ChapterChapter 88 continued…..continued….. ThreeThree typestypes ofof cyclones:cyclones:
1. Wave cyclones: cyclone/low
2. Tropical cyclone: hurricane/typhoon
3. Tornado LocalLocal SevereSevere WeatherWeather
` Flash Flooding ` Lightning ` High Winds ` Hail ` Tornadoes AirAir MassMass ThunderstormThunderstorm LifeLife CycleCycle AirAir MassMass ThunderstormThunderstorm LifeLife CycleCycle AirAir MassMass ThunderstormThunderstorm LifeLife CycleCycle •Downdrafts spread outward when they hit the ground and converge with the warmer surrounding air to form the outflow boundary. LifeLife--CycleCycle ofof aa ThunderstormThunderstorm
TotalTotal timetime cancan bebe lessless thanthan oneone hourhour
SupercellSupercell ThunderstormsThunderstorms SupercellSupercell ThunderstormThunderstorm overover LaPlataLaPlata,, MDMD AprilApril 20022002 InsideInside aa SupercellSupercell RadarRadar ImageImage ofof aa SupercellSupercell –– HookHook EchoEcho
ThunderstormsThunderstorms maymay groupgroup togethertogether asas aa MesoscaleMesoscale ConvectiveConvective ComplexComplex (MCC)(MCC) DownburstsDownbursts DeadlyDeadly DowndraftsDowndrafts
` Strong downdrafts may create downbursts ` Wind speeds can exceed 270 km/hr (170 mph). ` When strong downdrafts reach the surface, they can spread outward in all directions to form intense horizontal winds, capable of causing severe damage. ` Downbursts with diameters of less than 4 km are called microbursts Dangerous problem when they occur near airports. Geographic Distribution of Thunderstorms
` Thunderstorms develop where moist air is forced aloft
` Occurs frequently in the tropics, nearly daily in some locations
` In the United States, most frequent region is the Gulf South
` Highest incidence in Florida because it is almost completely surrounded by warm waters AverageAverage annualannual numbernumber ofof daysdays withwith thunderstormsthunderstorms Flash Flooding FLASHFLASH FLOODINGFLOODING More persons are killed by flash flooding than any other form of severe weather. An average of 135 persons die each year.
LightningLightning OnOn average,average, 44,00044,000 thunderstormsthunderstorms occuroccur aroundaround thethe worldworld everyevery day.day. AtAt anyany givengiven time,time, anan averageaverage ofof nearlynearly 20002000 thunderstormsthunderstorms exist.exist.
SinceSince eacheach thunderstormthunderstorm willwill generategenerate anan averageaverage ofof 100100 cloudcloud--toto--groundground lightninglightning strokes,strokes, thethe totaltotal dailydaily numbernumber ofof lightninglightning dischargesdischarges aroundaround thethe worldworld isis approximatelyapproximately 44 –– 55 MILLION!!MILLION!! MuchMuch ofof thethe energyenergy ofof aa lightninglightning dischargedischarge isis dissipateddissipated throughthrough thethe airair asas shockshock waveswaves thatthat wewe callcall thunderthunder Air heated to a temperature of 50,000°F in the conducting channel
LightLight travelstravels atat 300,000300,000 km/seckm/sec butbut soundsound waveswaves traveltravel atat onlyonly 0.330.33 km/seckm/sec ThusThus thethe thunderthunder isis heardheard afterafter thethe lightninglightning strokestroke ThunderThunder
` Caused by the rapid expansion of air from tremendous increase in temperature during a lightning stroke
` Lightning without thunder being heard called heat lightning Thunder is produced but stroke is too far away to reach an observer
` Rumbling thunder is typically caused by sound echoing off topographic features and buildings
` Slower speed of sound (vs. speed of light) causes a lag between the stroke and the resulting thunder
` To determine the distance in km, count the seconds between the stroke and thunder and divide by 3 (divide by 5 to determine distance in miles)
ChargeCharge SeparationSeparation –– InitiatingInitiating LightningLightning Leaders, Strokes, and Flashes
Development of Cloud-to-Ground Lightning Processes of Lightning Formation
(Source: http://thunder.msfc.nasa.gov/primer)
TypesTypes ofof LightningLightning –– ManyMany typestypes existexist
` St. Elmo’s Fire tall objects (e.g., church steeples) glow as ionization occurs in the air around them Blue-green tint, hissing sound
` Ball lightning may be the most unusual type