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
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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
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