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. 2017 Dec 16;122(23):12801-12811.
doi: 10.1002/2017JD027405. Epub 2017 Dec 4.

In-Flight Observation of Gamma Ray Glows by ILDAS

Pavlo Kochkin  1 , A P J van Deursen  2 , M Marisaldi  1 , A Ursi  3 , A I de Boer  4 , M Bardet  4 , C Allasia  5 , J-F Boissin  5 , F Flourens  5 , N Østgaard  1
Affiliations

In-Flight Observation of Gamma Ray Glows by ILDAS

Pavlo Kochkin et al. J Geophys Res Atmos. .

Abstract

An Airbus A340 aircraft flew over Northern Australia with the In-Flight Lightning Damage Assessment System (ILDAS) installed onboard. A long-duration gamma ray emission was detected. The most intense emission was observed at 12 km altitude and lasted for 20 s. Its intensity was 20 times the background counts, and it was abruptly terminated by a distant lightning flash. In this work we reconstruct the aircraft path and event timeline. The glow-terminating flash triggered a discharge from the aircraft wing that was recorded by a video camera operating onboard. Another count rate increase was observed 6 min later and lasted for 30 s. The lightning activity as reported by ground networks in this region was analyzed. The measured spectra characteristics of the emission were estimated.

Keywords: ILDAS; aircraft; gamma ray; glow; lightning.

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Figures

Figure 1
Figure 1
The infrared HIMAWARI satellite map taken 5 min before the first glow. Temperature bar is indicated on the right side in degrees Celsius. The red regions with t≤−70° correspond to the Cloud Top Height CTH≥15 km. Two cloud regions are clearly separated. The WWLLN sferics (squares) are shown from 5 min before the first glow to 5 min after the second. Regions where the glows were detected are indicated.
Figure 2
Figure 2
The (top) electric field profile and (bottom) total X‐ray counts as recorded by CDF algorithm (spectrometer). The first glow was detected at 7:36 UTC and lasted for 20 s. The second glow was detected at 7:42 UTC and lasted for 30 s. The low electrical activity between 7:37 and 7:41 UTC corresponds to the aircraft transfer from one cloud to another.
Figure 3
Figure 3
The same as Figure 2 but zoomed on the first glow. The glow starts at 07:35:35 and lasts for 20 s. It is abruptly terminated by a lightning flash at 07:35:56 UTC. About 10 WWLLN and 15 LIAS sferics were reported during the glow. The ILDAS was triggered twice and recorded two 1 s long intervals in high‐resolution mode. They are indicated as 805D0DA4 and 005D11F5. Their precise timing is also shown.
Figure 4
Figure 4
The WWLLN (squares) and LIAS (circles) sferics detected during the first gamma ray glow. Their time is indicated in Figure 3 (top). The WWLLN position uncertainty is shown as a dashed 5 km radius circle around flash #3. WWLLN #3 and LIAS #4,5,6 interrupted the glow and triggered ILDAS. WWLLN #8 and LIAS #13 are 45 km away but were also detected and triggered ILDAS.
Figure 5
Figure 5
The glow‐terminating flash as detected by ILDAS in high‐resolution mode with the code 805D0DA4. X‐ray counts are binned in 15 ms intervals. The X‐ray intensity is higher before the electromagnetic (EM) pulse at t = 0 then after it.
Figure 6
Figure 6
The zoomed version of the EM pulse shown in Figure 5. Characteristic negative stepped leader signature is present at t =− 4 ms. Current pattern flowing through the aircraft at t =− 0.1 ms is indicated in the inset. Numbers are in A/m. The pattern corresponds to a scenario when a positive leader initiates from the right wing.
Figure 7
Figure 7
The video frame shows a leader channel attached to the right wing. The frame is taken at t = 07:35:55.760 UTC. A lightning leader is attached to the wing and pointed toward the nose. Ionization of the wingtip vortex is visible going along the aircraft path.
Figure 8
Figure 8
The second ILDAS trigger 005D11F5 caused by a distant lightning flash. Only background X‐ray counts are registered. There is no significant current through the aircraft, only brief 20 μs pulses synchronously with the corresponding EM pulse.
Figure 9
Figure 9
The second gamma ray glow. It starts at 07:42:00 and lasts for 30 s till 07:42:30 UTC. The vertical dashed lines are WWLLN and LIAS sferics. Some of them are numbered. Their locations are indicated in Figure 10. ILDAS was not triggered during this glow.
Figure 10
Figure 10
The WWLLN (squares) and LIAS (circles) spherics detected during second gamma ray glow. The WWLLN location uncertainty is shown as dashed oval around flash #2.
Figure 11
Figure 11
The spectrogram of the glow period binned in 1 s intervals. The first glow is visible at t = 270 s and the second at t = 650s. Two more spectra modifications can be seen after 800 s. Logarithmic number of particles is color coded. Energy channels are indicated on Y axis.
Figure 12
Figure 12
The measured spectrum of the first glow at its maximum compared to the background spectrum 10 s later. Dashed lines show power law fit dN/dE = N 0·E −λ. The spectral index λ for the glow is 1.8 and 1.3 for the background.
See this image and copyright information in PMC

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