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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

Need help solving this problem (2/7)^-2
Simone Reply
what is the coefficient of -4×
Mehri Reply
the operation * is x * y =x + y/ 1+(x × y) show if the operation is commutative if x × y is not equal to -1
Alfred Reply
An investment account was opened with an initial deposit of $9,600 and earns 7.4% interest, compounded continuously. How much will the account be worth after 15 years?
Kala Reply
lim x to infinity e^1-e^-1/log(1+x)
given eccentricity and a point find the equiation
Moses Reply
12, 17, 22.... 25th term
Alexandra Reply
12, 17, 22.... 25th term
College algebra is really hard?
Shirleen Reply
Absolutely, for me. My problems with math started in First grade...involving a nun Sister Anastasia, bad vision, talking & getting expelled from Catholic school. When it comes to math I just can't focus and all I can hear is our family silverware banging and clanging on the pink Formica table.
I'm 13 and I understand it great
I am 1 year old but I can do it! 1+1=2 proof very hard for me though.
Not really they are just easy concepts which can be understood if you have great basics. I am 14 I understood them easily.
find the 15th term of the geometric sequince whose first is 18 and last term of 387
Jerwin Reply
I know this work
The given of f(x=x-2. then what is the value of this f(3) 5f(x+1)
virgelyn Reply
hmm well what is the answer
If f(x) = x-2 then, f(3) when 5f(x+1) 5((3-2)+1) 5(1+1) 5(2) 10
how do they get the third part x = (32)5/4
kinnecy Reply
make 5/4 into a mixed number, make that a decimal, and then multiply 32 by the decimal 5/4 turns out to be
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
okay, so you have 6 raised to the power of 2. what is that part of your answer
I don't understand what the A with approx sign and the boxed x mean
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
I'm not sure why it wrote it the other way
I got X =-6
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
oops. ignore that.
so you not have an equal sign anywhere in the original equation?
is it a question of log
I rally confuse this number And equations too I need exactly help
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Commplementary angles
Idrissa Reply
im all ears I need to learn
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greetings from Iran
salut. from Algeria
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
A soccer field is a rectangle 130 meters wide and 110 meters long. The coach asks players to run from one corner to the other corner diagonally across. What is that distance, to the nearest tenths place.
Kimberly Reply
Jeannette has $5 and $10 bills in her wallet. The number of fives is three more than six times the number of tens. Let t represent the number of tens. Write an expression for the number of fives.
August Reply
What is the expressiin for seven less than four times the number of nickels
Leonardo Reply
How do i figure this problem out.
how do you translate this in Algebraic Expressions
linda Reply
why surface tension is zero at critical temperature
I think if critical temperature denote high temperature then a liquid stats boils that time the water stats to evaporate so some moles of h2o to up and due to high temp the bonding break they have low density so it can be a reason
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris 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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