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Lightning,Thunder andTornados

PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Electricity

Lightning

lightning: an electrical discharge in the atmosphere

I cloud-to-cloud (80%)

I cloud-to-ground (20%)

PHYS 189 () Lightning, Thunder and Tornados week 12 1 / 40


PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Electricity

Fundamentals of electricityElectrostatics

I electrical charges are either positive or negative

I charge is measured in Coulombs

I it takes 6× 1019 electrons to have one Coulomb ofcharge

I an electrical force exists whenever there is an unequalamount of positive and negative charges

I an electrical force is created when charges aretransferred from one material to another

I electrical charge is conserved (it is neither created ordestroyed)



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Electricity

Properties of electricity

q is the symbol for charge

current: measure of charge flow (I = ∆q/∆t)

voltage: potential difference between a negativelycharged object and a positively charges one(like terminals on a battery); also the electricpotential



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Electricity

Voltage=electric potential 6=electric potentialenergy

I electrical energy and electrical potential(www.regentsprep.org)

I electric potential energy is equal to the work done tomove charges

I electric potential is the electric potential energy percharge!

I voltage is the same as electric potential

I electric potential is not the same as electric potentialenergy!

I electric potential exists when there is chargeseparation


http://www.regentsprep.org/Regents/physics/phys03/apotdif/default.htm

http://www.regentsprep.org/Regents/physics/phys03/apotdif/default.htm


PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Electricity

Clicker question

You have a 1.5 V “AA” battery and a 1.5 V “D” cellbattery. Which one does more work for each Coulomb worthof charge that moves from the negative to the positiveterminal?

A. AA

B. D

C. they perform the same amount of work per Coulomb

D. not enough information given



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Electricity

Clicker question

You have a 1.5 V “AA” battery and a 1.5 V “D” cellbattery. Which one has more Coulombs worth of chargestored in the cell?

A. AA

B. D

C. they have the same amount charge




PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Electricity

Clicker question

You have a 1.5 V battery and a 12 V battery. Which onedoes more work for each Coulomb worth of charge thatmoves from the negative to the positive terminal?

A. 1.5 V

B. 12 V

C. they perform the same amount work per Coulomb




PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Electricity

Clicker question

You have a 1.5 V battery and a 12 V battery. Which one hasmore Coulombs worth of charge stored in the cell?

A. 1.5 V

B. 12 V

C. they have the same amount of charge stored in the cell




PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Lightning

Charge separation in the atmosphere

Earth

Ionosphere

+

+ + + + +++++

+

+ ++

++

− − − −−−

−

−−

−−

??

??

An electric field results from the charge difference betweenatmosphere and the surface of the earth (fair weather electricfield)



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Lightning

Proposed charging mechanism in thunderstorms

Saunders 2008

I Electric field polarizes graupel particles

I smaller ice particles collide and strip off the positivecharge

I ice particle travels to the top of the cloud


http://cics.umd.edu/~rachela/data/Carrio/Saunders-ChargingSeparationMechanisms.pdf


PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Lightning

Proposed charging mechanism in thunderstorms

Saunders 2008


http://cics.umd.edu/~rachela/data/Carrio/Saunders-ChargingSeparationMechanisms.pdf


PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Lightning

Charge separation in cloud



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Lightning

Clicker question

Why don’t charges just flow continuously through the airand neutralize the atmosphere?

A. the negatively charged surface repels the negativecharges at the cloud base

B. air is a good electrical insulator

C. it does

D. nobody knows



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Lightning

Lightning via a stepped leader



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Lightning

Lightning: cloud to ground

1. charge separation within the cloud enhances the electricfield between the earth and the atmosphere

2. electric field begins to “break down” air between

3. stepped leader of negative charges forms from cloudtoward ground

4. positive streamer of positive charges form fromground to cloud

5. stepped leader and positive streamer meet, forming aconduit for charge transfer between cloud and ground



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Lightning

more info

I Langmuir Lab at NMT


http://www.ee.nmt.edu/~/langmuir/


PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Lightning

Clicker question

A. Cloud to ground lightning is always initiated withnegative charges in the stepped leader moving towardground.

B. Discharges in the electric field can happen withoutlightning going all the way to the ground.

C. A bolt from the blue is a figure of speech, not an actualphenomenon.

D. Sprites and blue jets are creatures in faerie tales, notelectrical phenomena.



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Lightning

Thunder

I electric current traveling in the lightning path heats theair until it explodes

I the shockwave from the explosion is a compressionwave, or sound wave, that we call thunder



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Lightning

Lightning safety

I Go inside (buildings or vehicles)

I avoid tall, high or exposed areas

I avoid open spaces

I avoid water

I NOAA Lightning safety


http://www.lightningsafety.noaa.gov/more.htm


PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Thunderstorms

Clicker question

Air mass thunderstorms

A. are thunderstorms which occupy an entire air mass

B. are rare, but extremely destructive

C. only last 10s of minutes because they create downdraftswhich cut off their moisture supply

D. occur near frontal boundaries



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Thunderstorms

Air mass thunderstorms

air mass thunderstorms: consist of a number of individualconvective updrafts (cells)

The life cycle of an air mass thunderstorm:

1. cumulus stage

2. mature

3. dissipative



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Thunderstorms

Air mass thunderstorm life cycle

air is uplifted, creatinginitial clouds which pre-moisten the environment



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Thunderstorms

Cumulus stage

During the cumulus stage,

I temperature decreases with height at the sat’dadiabatic lapse rate

I some of the cloud extends above the freezing level

I ice crystals form and grow by the Bergeron process

I the sky darkens below the thickening cloud &precipitation begins to fall



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Thunderstorms



heavy rain or graupel particlesdrag air toward the surface cre-ating downdrafts in the areas ofmost intense precipitation

6



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Thunderstorms

Mature stage

During the mature stage,

I precipitation, lightning and thunder are most intense

I the top of the cloud extend to stable layers of theatmosphere which prevent further uplift

I strong winds at top layers push ice particles to createthe classic thunderstorm anvil

I updrafts dominate the interior of the cloud, downdraftsoccur just outside the cloud boundary (perfectconditions for turbulence which entrain dry air intocloud)



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Thunderstorms



heavy rain or graupel particlesdrag air toward the surface cre-ating downdrafts in the areas ofmost intense precipitation

6 downdrafts eventuallyoccupy the entire cloudbase, cutting off thesupply of moisture



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Thunderstorms

Dissipative stage

During the dissipative stage,

I supply of moisture is cutoff by downdrafts associatedwith heavy precipitation

I precipitation diminishes, sky clears

I the cloud boundary “blurs” and becomes “fuzzy”; thisis associated with glaciation



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Thunderstorms

Clicker question

A. The glaciated parts of the cloud contains a mixture ofice crystals and supercooled water droplets.

B. Only about 20% of the condensed moisture in a cloudfalls as precipitation.

C. Few lightning events are associated with air massthunderstorms.

D. Air mass thunderstorms only support one convective cellat a time.



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Thunderstorms

Severe thunderstorms: definition

severe thunderstorms have

I wind speeds that exceed 93 km/hr (58 mph)

I hailstones larger than 1.9 cm in diameter

I or they spawn tornados



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Thunderstorms

Severe thunderstorms: characteristics

In severe thunderstorms

I downdrafts reinforce convective updrafts and thusintensify the storm

I are mesoscale phenomena (it has a size ranging from10’s to 100’s of km)

I can involve a cooperation of convective cells whichcluster; these are called mesoscale convectivesystems (MCSs)

I MCSs can last from 12 hours to several days

I can arise from supercells, which is made of a singleupdraft region (rather than a collection of smallercooperating cells)



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Thunderstorms

How do downdrafts reinforce updrafts in MCSs?

? ?

strong downdrafts associ-ated with precipitationgenerate outflow that hitsthe surrounding warmer air

-

causing the warm air to riseand thus reinforce updraftfor another convective cell



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Thunderstorms


? ?

strong downdrafts associ-ated with precipitation

generate outflow that hitsthe surrounding warmer air

-




PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Thunderstorms


? ?

strong downdrafts associ-ated with precipitationgenerate outflow that hitsthe surrounding warmer air

-




PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Thunderstorms

Generation of new cells in a mesoscale convectivecomplex (MCC)



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Thunderstorms

Squall lines

I linear band of individual storm cells ( 500 km long)

I usually form in warm sector of midlatitude cyclone infront of the cold front

I looking for squall lines


http://www.nws.noaa.gov/outlook_tab.php


PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Thunderstorms

Role of wind shear in squall lines



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Thunderstorms

Clicker questionSupercell storms

A. have diameters from 20-50 km

B. are usually more violent than MCCs or squall lines, eventhough they are smaller

C. consist of a single extremely powerful cell rather than acollection of smaller cells

D. are described by all of the above



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Tornadoes

Tornadoes

I yesterday’s news

I archive surface analysis

I yesterday’s official storm report


http://www.youtube.com/watch?v=pDak_S64MtE&feature=player_embedded

http://www.hpc.ncep.noaa.gov/html/sfc_archive.shtml

http://www.spc.noaa.gov/climo/reports/


PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Tornadoes

Clicker question

Which of the following statements about tornados is false?

A. Strong tornadic winds result from extremely largepressure gradients (100 mb/.1 km, compared to 35mb/1000 km difference in sea level pressure acrossNorth America).

B. The wind speed can be measured directly in a tornado(105-450 km/hr, or 65-280 mph).

C. They can span a wide range of sizes and last fromminutes to hours.

D. They normally travel northeastward at about 50 km/hr(30 mph), more or less.



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Tornadoes

Tornado Safety

I Stay inside, in a basement

I If no basement, go to interior of house. Cover yourselfwith a mattress.

I Evacuate a mobile home! If no fixed building exists, lieflat in the ground away from the mobile home.

I If driving, try to avoid tornado by driving at right anglesto path (they move southwest to northeast).

I If you cannot avoid path while driving, abandon vehicleand seek nearby shelter or run low to the ground awayfrom road.



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Tornadoes

Tornado formation

I need a mesocyclone (largevortex, example of how toget one shown in figure)

I contraction of themesovortex to a smallervortex increaseswindspeed byconservation of angularmomentum

I tornado genesis is actuallynot well understood



PHYS 189

Electricity

Lightning

Thunderstorms

Tornadoes

Tornadoes

NMT on Nova

I NOAA Lightning safety


http://www.pbs.org/wgbh/nova/physics/lightning.html

electricity lightning lightning, electricity lightning...

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