Lecture 11 Typhoons in Asia

8/8/2019 Lecture 11 Typhoons in Asia

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• Tropical cyclones

• Cyclone Nargis• Typhoon Vamei

Dr Adam D. Switzer

Singapore NRF Fellow & Nanyang Assistant Professor - Principal Investigator, Tectonics Group

Earth Observatory of Singapore | NTU N2-01A-04 Tel: (65) 6592-1762 Email: [email protected]



Coastal hazards II – Lecture objectives

At the end of this lecture you should be able to:

• Describe where tropical cyclones and mid latitude storms occur andwhy?

• Understand the difference between a storm and a cyclone.

• Explain with examples the saffir-simpson scale

• Comprehend the coriolis affect and how it relates to storms and

cyclones• Review Cyclone Nargis and the damage caused

• Understand the genesis of typhoon Vamei and why that storm isscientifically important.

Lakey, Sumbawa



Areas at Risk

• Northern hemisphere tropical cyclones:

– Rotate counterclockwise, track clockwise• Southern hemisphere tropical cyclones:

– Rotate clockwise, track counterclockwise



Tropical cyclones

• Tropical cyclones are also called Typhoons or Hurricanes

• Generally they form where water temperatures are above 26degrees in temperature.

• They are driven by the release of large amounts of latent heat which

occurs when moist air is carried upwards and water vapor condenses.



Hurricanes, Typhoons and Cyclones



Figure 6.7

• Pressure gradient:

high pressure low

pressure

• Pressure differences exist

due to unequal heating of

Earth’s surface

• Spacing between isobarsindicates intensity of

gradient

• Airflow is perpendicular to

isobars

Air pressure

gradients on

earths surface



• Large low pressure

cells are cyclones,(high pressure cellsanticyclones)

• Air driven towardsthe centre of acyclone due topressure gradientsgets deflected by

Coriolis to spiralaround the centre.

Cyclones



Coriolis effect on a rotating platform, as one person throws a ball to another person.

Freely moving objects on the surface of the Earth experience a

Coriolis force, and appear to veer to the right in the northernhemisphere, and to the left in the southern hemisphere.

Coriolis affect



• A cyclone has convergence near ground but divergence atupper level.

• An Anticyclone has divergence near ground, convergence atupper level.

Converge and divergence



Formation of Cyclones• Rising air and condensation can

build up into convective ‘chimney’of thunderstorms• Convection may strengthen when

air rises to high elevations withoutstrong winds to shear off anddissipate storms

• Begin to develop over warmseawater (26°C), between 5 and20 degrees latitude

• Vertical wind shear must beminimal

• Becomes cyclone force when windsexceed sustained velocity of 119km/hr

• Highest wind speeds exist alongedge of eye wall



Formation of Cyclones

• Warm, moist air rises and spreads

at top of chimney• Warm air expands, cools andreleases latent heat

• Eye of cyclone can be as much as20oC warmer than surrounding air

• Rising air pulls more air into

center of cyclone at low elevations• Storm may be from 160 to more

than 800 km in diameter• Forward motion averages 25

km/hr

• Wind speed and pressure dropabruptly in the eye.



Pressure and winds



Saffir-Simpson Hurricane Scale

– Based on barometric pressure and average wind speed

– Lower barometric pressure, stronger cyclone – Lower-category storms can do almost as much damage ashigher-category storms



Storm damage and deaths

• Global Costs related to cylcones have dramatically increased

– Rapidly growing populations along coast – More development in unsuitable locations

– More expensive buildings

• Number of deaths has decreased

– Improved ability to predict landfall locations – Coordinated ability to evacuate populations at risk



Tropical cyclones

World wide tropical cyclone tracks from 1985 to 2005.

Singapore



1000

TropicalDepression

9981008

Tropical Storm

1008

998

988978

Tropical cyclone

Pressure and winds

Intensity series

Formation and

anatomy of a

tropical cyclone

http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hurr/stages/ts.rxml







Water piling against the coast

Wind waves

Low pressure dome

Normal tidalrange

What is storm surge?

Water accumulates against the coast

Strong winds cause large short period waves

Low pressure at the surface causes a dome of water

Storm surge

Storm surge

Coast

Ocean



Case study - Cyclone Nargis

United States Department of State

Oth t i th i



Other events in the region

Tropical cyclone Nargis made

landfall on 2 May 2008,

causing the worst natural

disaster in Myanmar's

recorded history.

Official death toll estimates

exceed 138,000 making it theeighth deadliest cyclone ever

recorded worldwide.

The 1970 Bhola cyclone,

caused up to 500,000

fatalities.

Fritz et al., 2009

Nature Geosciences

C l N i 27 J l 3 M 2008



Hong Kong

Cyclone

Nargis’ path

Cyclone Nargis – 27 July - 3 May 2008

Tropical cyclone tracks from 1985 to 2005.

Singapore

Ti li t di t



Timeline to disaster

April 27 - the India

Meteorological Department

(IMD) classified the systemas a tropical depression

IMD upgrade it to cyclonic

storm Nargis.

April 28 - Nargis is nearlystationary and intensifying.

That day the Joint Typhoon

Warning Centre (JTWC)

upgraded the storm tocyclone status.

Ti li t di t




April 29 - JTWC estimated

Nargis reached winds of 160

km/h. IMD forecast landfallin Bangladesh or

southeastern India. Cyclone

becomes disorganized,

weakened and heads

northeast.

April 30 – cyclone intensifies

and heads to the east before

turning northeast on May 1





May 1 - Cyclone Nargis beganrapidly intensifying, due to thearrival of a new weather front.

May 2 - JTWC estimates thecyclone reached peak winds of 215 km/h (135 mph) as itapproached the coast of

Myanmar

May 1, 2008, visible image

from NASA's Atmospheric

Infrared Sounder

instrument on NASA's

Aqua spacecraft

H

Changes in intensity



Changes in intensity



Landfall and storm surge

May 2 - Cyclone Nargiscrossed the coast of

Myanmar with winds in

excess of 150km/hr, strong

waves and a storm surge

possibly up to 8m.

Researchers from the

University of Maryland

suggest that Cyclone Nargis

flooded about 14,402 km2 in

the Irrawaddy River Delta.

Gulf of

Martaban

Storm surge damage from Cyclone Nargis



Storm surge damage from Cyclone Nargis

Fritz et al., 2009

Nature Geosciences

Flooding and



Flooding and

destruction

The United Nations

estimated in its report that1.5 million people were

"severely affected" by this

cyclone.

The storm has killed 77,738

people and left 55,917

others missing and 19,359

injured, according to the

official death toll from the

United Nations.

Flooding and



This small village waslocated about 27 km south

of Yangon, the country’s

largest city.

After the disaster, the trees

and buildings are

completely gone, replaced

by messy piles of rubble.

The fields are largely

submerged under brown

and green floodwater.

Flooding and

destruction

Flooded fields

Destroyed

villages

Ruined

infrastructure



Typhoon (tropical storm) Vamei

Singapore

The belt 300 kilometers either

side of the equator has been

considered tropical cyclone-

free… well.. Until Dec 27 2001?

Vamei brought flooding and landslides to

eastern Malaysia, causing US$3.6 million in

damage and five deaths.

December 27 2001 in the South China Sea 1 5 degrees N about 150km north of

http://en.wikipedia.org/wiki/Malaysia

http://en.wikipedia.org/wiki/Malaysia

http://upload.wikimedia.org/wikipedia/commons/4/4b/Vamei_2001_track.png



December 27, 2001, in the South China Sea, 1.5 degrees N, about 150km, north ofthe Equator weather forecasters note the appearance of Typhoon Vamei.

Analysis later revealed that a weak, quasi-stagnant disturbance off Borneo interactedwith a strong, cold surge off Asia that set up a background rotation when it hit the

island. When the surge met the local disturbance, spin happened, and a typhoonrapidly emerged causing strong winds in both hemispheres..

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Lecture 11 Typhoons in Asia