Download storm surge

WIND, MONSOONS AND
CYCLONES
CYCLONES AND
STORM SURGES
 See Bos 157C: what is the most dangerous month for typhoons in
Japan?
 Cyclones = tr… storms which start above warm seawater (> 27 C)
 Haiyan:windspeed .>300 km/hr (34 mln Euro collected in Neth):
Saffir Simpson Scale = category 1 ,2,3,4,5 ?
 Storm surge and tides (tsunami = tidal wave)
Potentially, the most destructive phenomenon associated with
tropical cyclones that make landfall is the storm surge. Storm
surge is a raised dome of water about 60 to 80 km across and
typically about 2 to 5 m higher than the normal tide level. If the
surge occurs at the same time as a high tide then the area
inundated (flooded) can be quite extensive, particularly along
low -lying coastlines.
See Bos 157C ; what proportion of the coastline of Japan is
threatened by tsunamis ¼ - 2/4 -3/4 4/4
TROPICAL CYCLONES
 Tropical cyclones move with the tradewinds to the west (finish
North/NE) (see sketch)
 Tropical cyclones develop in Tropical Area above seawater 27C
 Develop in the summer-autumn period of each hemisphere
so: ( 21 june till 21 dec in Northern Hemisphere)
or (21 ….. till 21 ……… in Southern Hemishpere)
 Storm develops because sea water starts to evaporate and
this evaporated air starts to rise: the rising air cools and
condensates -> rain. As a result of this proces energy is
released and the air can rise still higher.
 At the surface of the water a very deep low pressure centre
evolves (920 HPA air pressure (usu.1010): result: more air will
be sucked into the this system and the storm will develop into
a superstorm
TROPICAL CYCLONES
 Tropical cyclones use warm, moist air as fuel . That is why they form
only over warm ocean waters near the equator. The warm, moist air
over the ocean rises rapidly upward from near the sur face and becomes
saturated ( verzadigd) with evaporated moisture ( vocht) . This means
that there is less air lef t at the sur face (i.e. low pressure). Air from
surrounding areas with higher air pressure pushes in to the low
pressure area to tr y to equalise the pressure . Then that “new” air
becomes warm and moist and rises, too. As the warm air continues to
rise, the surrounding air swirls in to take its place.
 Trade winds ( blow to the Equator ) cause the moist air to spin inwards.
As the warmed, moist air rises and cools of f , the water in the air forms
towering cumulonimbus ( bloemkoolwolken) thunderclouds (because
there is a huge amount of condensation). The whole system spins and
grows, fed by the ocean’s heat and water evaporating from the sur face .
The diagram below shows a cross section system of clouds and wind
through a tropical storm.
T YPHOONS
TROPICAL CYCLONE
STORMS
 As the storm system spins faster and faster, an eye forms in
the centre.
 It is very calm and clear in the eye, with very low air pressure.
 Higher pressure air from above flows down into the eye
SAFFIR SIMPSON
TROPICAL CYCLONES
 Tropical cyclones usually weaken when they make landfall
(i.e. hit the land) because they are no longer being fed by the
energy from the warm ocean waters. In the northern
hemisphere they track (i.e. move) westwards due to the
Coriolis ef fect.
 The cyclone season starts at the end of het summer and in
autumn. At that time the land is already cooling down more
than the surrounding sea. This slows down also the power of
the cyclones when they make landfall
MAIN WIND SYSTEMS
WEBLINKS
 Useful weblinks:
 BBC animation - the formation of a hurricane
 NASA animated guide to the development and structure of
tropical storms
 Make a tropical storm - simulator
 Investigate how winds work together to determine where a
hurricane will strike - simulator
 BBC Bitesize revision notes about the formation of tropical
storms

 http://worldlywise.pbworks.com/w/page/25349490/Unit%202%
20Section%20C%20%20Causes%20and%20effects%20of%20tropical%20storms%20
and%20responses%20to%20them (also animations of tsunamis
and earhquakes etc!)