Slide 1Review: Tropical Cyclone IngredientsTropical Cyclone DevelopmentTropical Cyclone DevelopmentTropical Cyclone DevelopmentTropical Cyclone DissipationSlide 7Tropical Cyclone Structure - SatelliteSlide 9Slide 10Tropical Cyclone Structure - RadarSlide 12AirflowThe Stadium EffectThe Stadium EffectConservation of Angular MomentumWind Speeds and HeightSpiral BandsLeft and RightDestructive Forces in a Tropical CycloneTropical Cyclone WindsTropical Cyclone WindsExampleTropical Cyclones: Intensification, Structure, and WindsATMS-100Spring 2016Review: Tropical Cyclone Ingredients•Sea-surface temperatures (SSTs) greater than 26.5ºC•Deep layer of warm water in upper ocean•Cluster of thunderstorms–Usually in the form of a tropical disturbance or tropical wave•Moist air in the mid-troposphere•Weak vertical wind shear (<15 kts)•Latitude poleward of 5º–Coriolis force is zero at equator–Allows system to rotateTropical Cyclone DevelopmentHeating/divergence aloftPressures fallStronger PGF = Stronger windsStronger PGF = Stronger windsStronger winds = More heat and moisture (evaporation) transferred from ocean to atmosphereTropical Cyclone DevelopmentMore heat/moisture means stronger thunderstormsMore divergence aloftPressures falleven moreTropical Cyclone Development•Thunderstorms form near center of developing storm–Thunderstorms = RISING AIR–Air diverges aloft from thunderstorms–Divergence aloft creates low pressure at the surface•At surface, air flows counter-clockwise and inward toward center of low–As air moves over warm ocean, heat and moisture transferred from ocean to air•More heat/moisture rising means stronger thunderstorms, more divergence aloft, and lower pressure at center•Lower pressure means stronger PGF and stronger winds, and more heat/moisture transfer from sea•Another feedback mechanismTropical Cyclone Dissipation•Strong vertical wind shear–Rips storm apart•Moves over land–Ocean is source of heat and moisture–Mountains rip storm apart•Moves over cold water–Loses source of heat and moisture•Remains stationary for too long–Upwelling of cold water weakens stormTropical Cyclone Structure - Satellite•The eye (center; lowest pressure)–Clear and calm (and WARM)•The eyewall (strongest pressure gradient)–Strongest winds, heaviest rain, worst weather•Spiral bands–Outer portion of the stormhttp://www.youtube.com/watch?v=gUuG63EO6bs&NR=1http://cimss.ssec.wisc.edu/goes/blog/wp-content/uploads/2013/11/131107_coms1_ir_haiyan_anim.gifTropical Cyclone Structure - Radarhttp://www.youtube.com/watch?v=ZOGDahHgJp0EYEEYEWALLEYEWALLSPIRAL BANDS SPIRAL BANDSAirflow•Air spirals inward toward the eye at the surface–Requires Coriolis force•As air reaches the eyewall, it ascends through the eyewall to the tropopause–Air cannot penetrate tropopause because it is very stable•At upper levels, most of this air spirals outward anticyclonically (clockwise in NH)–Divergence aloft lower pressure at center of storm–Some of this air sinks in eye (sinking air prohibits cloud formation)The Stadium Effecthttp://cimss.ssec.wisc.edu/goes/blog/wp-content/uploads/2013/11/131106-07_coms1_vis_haiyan_eye_anim.gifThe Stadium Effecthttp://www.youtube.com/watch?v=eT5K6FR_eVsConservation of Angular Momentum•From physics:–Wind velocity x radius = Constant–V1r1 = V2r2–Radius = Distance from center of storm•As air spirals inward toward center of storm, radius decreases, so wind speed must increase!•Stadium effect: Eye has smallest diameter near surface, yielding strongest wind speeds near surface–Opposite of mid-latitude cyclones and jet stream (strongest winds near tropopause)Wind Speeds and HeightSpiral BandsLeft and Right•If you are moving with the storm, your right is the storm’s right•Your left is the storm’s left•Map notes:–The words “right” and “east” are never, ever interchangeable–The words “up” and “north” are never, ever interchangeableDestructive Forces in a Tropical Cyclone•Strong winds•Storm surge•Inland flooding•TornadoesTropical Cyclone Winds•Motion of storm toward NORTHTropical Cyclone Winds•Winds are strongest on the RIGHT side of circulation because storm motion and rotational winds are in same direction–Wind speeds are additive•They are in opposite directions on LEFT side of storm–Subtract–Weaker windsExample•Storm moving toward north at 25 knots•Wind speed = 100 knots•Winds on east side = ??•Winds on west side =