Lecture 25Outline of Last Lecture I. What is a Supercell?II. Hook EchoIII. Supercell StructureIV. Supercell EnvrionmentsV. Outbreak: SummaryVI. Supercell ComponentsVII. MesocycloneVIII. Supercell RotationIX. Wall CloudX. Mammatus CloudsXI. Forward Flank DowndraftXII. Rear Flank DowndraftXIII. Types of SupercellsOutline of Current Lecture XIV. TornadoesXV. Tornado StatisticsXVI. Where Do Tornadoes Form?XVII. Tornado LifecycleXVIII. Tornado TouchdownXIX. The Role of Downdraft- IdealizationXX. Multiple Vortex TornadoesXXI. Tornado DissipationXXII. Cyclic TornadogenesisATMS 100 1st EditionXXIII. Non-Supercell TornadoesXXIV. Tornado IntensityXXV. Enhanced Fujita ScaleXXVI. EF Scale- Well ConstructedXXVII. Tornado DestructionXXVIII. Tornado SafetyXXIX. Places that are not Safe/Places that areCurrent LectureXXX. Tornadoesa. a violently rotating column of air in contact with the ground pendant from a cumuliform cloudb. typically visible as a funnel cloudc. occur in all 50 states, though much more common in certain areasd. winds can range from 40 mph-300 mphXXXI. Tornado Statisticsa. average of 100 tornadoes reported in the US each yearb. average of 56 people killed and 975 injured by tornadoes each yearc. most tornadoes are short livedi. last only for a minute or twoii. some can last for up to an hour (or longer)XXXII. Where Do Tornadoes Form?i. most likely form in supercell thunderstorms1. about 1/4 of supercells produce tornadoes2. virtually all strong and violent tornadoes (F2 or greater) form in supercells3. look for hook echo indicating rotaton on radarii. Can occasionally form in squall lines/MCSs1. tend to be weakiii. Essentially never form in ordinary thunderstorms1. except for landsprouts and watersproutsXXXIII. Tornado Lifecyclea. Funnel Cloud formsb. Rotation makes contact with groundi. see dust or debris swirlii. mature stage- tornado is typically largest; most intenseiii. rope stage- tornado weakens and dissipatesXXXIV. Tornado Touchdowna. tornado touches down when circulation (NOT funnel) reaches the surfaceb. look for rotating debris (dust) in ground beneath fnnelXXXV. The Role of Downdraft- Idealizationa. Rear-flank downdraft transports circulation from aloft down to surfacei. downdraft can create additional rotation via tiltingb. rotating air converges and rises into updraft rotation amplifies rapidly via strechingc. relatively warm downdraft air more likely to rise in updraftXXXVI. Multiple Vortex Tornadoesa. strong tornadoes are often multiple vortex tornadoesi. less intense tornadoes have rising air in center, but central downdraft can form in strong tornadoesb. downdraft in center breaks circulation into smaller vorticesi. wind field is complex: must add tornado motion, rotaton of tor-nado, and rotation of suction vorticesii. one house may be destroyed, while house next door is notc. smaller vortices rotate around center of tornadoXXXVII. Tornado Dissipationa. liftetime ranges from minutes to an houri. not sure why some tornadoes last for a long time while others do notb. funnel becomes deformedi. winds blow in different direction aloft and near groundii. circulation forms a rope shapec. cloud outflow air wraps around tornadoi. air is not as buoyant, does not riseXXXVIII. Cyclic Tornadogenesisa. the same supercell can produce multiple tornadoes roughly parallel pathsXXXIX.Non-Supercell Tornadoesa. landspouts and waterspoutsi. pre-existing circulation at surface stretched by updraft (usually originates along wind shift line)ii. no downdraft or supercel requirediii. can occur in ordinary thunderstorms or MCSsiv. usually less intense than supercell tornadoes, but still danger-ousXL. Tornado Intensitya. tornado winds are generally not mesaured directlyb. intensity determined by damagei. depends on quality of constructionii. did tornado hit anything?c. enhanced fujita (EF) scale accounts for quality of constructioni. original fujita (F) scale was notXLI. EF Scale- Well Constructeda. EF0: Minor damage; roof shingles missing; tree limbs downb. EF1: Moderate; significant roof damage; damge to doors/windowsc. EF2: Considerable; roofs torn off; damage to exterior walls;large trees snapped and uprooted; mobile homes destroyedd. EF3: Severe; most walls onee. EF4: Devastating; Home completely leveledf. EF5: Extreme; Foundation wiped cleanXLII. Tornado Destructiona. storm spotter: can see tornadoi. tornadoes tough to see at night, in rain, in forested or hilly areasii. doppler radar is able to detect rotation within thunderstormXLIII. Tornado Safetya. go to interior room on lowest floor of a study structurei. basements preferredii. if on isn’t available, use closet or bathroomiii. stay away from windowsiv. protect yourself from flying debris if possibleXLIV. Places that are not Safea. Places that are not safe:i. carsii. mobile homesiii. highway overpassesiv. Large