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Social sciences: geography

Grade 7

Natural hazards

Module 3

Tropical cyclones

1. Tropical Cyclones

  • The occurrence and cause of tropical cyclones

No weather phenomenon is more terrifying and destructive than a tropical storm. In America such storms are called hurricanes, in Asia typhoons, in South Africa tropical cyclones and in Australia Willie-willies.

Features of tropical cyclones

They develop over the warm, tropical oceans near the equator. The warm, tropical seawater heats the air that rests upon it up to temperatures of ± 27°C. The high degree of evaporation makes the air very humid. That is why the tropical easterly winds are chiefly characterized by the fact that they are hot and humid. This causes the air above the oceans to rise swiftly, resulting in extremely low pressure. The convection currents start spiralling at an ever increasing speed. The air rises more and more, and condensation and cumulus and cumulonimbus clouds are formed. The rotation of the earth on its own axis causes the cloud masses to circle, which creates a gigantic, swirling storm.

In the centre of this cyclone there is an eye of moist, cloudless weather that can be about 35-50 km wide. Here atmospheric pressure readings are less than 1 000 hPa. Directly around it storm winds rage at 120-280 km/h. Stormy weather can occur up to 200 km from the eye, and these storms can continue for a few hours or even for a number of days. They move forward slowly (15-20 km/h) and start to subside as soon as they reach the land surface or cooler water. Great destruction, heavy downpours and tidal waves occur for a number of days along the coastal areas of the affected countries.

Traditionally cyclones were named after women because of their capricious nature. Nowadays they are sometimes also named after men. The relentless tropical cyclone “Hugo” that hit the east coast of America in 1989 is one such example.

Such a storm would be indicated on a weather chart by round isobars that are closely positioned around the eye.

Synoptic weather chart

2. The effect (consequences) of tropical cyclones on peoples’ lives and their socio-economic activities

South Africa does not often experience the utter ferocity of a tropical storm. However, when it does occur, it causes just as much destruction as in other parts of the world.

The worst cyclone that has ever been recorded along the South African coast was the tropical cyclone Demoina. On 25 January 1984 Demoina veered inland from a position near Maputo. The following two days it caused violent storms, high winds and a great deal of rain over parts of South Africa. At some places as much as 540 mm was recorded in a period of 24 hours. In Northern Natal rivers burst their banks. Villages near rivers were totally destroyed, bridges were washed away and crops on the banks of the rivers were destroyed. Damage to sugar plantations was estimated at R150 000 000. At least 200 people lost their lives. It was difficult to carry out rescue operations because most of the bridges and roads in the affected areas had been washed away. The gale force winds made conditions extremely hazardous for helicopters. Bodies of victims, and even crocodiles, were washed into the sea. The death toll rose even higher as a result of waterborne diseases and famine.

Questions & Answers

Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Geography grade 7. OpenStax CNX. Sep 09, 2009 Download for free at http://cnx.org/content/col11021/1.1
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