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You'll
need to access the content at the following internet location : Modelling
Tropical Cyclones.
Photocopy maps of Queensland,
The Northern Territory and/or Western Australia for use with the task
on making a cyclone out of plasticine. Choose maps that have a scale
and will result in plasticine cyclones that will be large enough to
work with. A small map has been provided on the student worksheet.
Print
off the student's worksheet and photocopy
one for each student.
Ask the students to carry
out the activity from the worksheet then go over their results at the
end of the class. Please note cyclone rotation is reversed in the northern
hemisphere.
Solutions
- Students
should make a model similar in design to the animation. They need
to refer to the map's scale to ensure that their plasticine model
is of the correct size. Highlight the enormous size of a cyclone and
the fact that the eye is clear allowing them to see the map below
through it. The map scale should only be used for the diameter of
the cyclone not the height. As with the animation most cyclone diagrams
use a different scale for the height to exaggerate the structure of
the cyclone.
- They should
draw their cyclone with the eye labelled. Ask a student to demonstrate
how the top part of the cyclone turns in the opposite direction to
the bottom. This is due to winds in the upper levels of the atmosphere
moving in the opposite direction to those in the lower levels (this
is a typical condition but not always the case). They should turn
the bottom part in a clockwise direction (for southern hemisphere
tropical cyclones only).
- Figure
1 shows the wind speed being high around the eye of the cyclone and
very low in the eye itself.
- Students
should choose a coastal city on their map and write a short piece
about what they would observe as the cyclone passes. They should mention
that the wind speed will increase as the eye approaches. They should
describe some of the devastation caused by the strong winds and heavy
rain. The wind speed drops dramatically when they are in the eye and
then the wind comes from the opposite direction and increases in speed
as the eye passes. They will observe a lot of rain and cloud until
they are in the eye where it is clear and still. If they choose a
coastal area they may mention a rise in the sea level i.e. a storm
surge. This is a large and sudden rise in sea level which occurs close
to the eye of the storm near the region of maximum onshore winds which
is just to the left (in the southern Hemisphere) of the cyclone centre
in the direction of motion as it crosses the coast. The surge is produced
by the combined effects of the sudden reduction in atmospheric pressure
and the very strong winds piling up the sea water. The worst surges
occur when the cyclones coastal crossing time coincides with a very
high tide. More than 140,000 people were drowned in Bangladesh in
1991 through the flooding of coastal communities by a storm surge
generated by a tropical cyclone.
- Satellites
are used to detect and track cyclones. Geostationary satellites take
photos of the earth at hourly intervals. These help us to see if a
cyclone is forming and allow us to track its movements. Warnings can
then be given to areas that seem to be in its path.
- They are
similar. The Bureau's logo is a stylised representation of the southern
hemispere tropical cyclone, with winds spiralling clockwise and inwards
to the calm, cloudless 'eye' at its low pressure centre. Why the Bureau
chose that symbol is arguable and can be related to the Bureau's Service
Charter.
A good response would be that it relates to the Bureau's role of 'helping
people make better-informed decisions affecting their lives and their
community and business activities, on a daily basis and in their long-term
planning, and especially in dangerous or life-threatening weather
situations'.
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