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Excellent link for understanding formation of cyclones Physical and Chemical Oceanography 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 Click on link! 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