the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 25 Nov 2024
First Reported Detection of a Winter Continental Gamma-Ray Glow in Europe
Abstract. This study presents the first-ever detection of a winter continental gamma-ray glow in Central Europe, observed during a rare winter thunderstorm on Milešovka hill, Czechia. Unlike typical gamma-ray glow events, which are usually linked to significant electric field increases, this unique observation reveals that no substantial electric field change was recorded during the glow, challenging existing models of thunderstorm-related radiation. The event was captured using a combination of advanced instruments, including a Ka-band cloud profiler and a high-energy gamma-ray spectrometer, which enabled detailed analysis of the storm's microphysics. The radar data indicated the alignment of ice crystals within the cloud, strongly suggesting the presence of a substantial electric field, despite its weak measurement on the surface. This unexpected decoupling of electric field strength and gamma-ray glow generation opens new avenues for understanding the processes driving high-energy phenomena in thunderstorms. The findings offer valuable insights into winter thunderstorm dynamics in continental climates, with broader implications for the study of high-energy atmospheric physics.
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RC1: 'Comment on egusphere-2024-3075', Anonymous Referee #1, 03 Dec 2024
General (major) comments
This is an intriguing paper that claims to have captured the first gamma-ray glow in Europe during the winter season.
The paper discusses the relationship between the gamma-ray glow and other observations, such as rainfall, electric fields,
and radio waves. I believe this work will be of significant interest to specialists in the relevant field.
However, there are some unclear points that may need clarification or correction. Please consider my comments below.[1] It would help the reader's understanding if the authors could explain why gamma-ray glows have not been observed
in the Europe continent during the winter until now. What made it possible to observe one this time?
Was it due to specific meteorological conditions, or had there simply been no prior observations conducted in winter?[2] Does the situation where the cloud base is below the observation station imply that the station is within the cloud?
Additionally, since the cloud base can be determined through a simple calculation if the temperature and dew point are known,
I wonder if this approach has been attempted. Furthermore, what is the measurement error of the ceilometer?
Even when accounting for this error, can it be conclusively stated that the cloud base was below the observatory?
Based on these considerations, please justify the claim that the glow was detected when the clouds were below.[3] L99 "This could be due to some frost on
the electric field mill and its location close to vegetation (trees are in close vicinity of the electric field mill)."
Is this true for this observation?
The authors also mention that there are several lightning discharges occurring before the glow around L104-L112, but there are no electric field variations related to them at all, right? If so, doesn't those mean that the electric-field mill data is unreliable for this entire observation? Please explain this thoroughly, as it pertains to the basis of the paper that there were no electric field fluctuations in this area, but gamma ray glow was observed.Specific (minor) comments
[1]Could the author please include the difference between Czech time and Universal Standard Time (UTC) somewhere,
so that the local time can be clearly understood?[2] I am uncertain which of the lightning discharges mentioned around L104–L112 correspond to Figure 2. Could the authors
please clarify this association more clearly?[3] Figure 1: Could the authors please explain the meaning of the light and dark gray shaded areas in the caption?
[4] Figure 2: The authors mention that the color scale represents the time since the first lightning,
but the relationship between the color change and the passage of time is unclear.
Could you please clarify this relationship?[5] Figure 3: Would it be possible to indicate the ranges for low-intensity gamma-ray glows and high-intensity gamma-ray glows directly on this figure?
[6] Figure 4: Could you please describe in the text the difference between high-intensity gamma-ray glows and
low-intensity gamma-ray glows？Also, is it possible to deduce the structure (length and/or width) of the electric field
in the direction in which electrons are accelerated toward the ground?
If such a deduction is possible, including this information would be beneficial for the reader.
[7] Although the percentage of the observed increase is stated, the actual statistical significance is unclear because the error is not shown in Figure 3. Could you please include the error in the counts in Figure 3?[8] 3.4.1 Spectrum: Is the spectrum shown here for the strong gamma-ray glow? If so, is it possible to derive a separate spectrum
for the weak gamma-ray glow? According to Figure 7, the weak gamma-ray glow has a wider temporal range than the strong gamma-ray
glow. However, the spectra shown here seem to be taken from the weak gamma-ray glow region, possibly because the two are considered distinct.
Alternatively, could it be that the spectrum obtained does not change significantly even if the background (BG) is taken from an earlier time? I would appreciate clarification in the paper on how the strong and weak gamma-ray glows are separated and how the BG affects the
derived spectrum.
Additionally, Figure 4 refers to low-intensity and high-intensity gamma-ray glows, which I believe correspond to the weak and strong gamma-ray glows, respectively. Is this understanding correct? If so, it would be better to use consistent terminology throughout the paper to avoid confusion.[9] L126-L128: “LDR and RHO values (Figure 4) show that the height of the thundercloud reflecting back the signal was even smaller, reaching a height of only 2500 m and only 1500 m."
I understand the meaning of the last 2500 m from Figure 4, but I did not understand the meaning of the 1500 m.
Could you please add a brief explanation to your paper?[10] L130–L136: Around these lines, the terms low-intensity gamma-ray glow and high-intensity gamma-ray glow are introduced, but they have not been defined earlier in the text. Could the authors please explain how these terms are derived and provide clear definitions?
Additionally, please clarify whether these glows correspond to the weaker gamma-ray glow and strong gamma-ray glow mentioned later in the text. The lack of such descriptions makes the connection with Figure 5 unclear.[11]L148-149: "This could confirm the previous existence of an area of intensified electric field that aligned the ice crystals and also caused the gamma-ray glow observed on the ground." I am not well sure why this result indicates such a situation. Could you add a brief explanation in the text?
[12]L162-163: "The data acquisition stopped 3 seconds before the discharge". Why did the acquisition stop? Is this due to pile-up?
Technical corrections
[1] Figure 6: This figure does not appear to be referenced in the text.
If it is not essential, perhaps it should be removed. Alternatively, please revise the text to include a reference to it.Citation: https://doi.org/10.5194/egusphere-2024-3075-RC1 -
CC1: 'Comment on egusphere-2024-3075', Ivana Kolmasova, 29 Dec 2024
The authors present a unique observation of a gamma glow event occurring during a continental European winter storm. The gamma-ray data are combined with detailed meteorological data, making the study a valuable contribution that deserves publication in the ACP Journal.
However, the authors used the electric field mill data that I provided to them without informing me and despite my indication that I had trouble interpreting it. The possible causes of measurement errors that the authors mention in the manuscript were made up by them without any consultation with me. As their data provider I disagree with this false interpretation: the measurement errors that the authors invented are irrelevant for this data set.
These otherwise good measurements are hard to interpret if the field mill is inside a charged cloud. Unfortunately, this is most probably the case of the data presented in this paper. It is not appropriate to draw the strong conclusions stated in the paper based on the electric field mill data, which may be influenced by the presence of cloud particles. I recommend removing the electric field mill measurements and any conclusions based on them from the manuscript.
Additionally, the authors have misinterpreted the data from Blitzortung, incorrectly considering detections that are several microseconds apart, as separate discharges. Furthermore, they did not mention that the two discharges reported by Euclid were classified as relatively weak negative IC discharges.
I propose an alternative explanation for the observed abrupt gamma glow termination, based on a proper analysis of the data from the Euclid and Blitzortung lightning location networks. For my hypothesis, I used the lightning data provided by the authors along with the manuscript. Additionally, I requested a comment from J. Lapierre of the global ENTLN detection network (Zhu et al., 2017), https://www.earthnetworks.com/why-us/networks/lightning/.
The two discharges identified by Euclid were missing from the ENTLN-released data. It was found (private communication with J. Lapierre) that while individual ENTLN network stations detected both discharges, the location and peak current estimates were insufficiently precise to include these detections in the database. A manual analysis revealed that the stronger discharge was detected by numerous stations located up to 900 km away from the discharge and that the waveforms recorded at individual stations showed clearly identifiable sky waves. This suggests a high probability that the discharge made a ground contact. The estimated peak current was 13±9 kA. It was also found that the ground wave pulse rise time was approximately 3 to 5 times longer than what is typically observed for standard cloud-to-ground lightning and might indicate the occurrence of upward lighting (Romero et al., 2012).
The detections reported by Blitzortung did not correspond to separate lightning discharges, as close discharges cannot occur several microseconds apart. Instead, these detections were likely located pulses originating from the extension of leader channels or their side branches. The location of these detected pulses suggests that multiple discharge leaders may have propagated near the top of the mountain.
Given the above-mentioned facts (longer pulse rise time, presence of sky waves, the discharge location estimated by Euclid, and the location of pulses detected by Blitzortung) along with the observer's confirmation of both the light from the discharge and the thunder, I hypothesize that the gamma glow was terminated by an upward-going lightning stroke initiated at the observatory tower (Wang et al., 2008; Zhou et al., 2012). I further speculate that the field mill might not have been able to detect the field change, as it was likely trapped within the charged area at the bottom part of the thundercloud.
Ivana Kolmasova
References:
Romero, C., M. Paolone, F. Rachidi, M. Rubinstein, D. Pavanello and D. V. Giri (2012), A statistical analysis on the risetime of lightning current pulses in negative upward flashes measured at Säntis tower, International Conference on Lightning Protection (ICLP), Vienna, Austria, 2012, pp. 1-5, doi: 10.1109/ICLP.2012.6344272.
Wang, D., N. Takagi, T. Watanabe, H. Sakurano, and M. Hashimoto (2008), Observed characteristics of upward leaders that are initiated from a windmill and its lightning protection tower, Geophys. Res. Lett., 35, L02803, doi:10.1029/2007GL032136.
Zhou, H., G. Diendorfer, R. Thottappillil, H. Pichler, and M. Mair (2012), Measured current and close electric field changes associated with the initiation of upward lightning from a tall tower, J. Geophys. Res., 117, D08102, doi:10.1029/2011JD017269.
Zhu, Y., Rakov, V.A., Tran, M.D., Stock, M.G., Heckman, S., Liu, C., Sloop, C.D., Jordan, D.M. Uman, M.A. Caicedo, J.A. et al. (2017), Evaluation of ENTLN Performance Characteristics Based on the Ground Truth Natural and Rocket-Triggered Lightning Data Acquired in Florida. J. Geophys. Res. Atmos., 122, 9858–9866.
Citation: https://doi.org/10.5194/egusphere-2024-3075-CC1 -
RC2: 'Comment on egusphere-2024-3075', Yuuki Wada, 01 Jan 2025
This manuscript reports the first detection of a gamma-ray glow in continental winter. Winter thunderstorms develop in specific regions, such as the Mediterranean Sea, the Great Lakes, and the northern coast of Japan, and those in the other areas are quite rare. Gamma-ray glows are second-to-minute lasting radiation bursts associated with thunderstorms. Gamma-ray glows associated with winter thunderstorms have been reported from groups in Japan. As far as this reviewer knows, this is actually the first report of a winter gamma-ray glow in continental Europe. Therefore, this manuscript is potentially worth publication. However, a major revision is recommended before the decision.
The biggest issue is the electric field measurement. The authors claim that the gamma-ray glow occurred in a weak electric-field situation. However, the measurement is unreliable as the field mill did not detect the glow-terminating lightning discharge. The Boltek EFM-100 is sensitive to lightning discharges, and the detections of glow-associated discharges have been reported by Chilingarian et al., JGR Atmospheres, 2017, and Chilingarian et al., Atmospheric Research, 2020. The authors described that the Milesovka observatory reported a very close discharge associated with the glow. This reviewer cannot believe that the field mill did not detect the close lightning discharge. The authors should verify the time tagging of the data. If no anomaly is found, the result is unreliable unless the authors present a convincing reason. Then, the descriptions and discussions concerning the field-mill observation should be deleted because the conclusion somewhat contradicts the previous reports, and the authors must avoid a sensitive conclusion with an unreliable measurement.
The second issue is the structure of the manuscript. Because the main focus of this manuscript is gamma-ray glow, the authors should describe the feature of the gamma-ray glow first and then describe the meteorological condition and other measurements, such as the cloud profiler and the field mill. However, the Results section started with a description of the lightning discharge and the explanation for the glow itself was made later in the section. Especially the definition of strong and weak glows should be put earlier.
Detailed comments are listed below.
Abstract: please reconsider the statements on the field-mill observation.
L.13: Kelley et al. and Kochkin et al. are not the first reports of gamma-ray glows by airborne experiments.
L.14: The references should be placed right after the place name. Also, it would be better to include the country name along with the place name.
L.23: Does "peak" mean count rate or surface electric field?
L.26: Please remember that lightning discharges may also terminate MOS-origin glows.
L.42: Please add the unit to "0".
L.44: This paragraph is somewhat messy and should be rewritten. For example, time-over-threshold should be explained more. Also, statements of pileups and GPS time tagging should be separated.
L.48: This description is unclear. What is set for 4.5 MeV? According to the description, only below 4.5 MeV seems to be registered, which is not the case.
L.55: Please specify how to record the photons by SEVAN, event-by-event recording, or only count-rate recording.
L.61: Please explain how to calibrate the surface field measurement. Typically, it should correspond to 0.1 kV/m in fairweather.
L.64: Radar parameters should be explained more because the community of high-energy atmospheric physics is not usually familiar with radar meteorology. Also, the radar seems to work with alternate transmission and simultaneous reception mode as it can obtain LDR. It should be explained (not trivial for outside the radar community).
L.88: Figure 1 is not enough to determine the thunderstorm system. In fact, frontal systems are associated with a drop in temperature, but this is also the case for downbursts. The easiest way is to refer to radar observation and weather charts. Is the operational radar data available? If the authors would like to put a stress on meteorological conditions, these data are necessary.
L.90: A plot with a wider area than Figure 2 is needed to understand this paragraph. Also, flash rate is important (please be careful with the definition of flashes.)
Figure 2: This figure is somewhat meaningless. The colors should be the same for the two data sets. Also, a scale is needed to emphasize the distance between discharge points and the observatory. Also, please confirm the definition of flash. EUCLID and BLITZ only provide the source position of radio-frequency pulses, which often correspond to lightning currents (or strokes). A lightning flash is a collection of lightning currents.
L.93: The first thing to do here is to show the gamma-ray glow. Especially the presentation and definition of strong and weak glow should be put first. Otherwise, the discussion is quite missing and unclear.
L.98-99: This explanation is not convincing but connected to the main conclusion of this manuscript. Please consider removing or carefully verifying this.
Figure 3: There are several missing data for RT-56. This leads us to interpret it as unreliable. In fact, the discussion can be made only with the SEVAN data. Please reconsider whether RT-56 data is included or not. My feeling is that RT-56 should work without GPS signals. Also, please specify that the SEVAN data is non-coincidence or coincidence for the top layer.
L.110: Please confirm the definition of flash.
L.113: Please show the summary of Popova et al. if the analysis is essential for this manuscript.
L.114-121: Please entirely reconsider this paragraph.
L.125: Ka-band is very sensitive to attenuation in strong precipitation. In such cases, the measurement of cloud top height is quite challenging. Also, please show the actual value of cloud top height estimated by the geostationary satellite.
L.129: The definition of the low-intensity glow should be placed earlier.
L.135: Hail can be observed by the disdrometer. The result of the disdrometer should be referred to here.
L.137-149: This description should be placed earlier or the first of Section 3.
L.141: Please explain how to sense the vertically aligned ice crystals with LDR and RHOHV.
L.157: Please define "high-energy" photons.
L.161-163: This description should be explained more. Again, the discussion with RT-56 data seems to be unreliable.
L.174: What are the wind speed and cloud base information used for? Please be careful with the cloud base information because the ceilometer cannot measure it during heavy precipitation.
Figure 6: The intent of this diagram is unclear. Also, it would be better to unify the range of the vertical axis. Please explain solid precipitation and no hydrometer.
Figure 7: A more precise explanation of Gaussian fittings should be made in the main text. Also, how do we define the center time if a double Gaussian function is used for the fitting? Again, the discussion can be done without RT-56.
Figure 8: The high-energy part (>3 MeV) is not smooth, different from the previous report (Wada et al., PRR, 2021). Please explain why such a structure can be seen. Also, I have doubts about the accuracy of the energy above 4.5 MeV (determined by time-over-threshold). How to calibrate the high-energy domain?
L.187: My feeling is that this manuscript is just a case report rather than a scientific paper. Please take the comments above into account and include more discussions.Citation: https://doi.org/10.5194/egusphere-2024-3075-RC2
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