Severe Storms:Severe Storms:Tropical CyclonesTropical CyclonesThunderstormsThunderstormsTornadoesTornadoes

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

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

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

Hurricane Structure

Computer model of hurricane wind structure

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.

Please Read

Hurricane Mechanics: Nuts and Bolts of Heat Engines

Hurricane Engine: Basic Operating Manualhttp://www.ems.psu.edu/~nese/ch11sec3.htm

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

westerlies4) Accelerated northward by mid-latitude winds

Energy Generated by a Hurricane

1. 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 1012 lightbulbs!

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.

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.

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

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 Camille200 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)

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.

Katrina, Aug. 29, 2005

For more information

National Hurricane Center http://www.nhc.noaa.gov

Tropical Meteorology Project at Colorado State University

http://typhoon.atmos.colostate.edu/

Thunderstorms, Lightning,Tornadoes

Anthes Ch. 5, pp. 124-32

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.

Lifecycle of a Thunderstorm

Supercell

Thunderstorm Climatology

Hail Climatology

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)

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.

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.

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.

Thunder

Thunder = sound waveLong 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 / secSpeed of sound ~ 0.33 km / sec3 second delay = 3 km; 5 second delay = 1 mile

Lightning fatalities

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

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.