Examine the causes and effects of tropical cyclones. 

Candidates are expected to define the term tropical cyclones, describe the characteristics of Tropical cyclones, state the regions where they occur.  Describe how they are caused and state the effects in the areas across which they occur.

A Cyclone is a low pressure wind system that moves at an averagely high speed of 250km/hr, with a diameter between 80 and 400kms

A tropical cyclone is an intense violent tropical storm that occurs in the tropics particularly along the I.T.C.Z (Inter-Tropical Convergence Zone).

• They occur in tropical oceans, mainly on the Eastern side of the continents between 5° and 20° North and South of the Equator.
• They occur between July and October in the Northern Hemisphere and January to April in the Southern Hemisphere.
• Tropical cyclones have steep pressure gradients with violent winds circulating in wards Anti clock wise direction in the Northern Hemisphere and in a clock -wise direction in the southern Hemisphere.
• Thus Tropical cyclones usually develop/originate from oceans /seas and move towards land masses. They originate on the western sides of oceans and move towards the Eastern sides of continents.

Tropical cyclones are /mown by different Names depending on where they occur

• Hurricanes in Mexico, Caribean. Seas and North Atlantic Ocean.
• Typhoons China, Japan, Philippines and Pacific Ocean.
• Willy- willies on the Eastern Australian coast.
• Tornadoes in USA
• Cyclones in the Indian ocean.·.
• Tropical cyclones occur in all tropical oceans/seas except southern Atlantic

Causes of Tropical cyclones

• Cyclones originate from a local heat source that is in the ocean /sea – surface.
• A wave disturbance is caused /occurs due to differences in the local temperatures and hence pressure differences over the ocean surface.
• A wind begins to cycle around the area of low pressure called the ”EYE”, which is a zone of calm, dear skies and descending dry winds.
• This builds up momentum very strong and violent wind through the process of Cyclo -thesis (convective movement of violet wind) developing a towering Cumulonimbus clouds
• This is because there is a constant supply of moisture from the warm water body/ ocean (the local source of heating)
• It develops a steep barometric gradient in the “LOWS” (low latitudinal areas) giving rise to high speed winds (gusty winds)while the “EYE”‘ constantly develops calm weather conditions.
• Tropical cyclones therefore develop on the ocean surfaces due to maximum instability in the atmosphere
• Tropical cyclonic movements are in the direction of the wind.

Effects of tropical cyclones

Cyclones affect both weather and human activities.

Effects of tropical cyclone  effects on weather are;

• -Cyclones are associated with gusty winds. Winds blow at high speed ranging from 116km/hr to 250km/hr. Tornadoes can reach speeds of500km/hr; such winds are very destructive.
• Cyclones result into thunderous and heavy rainfall full of lightening. At times trees and animals are stroked to death by the lightening
• A combination of dense clouds, torrential rains and very fast winds reduce visibility to a few metres.
• Cyclones are associated with high temperatures of over 27° C. These warm up the air resulting into heavy convective instability and formation of dense cumulonimbus clouds.
• Sudden appearance of calm, clear, and dry conditions with the advance of the eye and then violent conditions
• They are characterized by high humidity and temperatures.

Cyclones affect human activities and coastal areas in tile following ways;

• -In India & New Orleans & Bangladesh Violent winds blow up settlements, ships and most of the infrastructure. This leads to loss of shelter, total power blackout due to destruction of electricity lines and destruction of the transport infrastructure.
• Violent winds lead to loss of livestock, crops and humans are killed by flying debris or suffocated to death by the gusty winds. Breathing is very hard under such winds.
• Cyclones result into flooding of coastal islands and towns. In U.SA, New Orleans and Florida are usually flooded. In India coastal towns flood and slums are hit most.
• Cyclones are normally followed by an outbreak of water borne diseases liked diarrhea, cholera etc. this is a result of floods. Such diseases are common in India, Bangladesh and New Orleans in USA where the Katarina cyclone caused havoc in 2010
• Cyclones lead to food shortages which may result into famine. This is a result of the destruction of crops, animals and the entire social and economic infrastructure.
• Disturbance of shipping and aviation travel industry because of the gusty winds, torrential rains and poor visibility.
• Land degradation due to massive erosion and mass wasting resulting from torrential rains especially near the coast.
• Salination of coastal lands because of the periodic sea incursions thus affecting crop cultivation.
• They destroy vegetation by uprooting trees and braking branches thus destroying leisure parks,along beaches