the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 30 Jun 2026
Thermospheric shock waves and lensing of light in the Barium Release, Optical and Radio rocket experiment
Abstract. The Barium Release, Optical and Radio (BROR) rocket experiment, launched from Esrange near Kiruna, Sweden, involved eight releases of barium at different altitudes in the thermosphere to study electric fields near small scale auroral structures. The barium was ejected into the thermosphere by the explosion-like combustion of ignited copper oxide thermite. Shock waves could be observed optically from the ground to follow the barium ejections when the rocket speed was supersonic, but not when it was subsonic. The shock waves are attributed to copper droplets that resulted from the thermite combustion and other particulate matter in the ejecta that traveled at supersonic speed. The observed deceleration of the shock waves can be explained by frictional drag together with gravity on copper droplets having a mean radius of about 1 mm. The actual observation of the shock waves from the ground is attributed to scattering of sunlight on the particulate matter in the ejecta. Also, following the ejections at the highest speeds, optical lensing of sunlight reflected from the rocket itself was observed, in that the rocket appeared brighter just after the barium release than before the release.
- Preprint
(1091 KB) - Metadata XML
- BibTeX
- EndNote
Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-2925', Navin Parihar, 20 Aug 2026
-
RC2: 'Review report and comments on egusphere-2026-2925 "Thermospheric shock waves and lensing of light in the Barium Release, Optical and Radio rocket experiment"', Anonymous Referee #2, 23 Aug 2026
This manuscript can be considered a derivative work based on the BROR (Barium Release, Optical and Radio rocket) experiment. As the main objective of the experiment is to understand the electrodynamics of the auroral region under geomagnetic storm conditions; the present manuscript focuses on a secondary and unforeseen phenomenon: the shock waves observed as a result of several barium ejections. The unique conditions of the experimental setup certainly made it possible to reveal the shock waves associated with these barium ejections; as this is a phenomenon that has received little discussion, it lends scientific merit to the manuscript.
The decision to divide the document into Introduction, Observations, Discussions and Conclusions (it is more of a Summary section than a Conclusion section) is correct, although I recommend making the Discussions section an independent section (section 3) instead of the current one 2.1. The organization and presentation of the content are adequate and exhibit a sequence of reasoning that can be followed acceptably well.
Below I will list in detail the aspects that I detected and that need to be reviewed and improved along with questions that must be answered by the authors.Section Introduction:
Although the main results are presented in the paper by Taki et al., 2026, It is worth reinforcing the original purpose of the experiment. Highlight the relevance of barium-release experiments to study the MLT and ionosphere regions. Also the significance of this unusual detection of supersonic shock waves, and its potential interference with the interpretation of optical data from the barium cloud itself must be addressed (and further develop in the Conclusion section, which would truly do justice to the name, since in its current state it is more of a Summary of what was done/found).
Line 12: Especify UTC-LT difference e.g. (LT =UTC + 2) or (20:23:00 LT)
Line 24: What can be estimated? The intensity, the direction, or both properties of the electric field?
The most important change to be implemented is the following:
Line 40-42 It is recommended to insert a figure showing the rocket's trajectory, the position of the cameras, its FOV and the solar terminator during the launch time, with the geographical map in the backgroundSection Observations:
The placement of the figures negatively affects the smooth reading of the description of what was observed. There is a huge gap between the text on line 102 and its continuation on line 103, two pages later. Something similar occurs between the text on line 122 (page 7) and its continuation on line 123 (page 10). Some basic information regarding the rocket launch and the geomagnetic conditions during the execution of the experiment should be placed at the beginning of this section: duration of flight, numbers of rocket´s stages, time of stages burning, main and (if any) secondary payload, trajectory details, ballistic flight time, rocket rotation and precession frequency, and general geomagnetic condition during the experiment. The foregoing can be presented in a table form.
Figure 1 caption: Its not clear if this speed rocket profile is during upleg, downleg or the whole trajectory
Line 86 and 87: A cartoon explaining how the barium is released respect the rocket body could shed light on the experimental set up. What was the rocket's rotational speed and how it may have influenced the release of the barium and the remnants of the thermite?
Line 96: "Figure 6a depicts the light intensity (black) along the direction of the rocket velocity a few seconds..." It´s possible to include this direction overlapped in one of the panel in Figure 2? This would clarify for the reader in which part of the figure (anywhere from 2 to 5) the pixel count shown in Figure 6a was performed.
Line 98: What is the temporal resolution of the camera? If is a video, then what is the FPS?. This could have been clarified at the beginning of this section, along with the rocket's characteristics.
Line 105 and 106: Better express the Cs1,2,3 in m/s instead of km/s. The horizontal axis in Fig 1 is in m/s and in the rest of the text, the velocities are expressed in m/s.
Line 107: This second part of the sentences needs to be improved
Line 118: While it is true that u1f > u1, the fact that it is enclosed in parentheses indicates to the reader that this relationship is a consequence of the immediately preceding argument: "shock maximum decelerated slightly faster than the shock front" and this cannot always be the case, since du1/dt > du1f/dt does not imply u1f > u1. Better remove the "(u1f > u1)" because is already informed in Figure 7.
Line 147 and 148:The comment made in lines 40-42 can be applied to clarify this last comment.Section Discussion: Although this part is the most successful and coherent, I have two concerns, especially the one related to the determination of r (equation 14)
Line 185 (last part): Are you implicitly assuming that the direction of the vertical wind in the thermosphere (~200 km) for a high latitude (~68 deg N), near the equinox and around sunset is upward? If yes. You must show which model or previous empirical result confirms that statement. Hint: During that day Earth was struck by a severe G4-class geomagnetic storm.
Line 196, 198, 199, 225 to 227: Replace kg/m/s for the correct I.S. unit kg/(m . s)
Line 203: The comment made on lines 86 and 87 applies here as well.
Line 235 and first half of 236: Based on [7] and [10], the viscous friction force—and consequently the deceleration—is proportional to *r* (the size of the Cu droplets); therefore, one would expect that the larger the droplet, the greater the viscous friction it experiences and the greater the deceleration. From Figure 9, it can be observed that the shock front does not undergo deceleration like the main part of the shock; this may be because the shock front is composed of smaller Cu droplets and, consequently, experiences less deceleration due to viscous drag. What I gathered from what was stated in this lines was exactly the opposite.
Line 236 (second half) and 237 Additionally, it is unclear which part of the shock is being referred to by the second half of Line 236 and the first half of line 237.
Line 243 (equation 14): The purpose of the text between lines 240 and 249 is to demonstrate that the Reynolds number is much less than 1. The calculated values of the copper droplet radius are used for this purpose. This radius was calculated by comparing experimental values—specifically acceleration, initial velocity, and the angle between the rocket's trajectory and the vertical—with the theoretical value expressed in Equation 12. In turn, to arrive at the expression in (12), it is presumed that the frictional force was accurately described by Stokes' law, which assumes a low Reynolds number (to be checked later on).
The Reynolds number in 14 depends on experimental values except for r, which was calculated in a way that assumes a small Reynolds number. I see a circular bias here, and I would like to better understand the reasoning applied in this case. I would expect the determination of the Reynolds number not to depend on a quantity (r) that—in order to be calculated/estimated—assumes a small value for the very number it helps to determine.
Line 288 and 289: I believe the angle formed between the rocket body and the incident sunlight should also be taken into account when determining whether or not it plays a role in the effect under discussion. Upon watching the video available on YouTube, I noticed that there is no significant variation in lighting during the flight. Still I recommend insert a figure showing the rocket's trajectory, the position of the cameras, its FOV and the solar terminator during the launch time, with the geographical map in the background. This will help the reader understand how the rocket's trajectory—relative to the position of the sun—might have influenced the effect discussed in this last paragraph.Section Conclusion: My main concert here is that given the content of this version, the section cannot strictly be considered a set of conclusions; rather, it is better viewed as a summary description of the work carried out in the preceding sections. There are aspects that could rightly be called conclusions, such as the hypotheses that may arise from the fact that ejection speed decrease with increasing altitude and the consequences for future experiments of Barium release using thermite given that shock wave from a release propagated in the wake of the preceding shock wave. This could not affect the experiment in the sense that a barium cloud will no longer propagate in a common thermosphere (the object of study) but will propagate in an environment affected by a previous ejection?
These aspects were not addressed and diminish the potential scientific impact this study could generate.Citation: https://doi.org/10.5194/egusphere-2026-2925-RC2
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 41 | 14 | 8 | 63 | 7 | 9 |
- HTML: 41
- PDF: 14
- XML: 8
- Total: 63
- BibTeX: 7
- EndNote: 9
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
Review Report for the manuscript "Thermospheric shock waves and lensing of light in the Barium Release, Optical and Radio rocket experiment", by Leyser et al.
General Comments:
Manuscript presents Barium Release, Optical and Radio rocket (BROR) experiment carried out over Esrange near Kiruna, Sweden. As an active and rare experiment, this study has high scientific merit, warrants publication and I am strongly in favour of its publication. However, major concern is poor organization of this submission and is not as per Annales Geophysicae format/guidelines. Owing to this manuscript, in its present form, is difficult to follow in terms of logical sequencing and readability. Overall, my recommendation is “Major Revision”; however, the below-mentioned major shortcomings need to be addressed.
Restructuring and reorganization of the manuscript should be done (as suggested below) to improve overall readability and logical flow:
1. Introduction Section:
Significance of barium-release experiments to study the mesosphere-lower thermosphere and ionosphere. Why? A brief overview of previous reports, and their limitations. Following latest works are missing and should be included.
a. Fletcher, A. C., Crabtree, C., Ganguli, G., Siefring, C., Soto-Chavez, A. R., & Netwall, C. (2023). Rocket-released neutral clouds in the ionosphere: Formation, evolution, and detection. Journal of Geophysical Research: Space Physics, 128, e2022JA031039. https://doi.org/10.1029/2022JA031039
b. Zhu, X., Hu, Y., Zhao, Z., Ni, B., & Zhang, Y. (2020). Ionospheric disturbance caused by artificial plasma clouds under different release conditions. Earth, Planets and Space, 72(1), 183. https://doi.org/10.1186/s40623-020-01317-9
Scientific objectives/Motivation of the BROR experiment, brief introduction about thermospheric shock, etc..
2. An overview of BROR experiment
Section should include location, launch date, time and duration of flight, payload(s), rocket trajectory, information on release characteristics, and location of optical cameras/details of other ground-based experiments, brief information of solar elevation, solar activity and geomagnetic conditions, etc.. Figure 01 is reasonable; however, should by preceded by a map showing Rocket trajectory. Release characteristics can be furnished in tabular format.
3. Methodology
3.1 Derivation of the speed of shock waves
3.2 Derivation of the radius of copper droplet
For each measurement, a typical example (showing best results) should be presented.
4. Observations and results
In this section, sub-sections devoted to each release should be presented individually covering shock waves observations and different measurements. Wherever possible, imaging observations should also be presented, and comparison with earlier measurements should be performed.
5. Discussion
Please highlight key observations, and dynamics/electrodynamics involved.
6. Summary and Conclusions
Summarize BROR experiment, key findings, limitations, etc.
“Data Availability” should be corrected to clearly mention if data used in this study is publicly available or restricted or mention contact (subject to Annales Geophyiscae policy).