Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Tropical Meteorology Jeff Gawrych Met. 10 Introduction • Tropical weather is very different than our mid-latitude weather. – No fronts, little day-to-day variation • Tropical weather systems form due to warm air rising (convection). • Thermodynamics says – Heat added to system will increase the temperature and increase ability to perform work • Warm oceans are fuel • Latent heat release when warm air rises and condenses • Tropical storms and hurricanes act like heat engines Background • Tropical cyclones/Hurricanes are perhaps the most severe of the weather phenomena. They can cause both massive property damage and loss of life. – in 1972 a TC killed an estimated 300,000-500,000 people in Bangladesh. – in 1992 Hurricane Andrew hit the southern US. – in 1999 created massive flooding & mud slides in Honduras and Guatemala – in 2004, 4 hurricanes hot the Florida coast. Charley, Frances, Ivan, Jeanne. – http://www.cnn.com/SPECIALS/2004/hurricanes/interactive/hurrican e.paths/index.html ITCZ • Inter-Tropical Convergence Zone – defined as the result of the equatorial Hadley cell where air converges near the equator, rises and diverges near the tropopause • Creates large thunderstorms called hot towers. • Usually between 5 and 10 degrees latitude. Definition • • • • These phenomena are commonly known as Tropical Cyclones _______________ (Indian Ocean & South Pacific), Hurricanes* _______________ (Atlantic and Eastern Pacific) Typhoons _______________ (North Pacific). * Named for Carib god of evil: Huracan • Tropical storms differ considerably from mid-latitude cyclones: For example, tropical storms have – – Warm core – No fronts Strongest wind near the surface Stages of development •Tropical Disturbance: mass of thunderstorms with slight wind circulation Some organization •Tropical depression: some closed isobars and winds 20-34 knots (more organization) •Tropical storm: packed isobars, winds 35-64 knots •Hurricane: when winds above 64 knots (74 mph) Atlantic Hurricanes… • Begin with easterly waves – Form as the Sahara Desert intensely warms up in the summertime – Wind blows to the west at ~ 15 deg. N – Triggers thunderstorm formation Hurricane Classification Recipe for Tropical Cyclone Formation 1. Warm ocean temperatures (T> 80F): – Typical in subtropical Atlantic/Pacific in summer/early fall – N. H. hurricane season: June-November 2. Rotation: – Thunderstorms must organize to produce converging air Coriolis force=0 – Cannot form at equator 3. Weak winds: Strong wind can disrupt organization Hurricane movement • Steered by prevailing winds – Easterly winds of tropical latitudes – Westerly winds of middle latitudes • Middle latitude high/low pressure systems can cause quick changes in hurricane position. • Often challenging to predict!! Hurricane George Evolution • Tropical cyclones are driven by the warm ocean temperature • Thus, they will weaken and eventually die when they move over – – Evolution • Tropical cyclones are driven by the warm ocean temperature • Thus, they will weaken and eventually die when they move over – land or – colder waters. Formation 12% 12% 30% 7% 12% 15% 12% Hurricane Structure • Eye of hurricane – Extremely low pressure, – weak winds and generally clear skies • Eye wall – Intense thunderstorms – Strongest winds, heaviest precip • Spiral rain bands – Areas corresponding to upward motion and heavy rain – Alternating with rain free areas Why is eyewall the most intense part of the Hurricane? • Law of Conservation of angular momentum – Wind speed (v) X distance from axis of rotation (r) must remain constant • Close to eye --> r is small --> v must be large • Far from eye --> r is large --> v is small Hurricane Destruction • Winds can have speeds over 100mph. – Extensive damage to buildings and vegetation. • Storm surge: abnormal rise in ocean level responsible for most damage via flooding • Hurricane may spawn tornadoes.