Cyclones

1. Cyclones GMS satellite image on 9 January 1992 showing Typhoon Axel in the northwest Pacific and Cyclones Mark and Betsy in the southwest Pacific. Bureau of Meteorology Following information taken from: http://ntlapp.nt.gov.au/tracy//advanced/Met/cyclones.html (Australian governmental department and mapsoftheworld.com

2. What are cyclones? • A Cyclone is a closed area of circular rotating fluid, clockwise in the Southern Hemisphere and Counterclockwise in the Northern Hemisphere • It arises due to low atmospheric pressure

3. Types of cyclones: • Cold core cyclones depends on the trough it is formed in • Warm core cyclones forms in the upper level of the trough • Extratropical cyclone is a totally different type of atmospheric disaster, which lacks both tropical and polar features. It is observed outside the tropical zone. Extratropical cyclones are primarily centered around mid-latitude. • Polar low is relatively less severe in nature. It is very common in north and south poles • Mesocyclone is a special type of cyclonic whirlpool that accompanies other severe weather conditions like tornadoes, supercells and thunderstorm

4. Tropical cyclones • Tropical cyclone depends on the warm core storm system • Most common form of cyclone • Develops due to a low pressure center • Occurs over warm oceans • Comes with powerful current of air, heavy rainfall and severe thunderstorms

5. Formation • Upward movement of warm air. • As the moist air moves up it comes in contact with the cold air in the upper level of atmosphere and gets condensed. • A powerful low-pressure cell is an essential factor for tropical cyclone. A revolving draft with a strong inward current leads to tropical cyclone

6. Based on its location and severity, tropical cyclone is classified as • typhoon, • tropical storm, • cyclonic storm, • tropical depression and • hurricane. • If the velocity of storm wind is not more than 60 kilometers per hour, it is termed as tropical depression. • Tropical storms come with a speed of 60 to 110 kilometers pre hour. • Wind speed associated with tropical cyclones must be more than 100 kilometers per hour. Tropical cyclones, which break out in the eastern part of North Pacific and northern Atlantic regions are popularly known as hurricanes. The same when occurs in the western part of North Pacific, it is termed as typhoon.

7. Hurricanes For a hurricane to form • the temperature of ocean water should not be less than 26.5 degree Celsius. • Moisture and heat developed from the water surface are the main factors influencing the strength of hurricanes. • As the land or ocean temperature falls, strength of hurricane decreases. For hurricane formation the relative humidity of the lower and middle tropospheric level must also be very high. Condensation of vapor reduces substantially due to high relative humidity. This results in latent heat formation due to increased precipitation.

8. The foremost characteristic is that tropical cyclones are most violent of all the atmospheric disturbances. • The average speed is 120 kmph. Although it may vary from 32 kmph to 200 kmph or more. At times it reaches 400 kmph also. • They have closed isobars. The pressure gradient is very sharp. More closely spaced isobars represents greater velocity of the storm and vice-versa. The pressure at the center is extremely low. The winds from the surrounding area are drawn towards this low-pressure core called the "eye" of the cyclone. • Tropical cyclones develop over oceans and seas only. They are most violent and vigorous over water. On landfall, their velocity decreases due to friction, and as the source of energy is cut off, they dissipate soon. Thus they affect the coastal areas only. • The movement of tropical cyclone is affected by the prevailing wind system. Normally they move from east to west under the influence of trade winds. • They are seasonal in nature and occur during a specific period of the year only. In the Caribbean this is June to November