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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
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
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 2 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 3 / 40
Lightning,Thunder andTornados
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
PHYS 189 () Lightning, Thunder and Tornados week 12 4 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 5 / 40
Lightning,Thunder andTornados
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
D. not enough information given
PHYS 189 () Lightning, Thunder and Tornados week 12 6 / 40
Lightning,Thunder andTornados
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
D. not enough information given
PHYS 189 () Lightning, Thunder and Tornados week 12 7 / 40
Lightning,Thunder andTornados
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
D. not enough information given
PHYS 189 () Lightning, Thunder and Tornados week 12 8 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 9 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 9 / 40
Lightning,Thunder andTornados
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
PHYS 189 () Lightning, Thunder and Tornados week 12 10 / 40
Lightning,Thunder andTornados
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
PHYS 189 () Lightning, Thunder and Tornados week 12 10 / 40
Lightning,Thunder andTornados
PHYS 189
Electricity
Lightning
Thunderstorms
Tornadoes
Lightning
Proposed charging mechanism in thunderstorms
Saunders 2008
PHYS 189 () Lightning, Thunder and Tornados week 12 11 / 40
Lightning,Thunder andTornados
PHYS 189
Electricity
Lightning
Thunderstorms
Tornadoes
Lightning
Charge separation in cloud
PHYS 189 () Lightning, Thunder and Tornados week 12 12 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 13 / 40
Lightning,Thunder andTornados
PHYS 189
Electricity
Lightning
Thunderstorms
Tornadoes
Lightning
Lightning via a stepped leader
PHYS 189 () Lightning, Thunder and Tornados week 12 14 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 15 / 40
Lightning,Thunder andTornados
PHYS 189
Electricity
Lightning
Thunderstorms
Tornadoes
Lightning
more info
I Langmuir Lab at NMT
PHYS 189 () Lightning, Thunder and Tornados week 12 16 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 17 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 18 / 40
Lightning,Thunder andTornados
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
PHYS 189 () Lightning, Thunder and Tornados week 12 19 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 20 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 21 / 40
Lightning,Thunder andTornados
PHYS 189
Electricity
Lightning
Thunderstorms
Tornadoes
Thunderstorms
Air mass thunderstorm life cycle
air is uplifted, creatinginitial clouds which pre-moisten the environment
PHYS 189 () Lightning, Thunder and Tornados week 12 22 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 23 / 40
Lightning,Thunder andTornados
PHYS 189
Electricity
Lightning
Thunderstorms
Tornadoes
Thunderstorms
Air mass thunderstorm life cycle
air is uplifted, creatinginitial clouds which pre-moisten the environment
heavy rain or graupel particlesdrag air toward the surface cre-ating downdrafts in the areas ofmost intense precipitation
6
PHYS 189 () Lightning, Thunder and Tornados week 12 24 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 25 / 40
Lightning,Thunder andTornados
PHYS 189
Electricity
Lightning
Thunderstorms
Tornadoes
Thunderstorms
Air mass thunderstorm life cycle
air is uplifted, creatinginitial clouds which pre-moisten the environment
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 () Lightning, Thunder and Tornados week 12 26 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 27 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 28 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 29 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 30 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 31 / 40
Lightning,Thunder andTornados
PHYS 189
Electricity
Lightning
Thunderstorms
Tornadoes
Thunderstorms
How do downdrafts reinforce updrafts in MCSs?
? ?
strong downdrafts associ-ated with precipitation
generate outflow that hitsthe surrounding warmer air
-
causing the warm air to riseand thus reinforce updraftfor another convective cell
PHYS 189 () Lightning, Thunder and Tornados week 12 31 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 31 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 31 / 40
Lightning,Thunder andTornados
PHYS 189
Electricity
Lightning
Thunderstorms
Tornadoes
Thunderstorms
Generation of new cells in a mesoscale convectivecomplex (MCC)
PHYS 189 () Lightning, Thunder and Tornados week 12 32 / 40
Lightning,Thunder andTornados
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
PHYS 189 () Lightning, Thunder and Tornados week 12 33 / 40
Lightning,Thunder andTornados
PHYS 189
Electricity
Lightning
Thunderstorms
Tornadoes
Thunderstorms
Role of wind shear in squall lines
PHYS 189 () Lightning, Thunder and Tornados week 12 34 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 35 / 40
Lightning,Thunder andTornados
PHYS 189
Electricity
Lightning
Thunderstorms
Tornadoes
Tornadoes
Tornadoes
I yesterday’s news
I archive surface analysis
I yesterday’s official storm report
PHYS 189 () Lightning, Thunder and Tornados week 12 36 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 37 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 38 / 40
Lightning,Thunder andTornados
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 () Lightning, Thunder and Tornados week 12 39 / 40
Lightning,Thunder andTornados
PHYS 189
Electricity
Lightning
Thunderstorms
Tornadoes
Tornadoes
NMT on Nova
I NOAA Lightning safety
PHYS 189 () Lightning, Thunder and Tornados week 12 40 / 40
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