Transcript Lesson 1 - The Student Room

Lesson 16
How do Tropical Revolving
Storms Form?
We need to understand how tropical
revolving storms are created, their impacts
and know how people respond to them.
We should also take into account the effects
of global warming on such events.
What drives a Tropical Storm?
Cold polar air
moves towards
the warm
equator.
Hot tropical air
moves towards
the cold poles.
The planet is not evenly heated.
At A the heating is more direct =
intense.
Whereas at B it is spread over a
larger surface area = less intense.
What causes wind?
This uneven heating causes air to move
around the planet, trying to even out the
temperature.
 Air moving
around the
planet causes
our wind, which
generally
follows a known
pattern.

Tropical storms
form between
5ºand 20º North
& South of the
equator.
They need warm
water ~ above
27ºc – hence their
location.
As the Earth rotates, this provides the ‘spin’
needed to start the tropical storm on its
journey across the Atlantic towards America.
17%
11%
8%
11%
33%
20%
Tropical revolving storms occur all around
the world, but are called different names.
Warm Oceans
The ‘food’ of a tropical
storm is the warm moist
water found near the
equator. The air here is
under LOW pressure, which
means it can lift easily.
This lifting encourages the
air to cool and condense, as
it does latent heat is
released. This is the name
given to energy produced
when a substance changes
state ie vapour to a liquid.
Here is a check list
of what is needed
for a tropical
revolving storm
to grow.
Once the storm
has developed
it can grow 400
miles wide.
A storm can travel anywhere from 15 to 40mph
Here is a 3D
image of a
Tropical
revolving
storm. Notice
the lower
level winds
being drawn in
and spiralling
counter
clockwise.
The lines ‘isobars’ get closer together,
indicating faster flowing air.
Launch the hyper link
How Hurricanes form
Tropical Storm / Hurricane Key Facts
Hurricanes are located in the low-pressure belt near the equator as the
sun heats the oceans to a critical temperature of 27C.
The oceans heat up all through the summer making their warmest
temperatures in the Autumn (specific heat capacity); this is Hurricane
season in the Atlantic.
The hurricane starts as a tropical depression, gaining more and more
energy from the warm ocean as it crosses the Atlantic. The circulation of
the depression gets tighter (isobars are closer together) and the wind
speed increases into a tropical storm.
The wind speeds continue to increase, becoming a category 1 up to
category 5 for the most violent storm. As the hurricane makes landfall
damage is done by the winds and rain and an advancing storm surge,
which raise sea level by 5m+ in some cases.
The hurricane quickly looses its energy as it crosses the cooler land, as
the energy supply has been cut off. The hurricane dies.
Sometimes remnants of hurricanes are brought across back across the
Atlantic at the mid latitudes giving us very strong depressions in the UK.
How are they measured?
Although developed in the USA, the Saffir-Simpson scale is
used to grade tropical storm wind strength in many parts of
the world.
Category
Tropical storm
Wind Speed Wind Speed
km/hr
Mph
0-62
Storm
Surge m
0
Tropical depression
63-117
0-0.9
1
119-153
74-95
1.2-1.5
2
154-177
96-110
1.8-2.4
3
178-209
111-130
2.7-3.7
4
210-249
131-155
4.0-5.5
5
>250
>155
<5.5
Problems with the Saffri Simpson?
Q… Using wind speed and storm surge levels
– what problems could you encounter?
http://www.nhc.noaa.gov/aboutsshs.shtml
A tropical storm has many friends!
Other phenomena which can be just as damaging than the wind frequently
accompany tropical storms:
high seas - large waves of up to 15 metres high are caused by the strong
winds and are hazardous to shipping;
storm surge - a surge of water of up to several metres can cause extensive
flooding and damage in coastal regions;
heavy rain - the tropical cyclone can pick up two billion tons of moisture
per day and release it as rain. This also leads to extensive flooding - often
well inland from where the tropical revolving storm hit the coast;
tornadoes - tropical cyclones sometimes spawn many tornadoes as they hit
land which can cause small areas of extreme wind damage. These
phenomena can cause major destruction, especially when the tropical
cyclone's path takes it over land. However, a path over land also causes the
destruction of the tropical cyclone itself. As it moves over land, its energy
source is depleted and friction across the land surface distorts the air flow.
This leads to the eye filling with cloud and the tropical cyclone dies.
3D model of a Tropical Storm
Create your own 3D
model – remember to
add a key!
Homework
AQA A2 book Pg 60-63 Read and make notes
Visit these web sites and read around the topic – what
else can you add to your notes about tropical
revolving storm formation?
Waugh Pg 235 & Nagle Pg 421+ has extra reading,
(pay particular attention to Places 30 for Stretch &
Challenge!)
http://www.bbc.co.uk/weather/features/understand
ing/hurricane_cycle.shtml
http://www.metoffice.gov.uk/weather/tropicalcyclo
ne/facts.html
http://www.nhc.noaa.gov/aboutsshs.shtml