Lecture 17Outline of Last Lecture I. Oceanic GyresII. Oceanic TemperatureIII. UpwellingIV. DefinitionsV. ENSO: Normal ConditionsVI. ENSO Warm Phase: El NinoVII. Effects of El NinoVIII. ENSO Cool Phase: La NinaIX. Are We Headed for El Nino?X. Historical ENSO Events?Outline of Current Lecture XI. What is a Tropical Cyclone?XII. Where do Tropical Cyclones Form?XIII. Tropical Cyclones Around the WorldXIV. Hurricane TracksXV. Hurricane NamesXVI. Tropical Cyclones (Atlantic)XVII. Hurricane FrequencyXVIII. Hurricane IngredientsATMS 100 1st EditionXIX.Warm Sea Surface TemperaturesXX. Warm WaterXXI.ThunderstormsXXII. No ThunderstormsXXIII. Thunderstorms- ITCZXXIV. Moist Mid- TroposphereXXV. Vertical Wind ShearXXVI. Hurricanes and El NinoXXVII. Coriolis ForceCurrent LectureXXVIII. What is a Tropical Cyclone?a. A tropical cyclone is a low pressure system that develops over the tropical oceans of the worldi. tropical cyclones often move into the middle latitudes or over land areasb. they are the most destructive storms on the planetXXIX. Where do Tropical Cyclones Form?a. form over most tropical oceans of the world, but not right at the equatorXXX. Tropical Cyclones Around the Worlda. Typhoonsi. East of Asiab. Cyclone i. Northwest and North east of Austrailiaii. East of Africa iii. South of Europe c. Hurricanei. East of North America and West of MexicoXXXI. Hurricane Tracksa. Hurricane tracks determined by large-scale mid/upper tropospheric flow patterni. Geostrophic wind at 200 mbXXXII. Hurricane Namesa. Lists are used every six yearsi. alternating male and female namesb. seperatre list for each ocean basinc. a storm is only named when it reaches tropical storm strengthd. if a tropical cyclone caused a lot of damage or loss of life, its name is retiredi. Examples: Andrew, Hugo, Ike, Ivan, Katrina, Rita, WilmaXXXIII. Tropical Cyclones (Atlantic)a. Tropical Disturbance/Tropical Wave- Clusters of showers and thunderstormsi. tropical waves also known as African Easterly Wavesb. Tropical Depression- winds less than 39 mph (34 knots)c. Hurricane- strong tropical cyclone with winds greater than 74 mph (65 knots and eyewall developmentXXXIV. Hurricane Frequencya. Hurricanes and tropical storms most frequent between August and OctoberXXXV. Hurricane Ingredientsa. Sea-surface tempertaures (SSTs) greater than 26.5 degrees celciusb. deep layer of warm water in upper oceanc. clusters of thunderstormsi. usually in the form of a tropical disturbance or tropical waved. moist air in the mid-tropospheree. weak vertical wind shear (less than 15 kts)f. latitude poleward of 5 degreesi. Coriolis force is zero at equatorii. allows system to rotateXXXVI. Warm Sea Surface Temperaturesa. warm water adds heat and moisture to the lower tropospherei. aidsXXXVII. Warm Watera. Layer of warm water must be deep because hurricanes stir up the ocean as they move across iti. large waves mix warm surface water with cold deeper waterii. ocean temperature decreases with depthb. deep layer: does not mix cooler waterc. shallow layer: mixes up cooler waterXXXVIII. Thunderstormsa. important because they are the cloud systems from which hurricanes are bornXXXIX. No Thunderstormsa. no thunderstorms=no threat of hurricanes. b. can’t get a hurricane from clear skiesXL. Thunderstorms- ITCZa. belt of thunderstorms found near equatorb. NE trade winds in the Northern Hemisphere converge with SE tradewinds in the southern hemisphereXLI. Moist Mid- Tropospherea. Need moist air in mid-troposphere b. entrainment of dry air into circulation evaporates clouds and weakens systemXLII. Vertical Wind Sheara. the change in wind direction of wind speed with heightb. strong vertical shear=strong winds aloftc. bad for hurricanesi. rips them apartd. favorable for thunderstorms, tornadoes, mid-latitude cyclonesXLIII. Hurricanes and El Ninoa. strong vertical wind shear over the Atlantic ocean during El Nino suprresses hurricane formationXLIV. Coriolis Forcea. without CF, tropical cyclones will not rotatei. winds would flow directly toward the center of low pressureii. the low will dissipate quicklyb. CF effect forces winds to spiral in to the center of the stormi. allows system to rotatec. Tropical cyclones must be at least 5 degrees latitude away from the Equator i. CF zero at