ocean, the convergence draws in more air and moisture from the solar-heated ocean water, thus carrying with it heavy rains as it travels, and it is called a tropical cyclone.

    If the tropical cyclone sustains a maximum sustained surface wind of less than 17 m/s (34knots, 39mph), the tropical cyclone is called a tropical depression. However, if the tropical cyclone reaches at least 17 m/s (34kt, 39mph) it becomes a tropical storm. If the sustained surface wind reaches 74 mph (or 64knots, 119kph) or more, the tropical cyclone will either be called a hurricane or a typhoon, depending on the direction it takes as it travels.

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    Definition of Hurricane and its Distinction from other Forms of Tropical Cyclone

    800px-Atlantic hurricane tracks hurricane destruction 

    A hurricane is a tropical cyclone whose rotating winds spin in a counter-clockwise movement and travels towards the Northern Hemisphere. This will be in the direction of the North Atlantic Ocean, or the Northeast Pacific Ocean, east of the international dateline, or the South Pacific Ocean, east of 160E. It has hovered above a tropical ocean long enough to gather or suck –in massive amounts of water moisture to produce torrents of rain. The accelerated speed of its spiraling wind can let out violent gusts of air, wherein both rain and wind are capable of wreaking havoc and immense destruction. Some examples of countries found in the Northern Hemisphere are Europe, North America, and some small portions of South America.

    A hurricane is different from a typhoon, which is also a tropical cyclone, and whose rotating winds spin in a clockwise movement and will travel towards the Northwest Pacific Ocean, west of the international dateline. It also carries with it violent gusts of winds and torrential rains strong enough to create damage in every area it crosses.

    A tropical cyclone may travel to other parts of the world with the speed of 74 mph (or 64knots, 119kph) or more, and is called by other names like, “tropical cyclone" if going to the Southwest Indian Ocean, or “severe tropical cyclone" if in the direction of the Southwest Pacific Ocean west of 160E or Southeast Indian Ocean east of 90R; or “severe cyclonic storm" if in the direction of the North Indian Ocean.

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    Definition and Difference of a Tornado

    800px-F5 tornado Elie Manitoba 2007 

    A tornado is a concentration of global winds, which spins inside a low pressure area. It possesses such powerful strength that its swirl can form into a massive column of wind, which looks like a huge black funnel. The whirling wind inside a tornado’s spiral moves upwards and downwards and creates a vacuum inside the column. The vacuum is capable of sucking-in anything that crosses its path through its tail. Although the wind inside has a speed of 500 mph, it normally travels at about 300 mph. Some tornadoes can spawn smaller tornadoes, although scientists are still unsure how a tornado is formed. Some storms are capable of creating tornado-like funnels but they hardly touch the ground surface.

    Similar to tropical cyclones, a tornado that travels towards the Northern Hemisphere spins with counterclockwise movements, while tornadoes that travel towards the Southern Hemisphere spins clockwise.

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    Reference Materials

    • http://www.atmosphere.mpg.de/enid/1__Weather___Fronts/-_Pressure_systems_15y.html
    • http://www.ucar.edu/learn/1_1_2_7t.htm#background
    • http://www.britannica.com/EBchecked/topic/606551/tropical-cyclone
    • http://www.atmosphere.mpg.de/enid/1__Weather___Fronts/-_Pressure_systems_15y.html
    • http://www.ucar.edu/learn/1_1_1.htm
    • http://tornado.sfsu.edu/geosciences/meteorology.html
    • http://www.aoml.noaa.gov/hrd/tcfaq/A1.html
    • http://library.thinkquest.org/C003603/english/tornadoes/whatisatornado.shtml
    • http://library.thinkquest.org/10136/cyclones/cycltq.htm
    • http://www.aims.gov.au/pages/research/project-net/cyclones/cyclone-01.html
    • http://www.nasa.gov/worldbook/hurricane_worldbook.html

    Images from Wikimedia Commons