Download 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