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Electricity Lightning, Thunder and Tornados Lightning PHYS 189 Electricity Lightning Thunderstorms Tornadoes lightning: an electrical discharge in the atmosphere PHYS 189 () Lightning, Thunder and Tornados week 12 1 / 40 Electricity Lightning, Thunder and Tornados Lightning PHYS 189 Electricity Lightning Thunderstorms Tornadoes 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 Electricity Fundamentals of electricity Electrostatics Lightning, Thunder and Tornados PHYS 189 Electricity I electrical charges are either positive or negative I charge is measured in Coulombs 1019 I it takes 6 × charge I an electrical force exists whenever there is an unequal amount of positive and negative charges I an electrical force is created when charges are transferred from one material to another I electrical charge is conserved (it is neither created or destroyed) PHYS 189 () Lightning Thunderstorms Tornadoes electrons to have one Coulomb of Lightning, Thunder and Tornados week 12 2 / 40 Electricity Properties of electricity Lightning, Thunder and Tornados PHYS 189 Electricity Lightning Thunderstorms q is the symbol for charge Tornadoes current: measure of charge flow (I = ∆q/∆t) voltage: potential difference between a negatively charged object and a positively charges one (like terminals on a battery); also the electric potential PHYS 189 () Lightning, Thunder and Tornados week 12 3 / 40 Electricity Voltage=electric potential6=electric potential energy Lightning, Thunder and Tornados PHYS 189 Electricity I electrical energy and electrical potential (www.regentsprep.org) I electric potential energy is equal to the work done to move charges I electric potential is the electric potential energy per charge! I voltage is the same as electric potential I electric potential is not the same as electric potential energy! I electric potential exists when there is charge separation PHYS 189 () Lightning, Thunder and Tornados Lightning Thunderstorms Tornadoes week 12 4 / 40 Electricity Lightning, Thunder and Tornados Clicker question PHYS 189 Electricity You have a 1.5 V “AA” battery and a 1.5 V “D” cell battery. Which one does more work for each Coulomb worth of charge that moves from the negative to the positive terminal? Lightning Thunderstorms Tornadoes 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 Electricity Lightning, Thunder and Tornados Clicker question PHYS 189 Electricity Lightning You have a 1.5 V “AA” battery and a 1.5 V “D” cell battery. Which one has more Coulombs worth of charge stored in the cell? Thunderstorms Tornadoes 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 Electricity Lightning, Thunder and Tornados Clicker question PHYS 189 Electricity Lightning You have a 1.5 V battery and a 12 V battery. Which one does more work for each Coulomb worth of charge that moves from the negative to the positive terminal? Thunderstorms Tornadoes 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 Electricity Lightning, Thunder and Tornados Clicker question PHYS 189 Electricity Lightning You have a 1.5 V battery and a 12 V battery. Which one has more Coulombs worth of charge stored in the cell? Thunderstorms Tornadoes 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 Lightning, Thunder and Tornados Charge separation in the atmosphere PHYS 189 Electricity Lightning Ionosphere + + + + + + + Thunderstorms + Tornadoes + + + + + − PHYS 189 () − − Earth − − − − − − + + − Lightning, Thunder and Tornados + − week 12 9 / 40 Lightning Lightning, Thunder and Tornados Charge separation in the atmosphere An electric field results from the charge difference between atmosphere and the surface of the earth (fair weather electric field) Ionosphere + + + + + + + Electricity Lightning Thunderstorms + Tornadoes + + + + + ? + + + ? ? ? − − Earth − PHYS 189 () PHYS 189 − − − − − − − Lightning, Thunder and Tornados − week 12 9 / 40 Lightning Proposed charging mechanism in thunderstorms I Electric field polarizes graupel particles Lightning, Thunder and Tornados PHYS 189 Electricity Lightning Thunderstorms Tornadoes Saunders 2008 PHYS 189 () Lightning, Thunder and Tornados week 12 10 / 40 Lightning Proposed charging mechanism in thunderstorms Lightning, Thunder and Tornados I Electric field polarizes graupel particles I smaller ice particles collide and strip off the positive charge Electricity ice particle travels to the top of the cloud Thunderstorms I PHYS 189 Lightning Tornadoes Saunders 2008 PHYS 189 () Lightning, Thunder and Tornados week 12 10 / 40 Lightning Proposed charging mechanism in thunderstorms Lightning, Thunder and Tornados PHYS 189 Electricity Lightning Thunderstorms Tornadoes Saunders 2008 PHYS 189 () Lightning, Thunder and Tornados week 12 11 / 40 Lightning Charge separation in cloud Lightning, Thunder and Tornados PHYS 189 Electricity Lightning Thunderstorms Tornadoes PHYS 189 () Lightning, Thunder and Tornados week 12 12 / 40 Lightning Lightning, Thunder and Tornados Clicker question PHYS 189 Electricity Lightning Why don’t charges just flow continuously through the air and neutralize the atmosphere? Thunderstorms Tornadoes A. the negatively charged surface repels the negative charges 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 Lightning via a stepped leader Lightning, Thunder and Tornados PHYS 189 Electricity Lightning Thunderstorms Tornadoes PHYS 189 () Lightning, Thunder and Tornados week 12 14 / 40 Lightning Lightning: cloud to ground Lightning, Thunder and Tornados PHYS 189 Electricity 1. charge separation within the cloud enhances the electric field between the earth and the atmosphere Lightning Thunderstorms Tornadoes 2. electric field begins to “break down” air between 3. stepped leader of negative charges forms from cloud toward ground 4. positive streamer of positive charges form from ground to cloud 5. stepped leader and positive streamer meet, forming a conduit for charge transfer between cloud and ground PHYS 189 () Lightning, Thunder and Tornados week 12 15 / 40 Lightning Lightning, Thunder and Tornados more info PHYS 189 Electricity Lightning Thunderstorms Tornadoes I Langmuir Lab at NMT PHYS 189 () Lightning, Thunder and Tornados week 12 16 / 40 Lightning Lightning, Thunder and Tornados Clicker question PHYS 189 Electricity A. Cloud to ground lightning is always initiated with negative charges in the stepped leader moving toward ground. Lightning Thunderstorms Tornadoes B. Discharges in the electric field can happen without lightning going all the way to the ground. C. A bolt from the blue is a figure of speech, not an actual phenomenon. D. Sprites and blue jets are creatures in faerie tales, not electrical phenomena. PHYS 189 () Lightning, Thunder and Tornados week 12 17 / 40 Lightning Lightning, Thunder and Tornados Thunder PHYS 189 Electricity Lightning Thunderstorms Tornadoes I electric current traveling in the lightning path heats the air until it explodes I the shockwave from the explosion is a compression wave, or sound wave, that we call thunder PHYS 189 () Lightning, Thunder and Tornados week 12 18 / 40 Lightning Lightning, Thunder and Tornados Lightning safety PHYS 189 Electricity Lightning Thunderstorms 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 Tornadoes week 12 19 / 40 Thunderstorms Lightning, Thunder and Tornados Clicker question PHYS 189 Electricity Lightning Thunderstorms Air mass thunderstorms Tornadoes A. are thunderstorms which occupy an entire air mass B. are rare, but extremely destructive C. only last 10s of minutes because they create downdrafts which cut off their moisture supply D. occur near frontal boundaries PHYS 189 () Lightning, Thunder and Tornados week 12 20 / 40 Thunderstorms Air mass thunderstorms Lightning, Thunder and Tornados PHYS 189 Electricity Lightning air mass thunderstorms: consist of a number of individual convective updrafts (cells) Thunderstorms Tornadoes 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 Thunderstorms Air mass thunderstorm life cycle Lightning, Thunder and Tornados PHYS 189 Electricity Lightning Thunderstorms Tornadoes air is uplifted, creating initial clouds which premoisten the environment PHYS 189 () Lightning, Thunder and Tornados week 12 22 / 40 Thunderstorms Lightning, Thunder and Tornados Cumulus stage PHYS 189 Electricity Lightning During the cumulus stage, Thunderstorms I temperature decreases with height at the sat’d adiabatic 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 Tornadoes week 12 23 / 40 Thunderstorms Air mass thunderstorm life cycle Lightning, Thunder and Tornados PHYS 189 Electricity Lightning Thunderstorms Tornadoes 6 air is uplifted, creating initial clouds which premoisten the environment heavy rain or graupel particles drag air toward the surface creating downdrafts in the areas of most intense precipitation PHYS 189 () Lightning, Thunder and Tornados week 12 24 / 40 Thunderstorms Lightning, Thunder and Tornados Mature stage PHYS 189 Electricity During the mature stage, Lightning I precipitation, lightning and thunder are most intense I the top of the cloud extend to stable layers of the atmosphere which prevent further uplift I strong winds at top layers push ice particles to create the classic thunderstorm anvil I updrafts dominate the interior of the cloud, downdrafts occur just outside the cloud boundary (perfect conditions for turbulence which entrain dry air into cloud) PHYS 189 () Lightning, Thunder and Tornados Thunderstorms Tornadoes week 12 25 / 40 Thunderstorms Air mass thunderstorm life cycle Lightning, Thunder and Tornados PHYS 189 Electricity Lightning Thunderstorms Tornadoes air is uplifted, creating initial clouds which premoisten the environment downdrafts eventually occupy the entire cloud base, cutting off the supply of moisture heavy rain or graupel particles drag air toward the surface creating downdrafts in the areas of most intense precipitation PHYS 189 () 6 Lightning, Thunder and Tornados week 12 26 / 40 Thunderstorms Lightning, Thunder and Tornados Dissipative stage PHYS 189 Electricity Lightning During the dissipative stage, I supply of moisture is cutoff by downdrafts associated with heavy precipitation I precipitation diminishes, sky clears I the cloud boundary “blurs” and becomes “fuzzy”; this is associated with glaciation PHYS 189 () Lightning, Thunder and Tornados Thunderstorms Tornadoes week 12 27 / 40 Thunderstorms Lightning, Thunder and Tornados Clicker question PHYS 189 Electricity Lightning A. The glaciated parts of the cloud contains a mixture of ice crystals and supercooled water droplets. Thunderstorms Tornadoes B. Only about 20% of the condensed moisture in a cloud falls as precipitation. C. Few lightning events are associated with air mass thunderstorms. D. Air mass thunderstorms only support one convective cell at a time. PHYS 189 () Lightning, Thunder and Tornados week 12 28 / 40 Thunderstorms Severe thunderstorms: definition Lightning, Thunder and Tornados PHYS 189 Electricity Lightning Thunderstorms Tornadoes 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 Thunderstorms Severe thunderstorms: characteristics Lightning, Thunder and Tornados PHYS 189 In severe thunderstorms Electricity downdrafts reinforce convective updrafts and thus intensify the storm Lightning I are mesoscale phenomena (it has a size ranging from 10’s to 100’s of km) Tornadoes I can involve a cooperation of convective cells which cluster; these are called mesoscale convective systems (MCSs) I MCSs can last from 12 hours to several days I can arise from supercells, which is made of a single updraft region (rather than a collection of smaller cooperating cells) I PHYS 189 () Lightning, Thunder and Tornados Thunderstorms week 12 30 / 40 Thunderstorms How do downdrafts reinforce updrafts in MCSs? Lightning, Thunder and Tornados PHYS 189 Electricity Lightning Thunderstorms Tornadoes PHYS 189 () Lightning, Thunder and Tornados week 12 31 / 40 Thunderstorms How do downdrafts reinforce updrafts in MCSs? Lightning, Thunder and Tornados PHYS 189 strong downdrafts associated with precipitation Electricity Lightning Thunderstorms Tornadoes ? ? PHYS 189 () Lightning, Thunder and Tornados week 12 31 / 40 Thunderstorms How do downdrafts reinforce updrafts in MCSs? Lightning, Thunder and Tornados PHYS 189 strong downdrafts associated with precipitation generate outflow that hits the surrounding warmer air ? ? PHYS 189 () Electricity Lightning Thunderstorms Tornadoes - Lightning, Thunder and Tornados week 12 31 / 40 Thunderstorms How do downdrafts reinforce updrafts in MCSs? Lightning, Thunder and Tornados PHYS 189 strong downdrafts associated with precipitation generate outflow that hits the surrounding warmer air causing the warm air to rise and thus reinforce updraft for another convective cell ? ? PHYS 189 () Electricity Lightning Thunderstorms Tornadoes - Lightning, Thunder and Tornados week 12 31 / 40 Thunderstorms Generation of new cells in a mesoscale convective complex (MCC) Lightning, Thunder and Tornados PHYS 189 Electricity Lightning Thunderstorms Tornadoes PHYS 189 () Lightning, Thunder and Tornados week 12 32 / 40 Thunderstorms Lightning, Thunder and Tornados Squall lines PHYS 189 Electricity Lightning Thunderstorms I linear band of individual storm cells ( 500 km long) I usually form in warm sector of midlatitude cyclone in front of the cold front I looking for squall lines PHYS 189 () Lightning, Thunder and Tornados Tornadoes week 12 33 / 40 Thunderstorms Role of wind shear in squall lines Lightning, Thunder and Tornados PHYS 189 Electricity Lightning Thunderstorms Tornadoes PHYS 189 () Lightning, Thunder and Tornados week 12 34 / 40 Thunderstorms Clicker question Supercell storms A. have diameters from 20-50 km B. are usually more violent than MCCs or squall lines, even though they are smaller C. consist of a single extremely powerful cell rather than a collection of smaller cells Lightning, Thunder and Tornados PHYS 189 Electricity Lightning Thunderstorms Tornadoes D. are described by all of the above PHYS 189 () Lightning, Thunder and Tornados week 12 35 / 40 Tornadoes Lightning, Thunder and Tornados Tornadoes PHYS 189 Electricity Lightning Thunderstorms 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 Tornadoes Lightning, Thunder and Tornados Clicker question PHYS 189 Which of the following statements about tornados is false? A. Strong tornadic winds result from extremely large pressure gradients (100 mb/.1 km, compared to 35 mb/1000 km difference in sea level pressure across North America). Electricity Lightning Thunderstorms Tornadoes 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 from minutes 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 Tornadoes Lightning, Thunder and Tornados Tornado Safety PHYS 189 Electricity I Stay inside, in a basement I If no basement, go to interior of house. Cover yourself with a mattress. I Evacuate a mobile home! If no fixed building exists, lie flat in the ground away from the mobile home. I If driving, try to avoid tornado by driving at right angles to path (they move southwest to northeast). I If you cannot avoid path while driving, abandon vehicle and seek nearby shelter or run low to the ground away from road. PHYS 189 () Lightning, Thunder and Tornados Lightning Thunderstorms Tornadoes week 12 38 / 40 Tornadoes Lightning, Thunder and Tornados Tornado formation PHYS 189 Electricity I need a mesocyclone (large vortex, example of how to get one shown in figure) I contraction of the mesovortex to a smaller vortex increases windspeed by conservation of angular momentum I tornado genesis is actually not well understood PHYS 189 () Lightning, Thunder and Tornados Lightning Thunderstorms Tornadoes week 12 39 / 40 Tornadoes Lightning, Thunder and Tornados NMT on Nova PHYS 189 Electricity Lightning Thunderstorms Tornadoes I NOAA Lightning safety PHYS 189 () Lightning, Thunder and Tornados week 12 40 / 40
