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Lecture 11

Lecture 11 - Tropical Cyclones.docx

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Earth Sciences
Sergei Basik

Earth Sci 2GG3 – L11 Lecture 11: Tropical Cyclones, Hurricanes and Typhoons Formation of Tropical Cyclones  The main development regions are between 5deg and 27deg north and south of the equator  Low pressure  warm air from ocean can rise and with it moisture is taken up  Convergence  low P system; then Diverge  Heat released as water condenses and then rises again  Necessary conditions for formation include:  Warm ocean water (>26.5C) to a depth of 20 m  Convergence of air masses to form areas of low pressure  Coriolis effect  Low wind speeds aloft  Growth of a Tropical Cyclone 1. Tropical Disturbance  Thunderstorms developed in a zone of convergence can cluster  Condensation and release of latent heat continues to warm air 2. Tropical Depression  Minimum wind speed of 40km/h ; Low P system  Convection spiral and rotation develops as warm air spirals upward  Decreasing pressure at the surface increases wind speed and subsequent evaporation 3. Tropical Storm  Minimum wind speeds of 62 km/h  Eye forms as warm air from the high-pressure aloft is sucked down into the centre 4. Tropical Cyclone  Officially becomes a tropical cyclone when sustained wind speeds exceed 119km/h  Structure of a Tropical Cyclone  Eye wall  most precipitation, highest wind speeds  Counterclockwise in Northern Hemi  Hurricane  Clockwise in Southern Hemi  Typhoon Tracking Tropical Cyclones  Track can be monitored by satellite  Thermal images measure storm intensity while Radar images can be used to estimate precipitation amounts (hotter faster it will move)  Hurricane tracks are predicted using weather forecast models which use data suck as ocean temperatures and location of other weather systems  Along the North Atlantic, hurricanes often follow the warm Gulf Stream  tend to then dissipate in cold North Atlantic  Saffir-Simpson Scale  Used to categorize tropical cyclones on the basis of maximum sustained wind speed (over a min of one minute) and barometric pressure  KNOW CHART!!!!! (know how to match wind speeds w. category of hurricane Earth Sci 2GG3 – L11 Damage from Tropical Cyclones  Cyclone Damage: Wave Damage  Extensive erosion as a result of wave damage  These waves are shorter than tsunami waves  Accretion – scoops up material and deposits on shore line after storm  Cyclone Damage: Storm Surge  Storm surges occur due to low atmospheric pressure and the strength of the winds in the tropical cyclone (set up).  The height of the storm surge also depends on the tidal cycle  During Hurricane Juan at Halifax, the height of the storm surge was almost as large as the tidal range ; had the storm coincided with the high tide, inland flooding would have been worse  In the Northern Hemi the highest wind speeds and largest storm surges are observed in the North to Northeast quadrant of tropical cyclone; here the direction of the winds are coupled with the movement of the storm  Bangladesh very vulnerabl
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