the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 11 Dec 2025
Studies of noctilucent clouds from the stratosphere during the 2024 TRANSAT balloon flight
Abstract. A transatlantic scientific balloon flight (TRANSAT) was conducted between 22 and 26 June 2024. The TRANSAT balloon, operated by the French Space Agency (CNES), floated in the stratosphere at approximately 40 km altitude between Esrange (Sweden) and Baffin Island (Canada) for about 3.8 days. The scientific payload comprised nine instruments, including two from the Swedish Institute of Space Physics: an optical imager for noctilucent cloud (NLC) studies and an infrasound instrument for atmospheric infrasound wave investigations. The NLC imager consisted of three identical visible-range optical cameras, one of which operated successfully throughout the entire flight, capturing thousands of NLC images. The TRANSAT balloon campaign was supported by ground-based lidar measurements and spaceborne observations from the Swedish MATS satellite. Here, we describe the technical characteristics of the balloon experiment and present early results. Nearly continuous observations of NLC were obtained during the entire flight. A localized warm region in the mesopause was identified as the cause of temporary NLC disappearance, while complex NLC structures exhibiting different motions were found to probably result from horizontal wind rotation with altitude within the mesopause region.
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Status: open (until 20 Feb 2026)
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RC1: 'Comment on egusphere-2025-5757', Anonymous Referee #1, 14 Jan 2026
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AC1: 'Reply on RC1', Peter Dalin, 22 Jan 2026
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We are grateful to the Reviewer 1 for reviewing our manuscript and for the useful comments that allowed us to improve the manuscript. Below are our responses to the Reviewer's comments marked in bold.
Specific Comments:
1. In Section 2.1, Sony α7 M3 is an SLR camera, and its operation is generally manual. It is suggested that the author add a description here to explain how to realize automatic shooting and how to transform the cameras.
This camera has a standard Micro USB terminal for power supplying, battery charging and USB communications, into which an external trigger can be connected to activate the shutter button. For this purpose, we have developed an external trigger (the gray box shown in Fig. 1) that simultaneously transmits the trigger signal to all three NLC cameras at a certain frequency (50 s in this experiment). Thus, automatic shooting is carried out by three cameras throughout the balloon flight. In addition, this external device distributes power to all three cameras from an external power supply (a chemical battery on the gondola). We have added this information to the revised manuscript.
2. I noticed that there are four different gaps in the observation of NLCs in Figure 5, and then I mapped the gap time to the flight location in Fig.2a. It seems that the regions where these gaps appear are not consistent with the warm regions in Fig.9. Can the author provide some explanations? In addition, I suggest marking the location and coverage of each gap in Fig. 2a or b.
We have added the locations of each gap (four gaps comprise 8 points) in Fig. 2a. The second gap does include the warm region shown in Fig. 9, taking into account the field of view of the camera projected on the Earth’s surface as shown in Fig. 8.
3. In Section 4.3, I downloaded and watched the video provided by the author carefully. I can see that the structures of NLCs have different directions of movement, but I am not sure whether it is a double-layer cloud, and whether it is just the change caused by gravity waves in different directions of propagation? Can the author provide some more detailed and convincing evidence and identification process for distinguishing double-layer clouds?
As we noted in Section 4.3, we cannot measure the heights of the NLC layers in this experiment. Therefore, we cannot 100% assert the presence of a double NLC layer in this case. The Reviewer 1 is partly right in this. At the same time, we showed that the double NLC layer was previously detected by the ALOMAR lidar in Norway. In addition, we have provided a list of theoretical and experimental studies showing the mechanism of formation of a double NLC layer and statistics on double and multiple layers in NLC. Thus, a double NLC layer is not such a rare phenomenon but it is formed relatively often.
Also, we analyzed this event based on JAWARA model data, which showed the presence of an inertia-gravity wave and the rotation/change of neutral wind with height, which is an inherent property of a gravity wave. There is good agreement between the measured NLC velocities and the model wind velocities. Therefore, it can be assumed with a high probability that there was the double NLC layer in this space-time domain, and the different NLC motions may be a consequence of the passage of this wave through the NLC layer.
Other potential explanations in this regard are speculative and cannot clarify the presence or absence of the double NLC layer. We want to avoid unnecessary speculative reasoning in the present manuscript.
4. I suggest that figure 6, figure 9 and figure 10 all indicate a, b, c, d….
We agree with this comment and have added abbreviations A, B, C, D of the panels in Figs. 6, 9 and 10.
Citation: https://doi.org/10.5194/egusphere-2025-5757-AC1
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AC1: 'Reply on RC1', Peter Dalin, 22 Jan 2026
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Review of " Studies of noctilucent clouds from the stratosphere during the 2024 TRANSAT balloon flight " by Peter Dalin et al.
General Comment:
The prime objective of this manuscript is to investigate the dynamics and variability of noctilucent clouds (NLC) through unprecedented stratospheric balloon-based imaging, supported by ground-based lidar and satellite observations. Key results from the comprehensive observations and multi-instrument analysis indicate that NLC were detected nearly continuously over 3.8 days, with their disappearance linked to a localized warm region in the mesopause caused by the intrusion of mid-latitude air. Furthermore, observed double-layer NLC structures moving in opposite directions were consistent with wind shear and inertial-gravity wave activity. Overall, most of the analysis in this manuscript is well executed and the conclusions are well-reasoned. However, the present manuscript has some shortcomings, and that is why the manuscript can be considered for publication after minor revisions from my point of view. I would like to give my comments below that need to be addressed.
Specific Comments: