Lecture 18Outline of Last Lecture I. What is a Tropical Cyclone?II. Where do Tropical Cyclones Form?III. Tropical Cyclones Around the WorldIV. Hurricane TracksV. Hurricane NamesVI. Tropical Cyclones (Atlantic)VII. Hurricane FrequencyVIII. Hurricane IngredientsIX. Warm Sea Surface TemperaturesX. Warm WaterXI. ThunderstormsXII. No ThunderstormsXIII. Thunderstorms- ITCZXIV. Moist Mid- TroposphereXV. Vertical Wind ShearXVI. Hurricanes and El NinoXVII. Coriolis ForceOutline of Current Lecture XVIII. Review: Hurricane IngredientsXIX. Hurricane DevelopmentATMS 100 1st EditionXX.Hurricane DissispationXXI. Huricane Structure- SatelliteXXII. Hurricane Structure- RadarXXIII. Air FlowXXIV. The Stadium EffectXXV. Conservation of Angular MomentumXXVI. Left and RightXXVII. Destructive Forces in a HurricaneXXVIII. Hurricane WindsXXIX. ExampleCurrent LectureXXX. Review: Hurricane Ingredientsa. Sea-surface temperatures greater than 26.5 degree celciusb. deep layer of warm water in upper oceanc. cluster of thunderstormsi. usually in the form of tropical disturbance or tropical waved. moist air in mid-tropospheree. weak vertical wind shear (<15)f. latitude poleword of 5 degreesi. coriolis force is zero at equatorXXXI. Hurricane Developmenta. heating/divergence aloftb. pressure falls c. stronger pgf=stronger windsi. more heat and moisture (evaporation) transferred from ocean toatmosphere1. stronger thunderstormsd. Thunderstroms form near from center of developing stormi. thunderstorms=rising airii. air diverges aloft from thunderstromsiii. divergence aloft creastes low pressure at the surfacee. At the surface, air flows counter-clockwise and inward toward center oflowi. as air moves over warm ocean, heat and moisture transferred from ocean to airf. more heat/moisture rising means stronger thunderstorms, more diver-gence aloft, and lower pressure at the centerg. lower pressure means stronger PGF an stronger winds and more heat/moisture transfer from seah. Another feedback mechanismXXXII. Hurricane Dissispationc. Strong Vertical Wind Sheari. rips storm apartd. Moves over landi. ocean is source of heat and moistureii. mountains rip storm aparte. Moves over cold wateri. loses source of heat of moisturef. Remains stationary for to longi. upwelling of cold water weakens stormXXXIII. Huricane Structure- Satellitec. The eye (center;lowest pressure)i. clear and calm (and WARM)d. The eyewall (strongest pressure gradient)i. strongest winds, heaviest rain, worst weathere. Spiral bandsi. outer portion of the stormXXXIV. Hurricane Structure- RadarXXXV. Air Flowc. Air spirals inward toward the eye at the srufacei. requires coriolis forced. as air reaches the eyewall, it ascends through the eyewall to the tropopausei. Air cannot penetrate tropopause because it is very stablee. at upper levels, most of this air spirals outward anticyclonically (clock-wise in NH)i. divergence aloft lower pressure at center of stormii. some of this air sinks in the eye (sinking air prohibits cloud for-mation)XXXVI. Conservation of Angular Momentumc. From physics:i. wind velocity x radius = constantd. As air spirals inward toward center of storm, radius decreases so wind speed must increasee. Stadium Effect: i. eye has smallest diameter near surface, yielding strongest winds near surface1. opposite of mid-latitude cyclones and jet stream (strong-est winds near tropopause)XXXVII. Left and Rightc. If you are moving with the hurricane, your right is the hurricanes rightd. your left is the hurricanes lefte. map notesi. the words right and east are never, ever interchangeableii. the words up and north are never, ever interchangeableXXXVIII. Destructive Forces in a Hurricanec. strong windsd. storm surgee. inland floodingf. tornadoesXXXIX. Hurricane Windsc. mortion of storm toward NORTHd. winds are strongest on the right side of the circulation because storm motion and rotational winds are in the same directioni. wind speeds are additivee. they are in opposite direction on left side of stormi. subtractii. weaker windsXL.Examplec. storm moving toward north at 25 knotsd. wind speed= 100 knotse. winds on east = f. winds on