2/26/09 12:11 PM Extratropical Cyclones Form at polar front Tropical Cyclones Masses of humid, warm rotating air Form within one air mass over ocean between 10 degrees and 25 degrees latitude Born as tropical depressions, low pressure zones in trade winds Must move over water of >26 degrees C Circular winds begin as warm air rises Wind speed <61 km/hr Become tropical storms if wind speed < 120 km/hr Become hurricanes, typhoons, tropical cyclones if wind speed > 120 km/hr Typhoon: same as tropical cyclone, it just depends on where you live Why do tropical cyclones rotate counter-clockwise? Coriolis Air starts moving toward a zone of low pressure and veers off course to right Core of tropical cyclone rotating to the left, or counterclockwise What fuels hurricanes and typhoons? Energy in a single hurricane is greater than all energy consumed in U.S. over past 20 years! Fundamental process is storage and release of latent heat Evaporating water stores vast latent heat of evaporation Condensing water in clouds (rain) releases that latent heat, drives winds About 100 form per year Liquid ? gas : use energy Gas ? liquid : get energy 2005 Hurricane Season in Atlantic ? the all-time record June-January: Arlene to Zeta Katrina: August 23-30 Rita: September 18-24 Wilma: October 17-25 Hurricane season: July to November July: sea surface temperatures aren?t warm enough for the strongest storms Saffir-Simpson Scale of Hurricane Intensity Determined by wind speed Category 5 is the strongest Different from tornado Categorize only based on the destruction it causes Destructiveness of hurricanes and typhoons Flooding by storm surge High winds Intense rainfall Flooding Landslides Hurricane Ike: September 2008 Storm surge Galveston Seawall Constructed after 1900 hurricane flood disaster to protect citizens and property Worked as designed during Ike Expensive beach homes built outside sea wall were destroyed Inland effects: Rainfall totals from Hurricane Ike Hurricane Galveston (1900) Deadliest US storm (~800 deaths) (Katrina ~1200) 8-15 foot tides flooded entire Galveston Island and Texan coast Property damage - $30 million Hurricane Katrina (2005) Costliest natural disaster in US (85 billion) 1200 lives lost Storm surge (28 ft) and flooding responsible for loss of life and property Combination of natural disaster, failed levees, people living below sea level in hurricane-prone area, and redirection of rivers Hurricane Rita (2005) Significant damage to oil refineries and oil platforms on the continental shelf A month after Katrina (Sept 24) Broke New Orleans levees again with storm surge Hurricane Wilma (2005) Strongest hurricane ever recorded in the Atlantic (winds over 185 mph, sustained) Damage to Cancun and Cozumel Struck Florida as Category 3 More Hurricanes? Stronger Hurricanes? Ocean Currents Currents are caused mainly by: Wind friction on the sea surface Differences in water mass density Surface currents affect uppermost 10% or so of the world ocean ? above pycnocline Deep water currents are driven by thermohaline convection - below pycnocline Surface currents are induced primarily by prevailing winds Coriolis Force plays a large part Oceanic Gyres **Know currents** 2/26/09 12:11 PM 2/26/09 12:11 PM
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