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The Physical Characteristics of Tropical Cyclones Case Study: The 1970 Bhola Cyclone

Tropical cyclone by Martin

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The slides teach us about tropical cyclones

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The Physical Characteristics of Tropical Cyclones

Case Study: The 1970 Bhola Cyclone

Tropical Cyclones

A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms

Tropical Cyclones: Grounds of rotating, low-pressure storms that form around the equator.

Cyclones, Hurricanes, Typhoons Named according to

region where they develops

Cyclones – Develop over the Indian Ocean on worm waters

Hurricanes - Develop over Atlantic and eastern Pacific Oceans

Typhoons – Develop over western Pacific Oceans

All produce similar effects

Typhoon Odessa, Philippines

Eye

Fact.

The strongest of these cyclones storms are known in the US and other parts of the Atlantic ocean

Developmental Stages

Progression: depression storm cyclone

Classified according to wind speeds

Tropical Depression - less than 39 m/h

Tropical Storm - between 39 m/h and 73 m/h

Tropical Cyclone - at least 74 m/h

Tropical Cyclones Introduction

Tropical cyclones are intense, rotating, low-pressure storms

Develop over warm, tropical oceans

Produce strong winds and heavy rainfall

Can lead to immense flooding

Destructive Winds

Formation of tropical cyclones

Tropical Cyclones require to basic conditions to form: an abundant supply of very warm ocean water and some sort of disturbance to lift warm air and keep it rising.

Formation of Tropical Cyclones

Warm water generates formation of tropical cyclones

Ocean temperatures must be at least 26.5°C which is worm

Over warm oceans moist, humid air (water vapour)

Warm air moves along the surface

This air converges and rises rapidly

Intense rising of air forms low pressure systems

Formation of Tropical Cyclones

As air rises, it cools, becomes saturated and condenses

Water vapour condenses into liquid droplets

Formation of thunderclouds

Condensation releases heat stored in water vapour

This latent heat warms the atmosphere

Air becomes lighter causing strong updrafts

Formation of Tropical Cyclones

Air expands and diverges at higher levels

Occurs only where wind speed/direction remain constant (no wind shear)

Air moves in at surface taking the place of rising air

This intensifies convergence

Creates wind and increases rising movement

Builds and progresses into a mature cyclone

Coriolis Effect

Spinning of earth on its axis produces wind deflections (Coriolis Effect)

Causes rising air to spiral around center (core)

Spirals with great force

Winds are now rotating, rising and moving in to fill spaces

Wind speeds increase and cyclone grows

Conditions

These conditions exist in all tropical oceans except the south Atlantic ocean and the pacific, west of the South American coast ocean waters in these areas are somewhat cooler.

Coriolis Effect

Northern hemisphere winds are blowing counter-clockwise around center core

Southern hemisphere winds are blowing clockwise around center core

The Eye, Eyewall, Rainbands

The Eye - the clear, calm center of storm

Cool air descends into this center (downdrafts)

Eyewall – ring of thunderstorms close to eye

Eyewall produces the most devastating winds

Rainbands – curved groups of clouds and thunderstorms

Rainbands travel away from eye in a spiral motion

Storm Surges

Occur when tropical cyclones reach land

Storm surge – raised swell of water

60 to 80 km across

Around 2 to 5 meters higher than normal tides

Created by heavy winds and cause flooding

Locations of Tropical Cyclones

Between 10 to 30° North and South of equator

Within the tropic of Cancer and Capricorn Poleward side of the Intertropical Convergence Zone

Zone of low pressure (ITCZ)

Coriolis effect greatly reduced at equator No tropical cyclones occur at equator

Tropical Cyclone Appearances

ITCZ

Tropical Cyclone Categories

Case Study: The 1970 Bhola Cyclone

Storm Survivors

The 1970 Bhola Cyclone

November 12, 1970

The deadliest tropical cyclone recorded Developed over Bay of Bengal

Gathered speed as it moved northward

Devastated East Pakistan (Bangladesh) and West Bengal of India

Storm Path

India

Bay of Bengal

The Bhola Cyclone Characteristics

Wind speeds reached 115 m/h Strength of a category 3 hurricane 33 foot high storm surge Massive storm surge caused flooding and fatalities

Bhola Cyclone on November 11, 1970

The Bhola Cyclone - Damage

Storm surge:

• Flooded low-lying islands

• Wiped out crops

• Destroyed whole villages

• Demolished 85% of homes in the area Estimated damage at 86.4 million dollars 300,000 - 500,000 people were killed

Great Bhola Cyclone

Mid-latitude Storms

Unlike mid latitude storms that derive their energy from the contrast between warm and cold air masses. Tropical Cyclones oceans as water evaporates from the ocean surface.

Ocean Surface

The ocean surface latent heat is later released when the air begins to rise and water vapor condenses into clouds and rain

References Ashley Proctor Samone Proctor Chelsea Addison

(3) Australian Government Bureau of Meteorology. (2009). About Tropical Cyclones. Retrieved November 22, 2009, from http://www.bom.gov.au/weather/cyclone/about/about-tropical-cyclones.shtml

(8) 1970 Bhola cyclone. (2009, November 22). In Wikipedia, The Free Encyclopedia. Retrieved November 23, 2009, from http://en.wikipedia.org/wiki/1970_Bhola_cyclone

(1) Catto, N., Hyndman, D., Hyndman, D. (2009). Natural Hazards and Disasters. Toronto, ON: Nelson Education

(6) Earth Science Australia. (2009). Tropical Cyclones. Retrieved November 22, 2009, from http://earthsci.org/flood/J_Flood04/cyclone/cyclone.html

(4) National Weather Service. (2008, October 8). Tropical Weather. Retrieved November 22, 2009, from http://oceanservice.noaa.gov/education/yos/resource/JetStream/tropics/tc.htm

(5) Nelson, S.A. (2009, October 30). Exceptional Weather – Tropical Cyclones. Retrieved November 22, 2009, from http://www.tulane.edu/~sanelson/geol204/tropical_cyclones.htm

(2) Tropical cyclone. (2009, November 22). In Wikipedia, The Free Encyclopedia. Retrieved November 20, 2009, from http://en.wikipedia.org/wiki/Tropical_cyclone

(7) WikiAnswers. (2009). How do cyclones form? Retrieved November 23, 2009, from http://wiki.answers.com/Q/How_do_cyclones_form&alreadyAsked=1&rtitle=What_causes_cyclones