Lightning Currents and Electric Field Measured at the Peissenberg Telecommunication Tower F. Heidler University of Federal Armed Forces, Munich, Germany Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Overview Introduction –Peissenberg Tower Overview about the Peissenberg Measuring Station –First period: Data acquisition up to the year 1999 –Second period: Data acquisition since 2008 Measurement results –First negative return stroke –Subsequent negative return stroke –“Self-initiated“ negative upward lightning –„Other-triggered“ negative upward lightning –“Self-initiated“ positive upward lightning –„Other-triggered“ positive upward lightning Comparison and conclusion

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Peissenberg - Station Current measurement –at the tower top (160 m) Measuring cabin (~ 190 m from tower) –Slow-electric field antenna –Fast speed camera (1000 frames/s) Slow-field antenna

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Location of the Peissenberg tower

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Measuring periods of the Peissenberg Station First measuring period from (1972) 1992 to 1999 Second measuring period since 2008 Replacement of the tower top section in 2007

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich First period: Data acquisition up to the year 1999 Recording of the slow-varying current with 2 channels of a DSO with different sensitivities –Duration: 1 s –Pre-trigger time: 100 ms –Sample interval: 1 µs. Recording of the fast-varying current/current derivative with 10 channels of a DSO –Duration: 50 µs –Sample interval:10 ns. Recording of the electric field (time-correlated) with 2 channels of a DSO with different sensitivities –Duration: 1 s –Pre-trigger time 100 ms –Sample interval 1 µs High speed video camera (time-correlated) –1000 images/s –1,6 s duration of the recording –Pre-trigger time: 0.5 s

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Second period: Data acquisition since 2008 Recording of the current with 2 channels of a DSO with different sensitivities –Duration: 2,56 s –Pre-trigger time: 0,5 s –Sample interval: 10 ns Recording of the electric field (time-correlated) with 2 channels of a DSO with different sensitivities –Duration: 2,56 s –Pre-trigger time: 0,5 s –Sample interval: 10 ns High speed video camera (time-correlated) –5000 images/s –1,4 s duration of the recording, –pre-trigger time: 0,6 s

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Types of lightning Lightning strikes to the Peissenberg tower Ground-to-Cloud Lightning (Upward Lightning) Cloud-to-Ground Lightning (Downward Lightning) Negative Positive Negative Positive First Stroke Subsequent Stroke First Stroke Subsequent Stroke Self- Initiated Other- Triggered Self- Initiated Other- Triggered

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich First negative return stroke Electric field exhibits a field change of opposite polarity prior to the current onset The electric decreases by the approach of the downward leader. The electric field rises rapidly with the onset of the return stroke current. This sequence builds up a V-shape of the electric field. The bottom of the V-shape is time- correlated with the initiation of the return stroke current. The same behavior was found in measurement from other-triggered upward lightning, where the electric field also exhibits a change of opposite polarity prior to the current onset Electric field, KV/m Time, ms 2 Electric field Current Connecting leader phase Return stroke phase V-shape Time, ms Current, kA Negative first stroke measured on August, 22, 2011 (ID #331);

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich First negative return stroke Current, kA Time, µs kA kA Negative first stroke measured on July, 03, 2015 (ID #365) µs First Maximum: - 44 kA Current, kA Time, ms Negative first stroke measured on July, 21, 1998 (ID #264). Flash I p (kA) T (µs) Q (C) ∫i 2 dt (A 2 s) # (-54.5) 25 (7.2) ~ 31- # ·10 3 # (-44) 50 (7.9) 684.4·10 6 AM ·10 6 Current Parameters I p : Peak current T %-to-90% risetime of the current Q: Charge ∫i 2 dt: Specific energy AM: Arithmetic Mean All of the three flashes consisted only a first return strokes (no subsequent stroke).

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Subsequent negative return stroke Fast-rising current –Oscillations in the current front –Oscillations caused by the transient response of the tower –The pulsation increased the rise time of the current at the tower top and limited the current steepness Slow-rising current –Not affected by oscillations Fast-rising current with oscillations (#b252) Slow-rising current without oscillations (#b227)

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Subsequent negative return stroke Measuring period Sample sizeArithmetic meanMaximum First period from 1992 to 1999 IpIp kA21 kA di/dt max 6845 kA/μs155 kA/μs Second period since 2008IpIp 3810 kA41 kA 10 Cumulative frequency,% (Probability) ,9 0,1 Cumulative frequency,% (Probability) ,9 0,1 Current peak I p, kA Maximum current steepness di/dt max, kA/µs (a) (b) 1 2 First measuring period

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich “Self-initiated“ negative upward lightning Constant field level prior to the onset of the upward lightning No lightning activity in the surroundings → „self-initiated“

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Charge of the “self-initiated” negative upward lightning

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Parameters of the electric field (~190 m) of the “self- initiated” negative upward lightning

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich „Other-triggered“ negative upward lightning (June 26, 1997) Current: –Transferred charge: 46.6 C Electric field –Bipolar electric field change with V-shape → „Other-triggered“ –Simultaneous field rise with the onset of the current –10-to-90% risetime: 9.4 ms Current, kA Time, s V-shape Fast rise Electric field, kV/m 0 Time, s Initiation of the current

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Positive upward lightning: Data overview 6 positive upward lightning from 1997 to 1999 –3 self-initiated positive upward lightning –3 other-triggered positive upward lightning Flash ID Date Time (UTC) Type Temperature (°C) Video Image Visibility conditions # :52: Self-initiated0.2yes Very poor, fog # :17: Other-triggered0.0yes Very good, no fog # :23:38.44 a Other-triggered 6.3yes Very good, no fog # :27:37.80 a Other-triggered 6.3yes Very good, no fog # :43: Self-initiated-2.0yes Very poor, fog # :45: Self-initiated-2.0yes Very poor, fog

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Self-initiated upward positive lightning ID #275 Parameters of the ICC Parameter Sample size UnitMinAMMax Charge of the ICC, Q 3C Duration of the ICC, t ICC 3ms Maximum of the pure ICC, i ICC 3kA Absolute current maximum, i max 3kA Pure electric field (189 m from the tower) Parameter Sample size UnitMinAMMax Field maximum, E max 3kV/m to-90% risetime, t ms Time on half value, t hv 3ms

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Self-initiated upward positive lightning Leader charge density: > 10 mC/m Initial field pulse train may last much longer compared to the initial current pulse train ID #275 Initial current pulse train Parameter Sample size UnitMinAMMax Peak value of the current pulse, i pulse 30kA Current pulse duration, t pulse 30µs51935 Inter-pulse interval, t interval 30µs72345 Pulse charge, Q pulse 30mC Duration of the pulse train, t train 3ms

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Other-triggered upward positive lightning ID #239 Parameter Sample size UnitMinAMMax Peak value of the current pulse, i pulse 30kA Current pulse duration, t pulse 30µs Inter-pulse interval, t interval 30µs Pulse charge, Q pulse 30mC Initial current pulses Parameters of the ICC Parameter Sample size UnitMinAMMax Charge of the ICC, Q 3C Duration of the ICC, t ICC 3ms Maximum of the pure ICC, i ICC 3kA Absolute current maximum, i max 3kA

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Other-triggered upward positive lightning ID #258 Subsequent current pulses Parameter Sample size UnitMinAMMax Peak value of the current pulse, i pulse 30kA Current pulse duration, t pulse 30µs Inter-pulse interval, t interval 30µs Pulse charge, Q pulse 30mC

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Other-triggered upward positive lightning ID b258

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Other-triggered upward positive lightning Parameter Sample size UnitMinAMMax Leader velocity 3m/s2 x x x 10 5 Average leader charge density 3mC/m Parameters of the upward leaders

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Other-triggered upward positive lightning ID b258 Parameter Sample size UnitMinAMMax Maximum electric field change, E max 3kV/m Bipolar electric field change, E ch 3kV/m Duration of the electric field change, t ch 3ms to-90% field risetime, t ms Parameters of the electric field

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Comparison between other-triggered and self-initiated positive upward lightning Other-triggered Self-initiated

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Comparison of the positive and negative self-initiated upward lightning

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Comparison between other-triggered lightning and return stroke Positive other-triggered upward lightning with ID #239Negative downward lightning with ID #259

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Conclusion The electric field of the other-triggered upward lightning exhibits an electric field change of opposite polarity prior to the onset of the current The electric field of the return strokes exhibits also an electric field change of opposite polarity prior to the onset of the current The waveform of the electric field has a V-shape –The first rising part of the V-shape was caused by an approaching downward leader. –The succeeding decreasing part of the V-shape was caused by the charge transfer due to the connection leader. →The other-triggered upward lightning is a downward lightning involving a very long upward leader!

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Types of ground lightning Downward leader Cloud charge Upward leader Pos. Downward (Return Stroke) Upward leader Cloud charge Pos. Upward (Self-Initiated) Upward leader Cloud charge Downward Leader Pos. Upward (Other –Triggered)

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Classification of the ground lightning acc. to the upward leader All of the ground lightning start with an upward leader Return strokes have upward leader with small length –Leader length:some 10 m up to more than 100 m Other-triggered upward lightning have upward leader with medium leader length –Leader length:some 100 m up to more than 1 km Self-initiated upward lightning have upward leader with large leader length –Leader length:some kilometres

Russian Conference on Lightning Protection (RCLP) St. Petersburg, May 17-19, 2016, Russia Prof. Dr. HEIDLER University of the Federal Armed Forces Munich Conclusion The initial phase of a return stroke process starts with a preliminary breakdown. The charges move in the thundercloud and the development of the streamers/leaders accumulates charges above the tower. When the accumulation of the charges exceeds a critical value, the electric field at the tower top gets so high that an upward leader is initiated. This upward leader makes contact to the leaders in or near the thundercloud (=> other-triggered upward lightning). Due to the field enhancement at the tower top, the critical value for the development of the upward leader is exceeded, if only a relatively small amount of charge is accumulated in the leaders in the thundercloud. Therefore, the other-triggered upward lightning develop, before the leaders in the thundercloud can come down to initiate an “classical” return stroke. That’s the reason, why only very few return strokes are measured at high towers. At the Peissenberg tower about 1-3 return strokes are expected yearly due to the tower height, but actually we have only about 1 return stroke in 10 years, on average.