4.2.08 - Hurricanes, El Nino

4.2.08 - Hurricanes, El Nino - = 5.2 x 10 19 Joules/day or...

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Hurricanes; El Nino “Spin-up” phase (also called CISK): Conditional Instability of the Second Kind Air spirals into low P area: tropical depression Low-level convergence pushes air upwards Upward moving air cools o Clouds form o Latent heat released o Air aloft warms and expands Expanding air diverges aloft o Surface pressure drops (less weight) o Horizontal convergence reinforced SELF-REINFORCING FEEDBACK SYSTEM If the water is warm enough and there is no wind aloft: Depression Pressure drops until hurricane forms o The lower the pressure in the center, the stronger the hurricane Storm surge has two components Sea surface elevation (due to low P) Ocean surface setup (by winds) Surge height is related to Hurricane strength Category 1 (74-95 MPH) 1.5 Meters Category 2 (96-110 MPH) 2 Meters Category 3 (111-130 MPH) 3 Meters Category 4 (131-155 MPH) 4-5 Meters Category 5 (155+ MPH) >5 Meters Hurricanes transfer ocean heat to atmosphere Hurricane energy 1 day’s energy output
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Unformatted text preview: = 5.2 x 10 19 Joules/day or 6.0 x 10 14 Watts Storm strength dissipates when: Energy source (warm water) is lost • Storm moves over land • Storm moves over colder water El Nino – Southern Oscillation (ENSO) Coupled atmosphere-ocean phenomenon: • Trade winds • Sea Surface T • Rain patterns Characteristics of El Nino Originally observed by Peruvians: • Increased rainfall around December • Warming of surface ocean water • Disappearance of fish Now recognized as part of widespread phenomenon: • Unusually warm surface water across eastern Pacific • Changes in wind patterns • Drought is Australia and Indonesia • Violent storms along west coast of Americas Timing: • Twice/decade on average (but irregular) • Lasts 14 to 22 months • Usually begins in Jan-Feb, peaks Nov-Jan, then diminishes Evidence for El Nino over thousands of years Very variable: no two events are the same...
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This note was uploaded on 04/16/2008 for the course GEOS 104 taught by Professor Cox during the Spring '08 term at Williams.

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4.2.08 - Hurricanes, El Nino - = 5.2 x 10 19 Joules/day or...

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