Severe Storms: Tropical Cyclones Thunderstorms Tornadoes

1. Severe Storms: Tropical Cyclones Thunderstorms Tornadoes

2. Typhoon Lupit, which means "fierce" in Filipino, is taking dead aim at the already storm battered Philippines, which will make it the 18th typhoon to hit the country this season…Over the last month two storms, Ketsana and Parma, struck the country, causing flooding and landslides. Over 800 people were killed – ABC World News, Oct. 22, 2009. • t

3. Tropical Cyclones • Violent, long-lived cyclonic storms with sustained winds in excess of 74 mph that originate in tropical latitudes, usually in late summer and early autumn. • Hurricane -- W. Hemisphere, named for Mayan sky god Hurican (Sp. Huricán, Fr. Ouragan) • Typhoon -- W. Pacific, named for great wind (Cantonese) • Cyclones -- Indian Ocean and Australia

4. Saffir-Simpson Scale • NAME WINDS (mph) DAMAGE • Tropical depression 23-39 minor • Tropical storm 40-74 from rains • Hurricane CAT I 74-95 trees • CAT II 96-110 roofs • CAT III 111-130 light structures • CAT IV 131-155 extensive • CAT V > 155 devastating

5. Hurricane Structure

7. Computer model of hurricane wind structure

8. Hurricane Origins and Tracks • Formed by disturbance in trade winds near ITCZ. • Needs warm ocean water T > 26 oC • Needs Coriolis force to support rotation, so never found in latitudes less than 5o North or South • Needs conditions with no wind shear aloft to get organized. • Sustained by massive release of latent heat of condensation.

9. Please Read • Hurricane Mechanics: • Nuts and Bolts of Heat Engines • Hurricane Engine: Basic Operating Manual • http://www.ems.psu.edu/~nese/ch11sec3.htm

10. Hurricane’s Demise • Over land hurricanes are: • 1) Cut off from warm ocean moisture • 2) Slowed down by increased surface friction • 3) Torn apart by increased wind shear aloft in the westerlies • 4) Accelerated northward by mid-latitude winds

11. Energy Generated by a Hurricane • Rain formation: An average hurricane produces 1.5 cm/day of rain inside a circle of radius 665 km. Converting this to a volume of rain gives 2.1 x 1016 cm3/day. A cubic cm of rain weighs 1 gm. Using the latent heat of condensation, this amount of rain produced gives 5.2 x 1019 Joules/day or 6.0 x 1014 Watts. This is equivalent to 200 times the world-wide electrical generating capacity - an incredible amount of energy produced! And the storm can last for 10 days or so! This power would illuminate 6 x 1012lightbulbs! 2. Wind energy: Proportional to the the wind speed cubed. Using 40 m/s for an inner radius of 60 km yields 1.5 x 1012 Watts. So a hurricane produces an amazing amount of energy. 400 times more by rain formation than by wind energy.

12. Hazards of Tropical Cyclones • Torrential rains (10 inches is common), • Storm surges of as much as 25 feet (from low pressure, onshore winds, and high tides), • Flooding can be widespread. • Mud Slides in hilly terrain • Wind gusts of up to twice the average wind speed • Tornadoes and Thunderstorms embedded in the tropical storms • Storm track is somewhat erratic and is determined by the interaction of the storm with its environment.

13. Hurricane Andrew 1992 Last CAT 5 to hit U.S., 43 deaths, $30B damage.

14. Past Dealiest Hurricanes • 1900 Galveston hurricane, Isaac’s Storm (6,000 dead) • 1938 New England Hurricane (Miller video 1687) • The hurricane had no name, it was not tracked, and it came with little or no warning. There were no emergency services available. • Killer storm surge caused by extreme low pressure, offshore winds, and the timing of the high tide. Great loss of life. • 1969 Hurricane Camille • 200 mph wind gusts, 25 foot storm surge, 256 deaths, $4 Billion damage. • 1970 Bengal cyclone (500,000 dead) • 2005 Katrina (over 1800 deaths, mainly from flooding)

15. Hurricane Mitch (22 Oct.-5 Nov. 1998) • Mitch was responsible for over 9,000 deaths predominately from rain-induced flooding in portions of Central America, mainly in Honduras and Nicaragua. This makes Mitch one of the deadliest Atlantic tropical cyclones in history. • The 905 mb minimum central pressure and estimated maximum sustained wind speed of 155 knots (Category V) over the western Caribbean make Mitch the strongest October hurricane since records began in 1886.

17. Katrina, Aug. 29, 2005

20. For more information • National Hurricane Center • http://www.nhc.noaa.gov • Tropical Meteorology Project • at Colorado State University • http://typhoon.atmos.colostate.edu/

21. Thunderstorms, Lightning,Tornadoes Anthes Ch. 5, pp. 124-32

22. Thunderstormshttp://www.nssl.noaa.gov • A thunderstorm is a deep convective cloud (Cb) reaching as high as 10 to 18 km, that produces lightning, thunder, heavy rain, downbursts, possibly hail, flash floods, and on rare occasions, tornadoes. • It is a thermodynamic heat engine driven by the latent heat of condensation (vapor to liquid) and fusion (liquid to ice). • Can be caused by solar heating, nighttime cooling, sea breeze convergence, mountains, cold fronts. • An average of 1800 thunderstorms are active globally at this moment. • Mesoscale convective complex contains dozens of Cbs and is 1000 times larger than a thunderstorm.

23. Lifecycle of a Thunderstorm

24. Supercell

25. Thunderstorm Climatology • Hail Climatology

26. Lightning • Lightning is an electrical discharge. • Most flashes originate in clouds. • Clouds are “most commonly in a negative state of electricity, but sometimes in a positive state.” • Grounded metallic rods will protect most structures from damage. • Source: • Benjamin Franklin (1750s)

27. Lightning • Lightning is a giant transient high-current electrical discharge (or spark) of static electricity with a path length of kilometers. • A typical strike is 100 million volts, 100,000 amps, and generates temperatures of 30,000 K (five times hotter than the sun’s surface). • Around the world, there are 1800 thunder storms going on at any given time with 100 lightning strikes to Earth each second. • That means 9 million lightning bolts per day! • Most lighting is within a cloud or between clouds. • Only about 20% is cloud to ground.

28. Lightning strike details • Lightning strike is very fast and very complex: • 1. Cloud to ground stepped leader moves along a branching path in 20 to 100 meter steps at 10 to 20 km/sec. • 2. Ground to cloud return stroke covers the final 100 meter spark gap to a high spot (tree, tower, golf club). • 3. Subsequent (3-40) strokes called dart leaders give lightning its forked appearance, completing the strike.

29. Lightning formation • Necessary condition: Separation of charge. • Cb is a static electricity generator. • Charge separation caused by collisions of water and ice. • Electrons (-) and ions (+ -) transported to different levels via updrafts and downdrafts. • Air is a good insulator. • Cloud can reach 100 million volts, 100,000 amps. • Car battery is 12 volts, 8 amps. • House current is 120 volts, 20 amps. • Sufficient condition: Voltage difference > insulating ability of the air.

30. Thunder • Thunder = sound wave • Long tube of air, 6 km x 15 cm diameter heated almost instantaneously to 12-30,000 K expands air violently. • Shock wave = thunder (both audible and inaudible). • Speed of light = 300,000 km / sec • Speed of sound ~ 0.33 km / sec • 3 second delay = 3 km; 5 second delay = 1 mile

31. Lightning fatalities About 60 fatalities per year in the US, 360 severe injuries

32. Benefits of lightning • May have played a role in the pre-biotic formation of amino acids. • Fixes nitrogen, creates natural fertilizer. • Ignites forest fires -- forest ecology. • May have been the source of fire for early humans. • E-M fields of lightning used to study the atmosphere. • Global lightning strikes represent a global “thermometer.” • Lighting strikes on other planets (Jupiter) allow remote study.