Abstract
High-energy phenomena associated with lighting have been proposed in the twenties, observed for the first time in the sixties, and further investigated more recently by e.g. rocket triggered lightning. Similarly, x-rays have been detected in meter-long discharges in air at standard atmospheric conditions. Questions came up whether lightning triggered by aircraft would also generate hard radiation in-flight, its timing with respect to lightning current, its intensity and spectrum. In an earlier project, we developed a system ILDAS (http://ildas.nlr.nl) to determine the lightning current and its pattern over the aircraft with high accuracy and time-resolution. Later we added two x-ray detectors fore and aft in the aircraft.
In many flights X-rays were detected indeed associated with lightning strikes. Up to now we could attribute the observed x-rays to the lightning discharge initiation, first due to leader steps in the attachment phase of the lightning channel which lasts several milliseconds, and secondly during several microseconds before the recoil current pulses. Mostly the x-rays appeared to originate from the cathode spot on the aircraft. The required fast electrons are accelerated in the high electric fields in air just before the current starts.
In recent flights we observed a new phenomenon, a series of x-rays pulses lasting 8 microseconds, synchronous with the recoil current maximum of about 20 kA. From the current pattern and the relative intensity observed on both detectors, we again concluded that the x-ray originated somewhere in a region near the cathode, which was in this case the tail of the aircraft. The association with the current maximum is remarkable since an arc usually does not go with large electric fields. Arc jumps are a less likely because of the limited aircraft displacement. An alternative explanation is discharge initiation in the vicinity where the aircraft is not a part of that discharge current.
In the presentation we will address such phenomena, and also correlate observed currents in the aircraft with ground based measurements.
In many flights X-rays were detected indeed associated with lightning strikes. Up to now we could attribute the observed x-rays to the lightning discharge initiation, first due to leader steps in the attachment phase of the lightning channel which lasts several milliseconds, and secondly during several microseconds before the recoil current pulses. Mostly the x-rays appeared to originate from the cathode spot on the aircraft. The required fast electrons are accelerated in the high electric fields in air just before the current starts.
In recent flights we observed a new phenomenon, a series of x-rays pulses lasting 8 microseconds, synchronous with the recoil current maximum of about 20 kA. From the current pattern and the relative intensity observed on both detectors, we again concluded that the x-ray originated somewhere in a region near the cathode, which was in this case the tail of the aircraft. The association with the current maximum is remarkable since an arc usually does not go with large electric fields. Arc jumps are a less likely because of the limited aircraft displacement. An alternative explanation is discharge initiation in the vicinity where the aircraft is not a part of that discharge current.
In the presentation we will address such phenomena, and also correlate observed currents in the aircraft with ground based measurements.
| Original language | English |
|---|---|
| Title of host publication | AGU Fall Meeting 2016 |
| Publication status | Published - 12 Dec 2016 |
| Event | AGU Fall Meeting 2016 - San Francisco, United States Duration: 6 Dec 2016 → 12 Dec 2016 |
Conference
| Conference | AGU Fall Meeting 2016 |
|---|---|
| Country/Territory | United States |
| City | San Francisco |
| Period | 6/12/16 → 12/12/16 |