1. Types of Lightning Intracloud: most frequent (can also have cloud to cloud) Cloud to ground Air discharge: from charged region to air Intercloud

2. Types of Lightning Bolt from Blue Spider Cloud-to-Air Intracloud & Cloud-to-Ground

3. The Lightning Discharge: How does it occur? Charge in cloud produces large electric fields and induces charge of opposite sign at ground Breakdown/Stepped leader development: The stepped leader is a series of short current bursts (~50 m long) that ionizes a column of air as it moves downward Attachment: The downward moving stepped leader reaches an upward moving leader from the ground establishing a complete channel of ionized air – good conductor of electricity Return stroke: large current wave follows ionized air channel formed by the stepped leader and neutralizes more charge in the cloud Stepped leaders and Return Strokes (what your eyes see)

4. The second return stroke follows the dart leader’s arrival at the ground site The second return stroke can discharge layers of charge located in other regions of the cloud A dart leader quickly follows the return stroke and re-ionizes the conducting channel Subsequent Return Strokes Average of 2-4 return strokes per flash (this produces a flicker that your eye detects)

5. Enough with these decades-old drawings, what does all this look like in real life? Negative CG with 11 return strokes and a 200 ms continuing current High-Speed Video via Tim Samaras

6. Thunder Thunder is always produced by lightning Lightning heats the air to approximately 50,000 o F (Sun is about 10,000 o F) Heating causes rapid expansion of air around the lightning strike Thunder is a shock wave due to this rapid heating –Ear responds to this wave energy © 1999 Steven L. Horstmeyer

7. Why, at times, is thunder not heard after a lightning flash? Speed of sound slower than speed of light –If strike is not right next to us, thunder will occur later –Count number of seconds between seeing lightning and hearing thunder and divide by 5, gives approximate distance to lightning in miles. Atmosphere may bend the sound wave Eddies may scatter sound waves –Depending on how far away from the strike you are, you may not hear the thunder

8. Since temperature decreases with height, the speed of a sound wave moving near the ground is faster than a sound wave above the ground. As a result, the sound wave is bent (refracted) upward as it moves away from its source (a lightning channel). Normally, thunder cannot be heard more than about 15 miles, or 25 kilometers from a lightning flash (storm). Audible zone

9. How do we detect lightning? Lightning is an electromagnetic and optical phenomena- we take advantage of these characteristics to both DETECT and LOCATE lightning Electromagnetic methodsOptical methods Magnetic direction finding Time-of-arrival Electric field magnitude Eyeballs (generally not as accurate) Photoelectric devices (sensitive to optical wavelengths where lighting exhibits maximum power) National Lightning Detection Network NASA Kennedy Space Center Electric Field-Mill Network New Mexico Tech. University Lightning Mapping Array Examples*Examples NASA Lightning Imaging Sensor NASA Optical Transient Detector DMSP Optical Line Scanner *these instruments are all deployed on satellites

10. Cloud-to-Ground Lightning (U.S. and Front Range) National Lightning Detection Network Flashes/km 2 /year 0.01 0.02 0.04 0.08 0.16 0.32 0.64 1.28 2.56 5.12 10.24 14.5 1995-99 1989-99 Fort Collins is in a relative “lightning hole” ! Florida is the lightning capital of the U.S.

11. Electric Field Mill Maritime Continent Thunderstorm Experiment MCTEX (Colorado State University) Tiwi Islands, N. Australia, 1997 E  Charge/Area Gauss’ Law E Sign of charge in clouds overhead; lightning Detection Magnetic Direction Finder (Electromagnetic Method) Voltage   magnetic Field*angle /  time Faraday’s Law Magnetic field Locating a cloud-to-ground lightning flash Antenna Angle With two or more DF antennas, the direction (angle) and range to a flash can be determined

12. Optical Sensor NASA MSFC Lightning observed by Space Shuttle Orbit altitude 220 miles NASA-TRMM Satellite Optical Detection of Lightning ( note other instruments on the satellite like a radar allow us to study the structure of lightning producing clouds) 375 mile swath Radar Optical Sensor

13. Global Lightning Observed from the NASA-OTD 10-1000 times more lightning over land than Ocean Global Flash Rate about 40 flashes per second

15. Intracloud to Cloud-to-Ground Lightning Ratio (IC:CG) Integrated satellite observations with NLDN

16. Via Steve Goodman LIS and OTD worked so well, why not put a similar instrument on a GOES satellite? Band: 777.4 nm

17. Applications of Lightning Observations – Severe Weather Prediction

18. Lightning Jump Severe weather (hail, winds, tornadoes) often occurs after a convective surge and a pulse in updraft strength Lightning flash rate is directly proportional to both updraft strength and the amount of graupel in a thunderstorm Williams et al. (1999)

19. VHF Lightning Mappers LMA LMA soon LDAR

20. LMA charge structure methods 1) Initiation in max E-field between charge regions of opposite polarity 2) Bi-directional breakdown 3) Negative breakdown is noisier at VHF 4) No charge structure w/o lightning 1) Initiation in max E-field between charge regions of opposite polarity 2) Bi-directional breakdown 3) Negative breakdown is noisier at VHF 4) No charge structure w/o lightning Courtesy K. Wiens Most VHF sources are negative breakdown through region of positive charge!

21. 29 June 2000 overview Positive CGs Max reflectivity ~ 70 dBZ, Max updraft ~ 50 m/s Classic supercell, CG lightning predominately Positive (Xs)

22. 29 June charge structure “Inverted” tripole in precipitation; dipole in updraft Lower negative charge present in region of +CGs Radar data time: 2325 UTC NLDN data time: 2320-2330 UTC LMA data time: 23:24:42-23:24:57 UTC (+CG supercell) Wiens et al. (2005)

23. Mobile Electric Field Ballooning National Severe Storms Lab. Observing layers of electrical charge Electric Field mill Preparing to launch into a severe storm  E/  Z  Charge/Volume (Gauss’ Law) + + EZ Q Q Q Q Q = Charge E = Electric field V = Volume Z = Height

24. Stolzenburg et al. (1998) Archetypal charge structure in MCSs Inferred via balloon soundings

25. Lightning in MCSs >90% in convective line; downward sloping into stratiform region

26. Most stratiform lightning flashes initiate in the convective line and show downward sloping into the stratiform region Lang et al. (2004, 2010) Lang and Rutledge (2008)

27. In situ initiation in the stratiform region Nearly always near melting level Lang and Rutledge (2008)

28. Transient Luminous Events (TLEs)

29. High-speed sprite video Halo precedes actual sprite, visual appearance of different sub-structures of sprite a function of altitude (air density) Phantom HSI, 5000 fps, 11 July 2011 (Tom Warner)

30. Sprites Caused by large charge moment change CG strikes, normally associated with enormous stratiform lightning flashes (100s of km) CMC = Q x Z (Wilson 1925) – Can be 1000s of C km Stresses upper atmosphere to point of dielectric breakdown Lang et al. (2011)

31. Gigantic Jets Discharges from the top of the thundercloud toward the ionosphere These and other jet features caused by charge imbalances in thunderstorms Krehbiel et al. (2008), Lu et al. (2011)