Physical and Chemical Oceanography III
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Transcript Physical and Chemical Oceanography III
Excellent link for understanding formation of cyclones
Physical and Chemical
Oceanography
SECTION 7 PART III: EL NINO, MONSOONS
AND TROPICAL CYCLONES
Normal Wind Pattern
El Nino (southern oscillation)
sequence of events occurring in
southern Pacific Ocean
Normal conditions
cold nutrient-rich water flows North along west
coast of S. America.
Upwelling of nutrients due to winds from the
South
plankton-rich water
High productivity
large numbers of:
Anchovies
Sardines
Supports:
substantial fisheries industry
various sea bird species
Normal vs. El Nino
El Nino Conditions
Every ~7-10 years
Winds stop blowing from East or SE
Warm equatorial water is blown by abnormal
winds from the West.
Pressure gradients in East and West Pacific are
reversed
Reverse in wind direction and equatorial currents
Large area of warm water forms = cold-water
species death
Upwelling stops
Nutrient supply to surface is reduced = lack of
nutrients = primary production rapidly decreases
Affects higher trophic levels
Collapse of commercial fish stocks
El Nino Example
Major event in 1982-83
Surface temps decreased by 5⁰C
Heavy rain in normally dry
eastern Pacific
Cause not known: possibly
global warming?
Monsoons
Asia = largest continent
Climate swing: hot/wet to cold/dry
Monsoon (rainy season) -
seasonal shift in wind of the Indian
Ocean
Land absorbs heat faster than sea, so
it heats up faster
In winter, sea is warmed but not land
Warm air over sea rises and is less dense
Draws in cooler northeasterly air from land
India: occurs during post-monsoon season:
October - December
Monsoon
Summer (May-August) = land
quickly heats and there is big
temp. difference between
Central Asia and Indian Ocean
Land air warms, is less dense, rises
Saturated air (water vapor) from
southwest over Indian Ocean
Thunderstorms
Very heavy rain (80% of India’s
annual)
September, land mass cools,
monsoon weakens & replaced
with a dry, northeast postmonsoon
Tropical Cyclone Formation
A low-pressure storm system
Thunderstorms, strong winds, heavy rain
Develop over warm sea (26.5°C),
low-pressure, high evaporation
Water vapor rises, cools, condenses and
releases large amount of heat energy
Latent heat of condensation
Further increases evaporation = stronger
development
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HOW TROPICAL CYCLONES FORM
Tropical Cyclone Formation
Earth rotation + Coriolis Effect
= cyclonic spin
North hemis. – counterclockwise
South hemis. – clockwise
Move across surface in direction
of prevailing winds
Path = track
Hurricanes (Typhoons)
Multiple names around the world:
• Indian, S. Pacific
• North Atlantic • NW Pacific = (other) =
tropical cyclone
= hurricane
typhoon
JAPAN
CHINA
FLORIDA
AUSTRALIA
Names
Hurricanes (Typhoons)
Destructive to coastal communities
High winds
Can exceed 90 km/hr (56 mph)
Gusts: 280 km/hr (174 mph)
Erosion of shore, damage to moored boats
Heavy rain
Widespread flooding (extends inland when
cyclone moves in)
Can benefit arid (dry) areas
Storm Surges (sea level increase)
Flooding of low-lying areas (drowning)
Replenish nutrients in coastal water
(increased productivity)
ACTIVITY: On the Map
The three names (where they are found)
Coriolis deflects to the right (arrows)
Cyclonic rotation
North hemisphere
South hemisphere