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What is the name of the meteorological phenomenon that means the same as all of these?
NASA Hurricane 1 NASA NOAA 3 Typhoon Cyclone 2
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Tropical Cyclones 21/09/2018 Learning Objectives: What conditions lead to tropical cyclones? In what way do they represent a hazard to people?
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What are tropical cyclones? Where do they form?
What ingredients are required for their formation?
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What is a tropical cyclone? Where does a tropical cyclone form?
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!
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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’.
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What is the difference between a typhoon, hurricane and a cyclone?
The region in which they form
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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.
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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)
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Severe tropical cyclone Hurricanes Severe cyclonic storm
NOAA 4 Severe tropical cyclone Hurricanes Severe cyclonic storm Tropical cyclone Typhoons
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Date of storm formation in the Atlantic.
Worldwide Tropical Cyclone Statistics 14.9 hurricanes per year average 16.9 typhoons per year average Date of storm formation in the Atlantic. Named systems – Yellow Hurricanes – Green Category 3 or greater - Red 6 5
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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
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Tropical cyclones originate from a humble 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 20o) where the Coriolis ‘force’ is strong enough. NOAA - 8 Converging air in a low pressure forming thunderstorms
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If a cold upper-level trough from mid-latitudes moves into the area of thunderstorm development then the air becomes convectively very unstable and the thunderstorms will start to grow very large. Upper, cold low pressure Warm, humid air Warm sea
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Diverging (moving apart) air aloft
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
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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.
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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.
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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
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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.
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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 knot wind speed is reached we call it a tropical storm and when it increases to 65 knots we call it a tropical cyclone.
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Rearrange the statements to show the process of tropical cyclogenesis.
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.
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Eye of storm = Calm light winds
>15km L ~500km
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Eye – Centre of storm. Calm conditions
Eye – Centre of storm. Calm conditions. Surrounded by most violent winds up to ~200mph under the eye wall 11 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.
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What factors stop the tropical growing to the size of the Earth!?
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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.
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How do tropical cyclones pose a danger to people?
NASA - 2
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90% of deaths in tropical cyclones are due to flooding.
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
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Video of flying debris 2.) Wind damage 3.) Flying debris
4.) Damage to infrastructure e.g. Roads and electricity supplies. Video of flying debris FEMA News Photo - 14 Damage from Hurricane Katrina
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What are the social, economic and environmental issues associated with tropical cyclones?
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Disruption to all events e.g. School, work, sport
Social Deaths & injuries Disease Disruption to all events e.g. School, work, sport Ensuing or deepened poverty Economic Cleanup bill Damage to buildings & infrastructure Loss of businesses Loss of tourism 15 FEMA News Photo - Davie, Florida 2005
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Destruction of habitats Sewage leaks Chemical leaks
New Orleans, Louisiana 2005 US Coast Guard - 16 Environmental Destruction of habitats Sewage leaks Chemical leaks US Coast Guard
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Hurricanes are rated on the Saffir Simpson Scale – Link to official scale
Animation with interactive Saffir-Simpson Scale 17
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Case Studies Hurricane Andrew: 24th August 1992 Bahamas & Florida
Category 5 Max average 1 min wind speed = 175mph 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. Video NOAA - 18
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Case Studies Hurricane Mitch: 29th October 1998
Honduras, Nicaragua, Mexico, 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. Video NOAA - 19
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Case Studies Hurricane Katrina: 29th August 2005
Bahamas, Florida Louisiana 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. Video NOAA - 20
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Case Studies Super Typhoon Saomai: 10th August 2006
Zhejiang Province, China Category 5 (4 at landfall) Max average 1 min wind speed = 160mph 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. Video NOAA - 21
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Case Studies Cyclone Larry: 20th March 2006 Queensland, Australia.
NASA Cyclone Larry: 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). Video
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Meteorological statistics Preparations Impacts
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.
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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.
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Sources: NOAA - Image Science and Analysis Laboratory, NASA-Johnson Space Center. "The Gateway to Astronaut Photography of Earth”. NOAA - Wikipedia Commons - NHC NOAA - NHC NOAA - NASA -
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Sources: NWS - NWS - US Department of Energy - NOAA - NASA - Emmanuel.boutet – Wikipedia -
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Sources: FEMA News Photo - FEMA News Photo - US Coast Guard - Wikipedia NOAA- NOAA -
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Sources: NOAA - NOAA - NASA -
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