EL NINO, MONSOONS AND TROPICAL CYCLONES Physical and Chemical Oceanography Excellent link for understanding formation of 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  High productivity  large numbers of: Anchovies Sardines  Supports: substantial fisheries industry various sea bird species plankton-rich water

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  Surface temps decreased by 5 ⁰C  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 post- monsoon

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 HOW TROPICAL CYCLONES FORM Click on link!

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: North Atlantic = hurricane NW Pacific = typhoon Indian, S. Pacific (other) = tropical cyclone JAPAN FLORIDA CHINA 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