Transcript Slide 1

NASA
1
Hurricane
NASA
2
NOAA
Cyclone
3
Typhoon
Tropical Cyclones
17/07/2015
Learning Objectives:
•What conditions lead to
tropical cyclones?
•In what way do they represent
a hazard to people?
What is a tropical cyclone?
A tropical cyclone is a low pressure system
over tropical or sub-tropical waters, with
organised convection (i.e. thunderstorm
activity) and winds at low levels circulating
either anti-clockwise (in the N.hemisphere) or
clockwise (S.hemisphere). It has an average
diameter of ~500km and height ~15km.
Where does a tropical cyclone form?
In the tropics!
What ingredients are required for their
formation?
•Warm water (>26.5oC)to a depth of at least 50m.
•An existing atmospheric disturbance (e.g. a weak
low pressure system)
•Must be at least 500km (300miles) north or south of
the equator so that the Coriolis force is strong
enough to aid their development.
•Small wind shear (only small change in wind speed
throughout the atmosphere) so the developing
system does not get ‘torn apart’.
NOAA
4
World map showing the track of all known tropical
cyclones. Note how none have formed in close
proximity to the equator. Add the names of tropical
cyclones in each region to your world map.
Naming conventions of tropical cyclones
for world regions
"hurricane" (the North Atlantic Ocean, the Northeast
Pacific Ocean east of the dateline, or the South Pacific
Ocean east of 160E)
"typhoon" (the Northwest Pacific Ocean west of the
dateline)
"severe tropical cyclone" (the Southwest Pacific Ocean
west of 160E or Southeast Indian Ocean east of 90E)
"severe cyclonic storm" (the North Indian Ocean)
"tropical cyclone" (the Southwest Indian Ocean)
NOAA
4
Tropical
cyclone
Severe
cyclonic
storm
Severe
tropical
cyclone
Hurricanes
Typhoons
Worldwide Tropical Cyclone Statistics
•14.9 hurricanes per year 1851-2006 average
•16.9 typhoons per year 1959-2005 average
Date of storm formation
in the Atlantic.
Named systems – Yellow
Hurricanes – Green
Category 3 or greater - Red
6
5
Tropical Cyclone Formation
(Tropical Cyclogenesis)
NASA
This satellite image clearly
shows the intertropical
convergence zone (ITCZ).
However it is broken into
discrete clusters of
thunderstorms. These are
known as ‘waves’.
Forecasters watch these
areas for signs of tropical
cyclogenesis.
7
NASA
ITCZ
Wave disturbance
Tropical cyclones originate
from a humble
NOAA - 8
thunderstorm!
These require converging air
at the surface i.e. a low
pressure system such as a
wave on the ITCZ. These have
anticlockwise winds (in the
N.hemisphere) and so only
form 500km either side of
the equator (between 5o and Converging air in a low
20o) where the Coriolis ‘force’
pressure forming
is strong enough.
thunderstorms
Upper, cold low pressure
Warm, humid air
Warm sea
If a cold upper-level
trough from midlatitudes moves into
the area of
thunderstorm
development then
the air becomes
convectively very
unstable and the
thunderstorms will
start to grow very
large.
As latent heat is released by the condensing water vapour,
the cold air aloft warms and increases in pressure.
Diverging (moving
apart) air aloft
High
pressure
Low
pressure
NWS - 9
Latent heat experiment
Bring 50ml of water to the boil. Time how long
it takes for all of this water to evaporate.
The total amount of energy supplied to the
water can be calculated from:
Energy = Time x 9800J/s
The latent heat of water can be found from:
L=Q/m
Where Q = Energy supplied and m= mass of
water used in kg.
Latent heat experiment
You should find L=2.3million Joules/kg
This tells you how much heat energy is
released when 1kg of water vapour condenses
into liquid water in a tropical storm.
On average 1,000,000,000kg of water
condense per second in a tropical cyclone.
Calculate how much energy is released per
second in a tropical cyclone.
Answer: 2.3x1015 J/s
This amount of
energy is the
equivalent of a 10
megaton nuclear
bomb exploding
every 20 minutes!
A 10.4 Megaton nuclear bomb test
US Department of Energy - 10
The diverging air aloft
‘sucks’ air up from the
surface and with
continued convection
causes the surface low
pressure to drop further.
Surface winds now
increase and begin to
spiral inwards. This make
the sea rougher which
makes the winds turn
further to the centre of
the developing storm.
L
Blue arrows – Pressure gradient
force (pgf )
Red arrows - Coriolis force
Black arrows – Direction of wind
As the surface friction increases, the
wind slows and so the Coriolis ‘force’
decreases. The pgf remains constant and
so the winds spiral into the centre of the
surface low.
The feedback mechanism:
-Air now reaching centre is warm and moisture laden
after travelling over choppy warm seas.
-This adds extra energy in the form of latent heat to the
thunderstorms, increasing their rate of growth
-The surface pressure drops further
-Surface winds increase
-Sea becomes more choppy
-Extra warmth and moisture transferred to the air
-And so on.
-When 35-64 knot wind speed is reached we call it a
tropical storm and when it increases to 65 knots we call it
a tropical cyclone.
Task:
Rearrange the statements to show the
process of tropical cyclogenesis.
Or
Rearrange the pictures to show the stages of
tropical cyclogenesis. Label them to provide
an explanation of the processes involved.
Eye of storm = Calm light winds
H
>15km
L
~500km
Eye – Centre of storm. Calm conditions. Surrounded by
most violent winds up to ~200mph under the eye wall
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NASA - 1
Hurricane Katrina
Hurricane Luis eye video satellite image
Picture taken by the NOAA Hurricane hunter aircraft
which monitors hurricanes which are threatening the US coast.
This growth will continue until:
•Moisture is cut off – i.e. Cyclone moves over
land
•Heat is cut off – i.e. Cyclone moves too far
north or south
•Wind shear (wind strength increasing with
height) increases – This tears the cyclone
apart – Common near Hawaii. Video
•Cyclone becomes ‘full’ of thunderstorms so
latent heat release is limited.
NASA - 2
1.) Storm surge (up to 5m) due to a) low pressure causing
local rises in sea levels and b) wind pushing water along.
90% of deaths in tropical cyclones are due to flooding.
NASA - 12
Video
Relative effects of
pressure surge and
wind-driven surge.
Wikipedia - 13
2.) Wind damage
Video
of
flying
debris
3.) Flying debris
4.) Damage to infrastructure e.g. Roads and
electricity supplies.
FEMA News Photo - 14
Damage
from
Hurricane
Katrina
Social
•Deaths & injuries
•Disease
•Disruption to all events
e.g. School, work, sport
•Ensuing or deepened poverty
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FEMA News Photo - Davie, Florida 2005
Economic
•Cleanup bill
•Damage to buildings & infrastructure
•Loss of businesses
•Loss of tourism
Environmental
•Destruction of
habitats
•Sewage leaks
•Chemical leaks
New Orleans, Louisiana 2005
US Coast Guard - 16
US Coast Guard
Hurricanes are
rated on the
Saffir Simpson
Scale – Link to
official scale
Animation with
interactive SaffirSimpson Scale
17
Hurricane Andrew: Video
•24th August 1992
•Bahamas & Florida
•Category 5
•Max average 1 min wind
speed = 175mph
NOAA - 18
•Lowest pressure = 922mbar
•Storm surge of 5.2m
•67 deaths
•$41.1 billion (adjusted to 2010 rates)
•Over 1.1 million people evacuated and 1500 troops
deployed to prevent looting.
Hurricane Mitch:
Video
•29th October 1998
•Honduras, Nicaragua, Mexico,
NOAA - 19
Florida(flooding also in Central America)
•Category 5
•Max average 1 min wind
speed = 180mph
•Lowest pressure = 905mbar
•Storm surge of 3.7m in Honduras
•11,000 deaths mainly in Central America due to flooding
and mudslides – Up to 1500mm (5 feet) of rain fell!
•$8 billion (adjusted to 2010 rates)
•Honduras evacuated 45,00 people and put armed forces
on standby. 100,000 later evacuated.
Hurricane Katrina: Video
•29th August 2005
•Bahamas, Florida Louisiana
NOAA - 20
•Category 5 (3 at landfall in Louisiana)
•Max average 1 min wind
speed = 175mph
•Lowest pressure = 902mbar
•Storm surge of 4.3m in Louisiana
•1836 deaths
•$90.1 billion (adjusted to 2010 rates)
•State of emergency declared two days in advance.
Unprecedented text used in weather statement to convey
likely devastation of storm. 1.2 million people ordered to
leave homes.
Super Typhoon Saomai:
•10th August 2006
Video
•Zhejiang Province, China
•Category 5 (4 at landfall)
•Max average 1 min wind
speed = 160mph
NOAA - 21
•Lowest pressure = 925mbar
•Storm surge of 4.0m
•458 deaths
•$2.7 billion (adjusted to 2010 rates)
•50,000 houses destroyed; 380 km2 of farmland flooded.
•1.6 million people evacuated. 20,000 soldiers deployed to
help in the cleanup and rescue efforts.
NASA
Cyclone Larry:
Video
•20th March 2006
•Queensland, Australia.
•Category 5 (4 at landfall)
•Max average 1 min wind
speed = 135mph
•Lowest pressure = 940mbar
•Storm surge of 2.3m
•1 indirect death
•$920 million (adjusted to 2010 rates)
•Most banana crops destroyed, many houses in the direct
path were damaged (including 99% in Silkwood).
Homework – Due
Research two tropical cyclones in different parts of the
world, gathering data on:
•Meteorological statistics
•Preparations
•Impacts
•Responses to the cyclone including rebuilding plans and progress.
Extension
-Discuss how future development planning could
incorporate tropical storm preparedness designs.
- OR argue whether we should continue building in these
areas at all.
Role play! A major hurricane is heading towards the
southern coast of the US where you live. Act as if you
were:
-Meteorologist advising authorities
-Governor of state
-Emergency services on the ground
-Homeowner
-Business owner
-Storm chaser!
Imagine the views you would have as each of these
characters and how you would argue your case.
Sources:
1) NOAA - http://www.katrina.noaa.gov/satellite/images/katrina08-29-2005-1345z2.jpg
2) Image Science and Analysis Laboratory, NASA-Johnson Space
Center. "The Gateway to Astronaut Photography of Earth”.
http://eol.jsc.nasa.gov/sseop/images/EO/highres/ISS008/ISS008
-E-19646.JPG
3) NOAA - http://www.nnvl.noaa.gov/members/images/109687.jpg
4) Wikipedia Commons http://en.wikipedia.org/wiki/File:Global_tropical_cyclone_tracks
-edit2.jpg
5) NHC NOAA - http://www.nhc.noaa.gov/gifs/peakofseason.gif
6) NHC NOAA - http://www.nhc.noaa.gov/gifs/atlhist_lowres.gif
7) NASA http://disc.sci.gsfc.nasa.gov/oceancolor/additional/sciencefocus/ocean-color/science_focus.shtml/convergence.shtml
Sources:
8) NWS - http://www.srh.weather.gov/jetstream/tstorms/life.htm
9) NWS http://www.srh.noaa.gov/jetstream//tropics/tc_structure.htm
10) US Department of Energy http://www.cfo.doe.gov/me70/manhattan/early_bomb_design.h
tm
11) NOAA http://www.srh.noaa.gov/lzk/imgviewer2.php?pic=katrinaeye08
2805
12) NASA http://earthobservatory.nasa.gov/Features/Hurricanes/Images/s
torm_surge.gif
13) Emmanuel.boutet – Wikipedia http://en.wikipedia.org/wiki/File:Surge-en.svg
Sources:
14) FEMA News Photo http://www.photolibrary.fema.gov/photodata/original/14801.jpg
15) FEMA News Photo http://www.photolibrary.fema.gov/photodata/original/14365.jpg
16) US Coast Guard http://www.uscg.mil/history/katrina/katrinaoralhistoryindex.as
p
17) Wikipedia
http://en.wikipedia.org/wiki/Saffir%E2%80%93Simpson_Hurric
ane_Scale
18) NOAA- http://www.publicaffairs.noaa.gov/photos/1992andy1.gif
19) NOAA - http://www.ncdc.noaa.gov/img/olimages/hurr-mitch19981027-n15.gif
Sources:
20) NOAA - http://www.katrina.noaa.gov/satellite/images/katrina08-29-2005-1315z2.jpg
21) NOAA - http://www.nnvl.noaa.gov/cgibin/index.cgi?page=items&ser=111116
22) NASA http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=1
6268&oldid=13421