Meteoroids as a source of metal ion clouds in Earth&rsquo;s upper thermosphere

Chen, Gang; Xu, Yimeng; Yang, Guotao; Feng, Wuhu; Xu, Jiyao; Zhang, Shaodong; Li, Guozhu; Fang, Hanxian; Du, Lifang; Zheng, Haoran; Cheng, Xuewu; Li, Faquan; Xun, Yuchang; Huang, Kaiming; Yan, Chunxiao

doi:10.5194/egusphere-2026-2356

Preprints

https://doi.org/10.5194/egusphere-2026-2356

Preprints

30 Apr 2026

| 30 Apr 2026

Meteoroids as a source of metal ion clouds in Earth’s upper thermosphere

Gang Chen, Yimeng Xu, Guotao Yang, Wuhu Feng, Jiyao Xu, Shaodong Zhang, Guozhu Li, Hanxian Fang, Lifang Du, Haoran Zheng, Xuewu Cheng, Faquan Li, Yuchang Xun, Kaiming Huang, and Chunxiao Yan

Abstract. Advances in lidar technology have enabled the detection of Metal Ion Clouds (MICs) at altitudes between 120–300 km in the Earth’s thermosphere. Observations from a Ca⁺ lidar in Beijing, China, reveal that these MICs are characterized by tightly packed, stripe-like structures that span extensive areas, covering hundreds to thousands of square kilometers. Some of these stripes extend downward to the Main Metal Layer (MML) around 100 km, and some clouds descend with tidal winds and merge into the underlying MML. While arriving the altitudes of Mesosphere and Low-Thermosphere (MLT), they lead to an increase in Sporadic-E (Es) layer density, and even trigger the formation of a new Es layer. The metal ions in the upper thermosphere will eventually sink into the MML and significantly affect its density variations. The striped structure of MICs and their direct effects on Es and MML suggest they originate from meteoroid trails, challenging traditional views on meteoric input.

Received: 24 Apr 2026 – Discussion started: 30 Apr 2026

Competing interests: The contact author has declared that none of the authors has any competing interests.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.

Download & links

Gang Chen, Yimeng Xu, Guotao Yang, Wuhu Feng, Jiyao Xu, Shaodong Zhang, Guozhu Li, Hanxian Fang, Lifang Du, Haoran Zheng, Xuewu Cheng, Faquan Li, Yuchang Xun, Kaiming Huang, and Chunxiao Yan

Status: final response (author comments only)

RC1:
'Comment on egusphere-2026-2356', Robin Wing, 01 Jun 2026
Review: Meteoroids as a source of metal ion clouds in Earth’s upper thermosphere
The authors present an excellent, high-quality, set of Ca+ observations from the lidar in Beijing. They note several cases where interesting vertical structures in the Ca+ measurements extend upwards from the main metal layer (MML) and suggest that these stripes could be due to meteor trails. The authors support their theory with observations of Total electron content from a co-located ionosonde and horizontal wind measurements at 250 km from an FPI.
I share the author’s interest in these fine layered features shown in the manuscript. They are a very peculiar structures which hints at some very complex underlying physics and definitely worthy of more study. Unfortunately, I think it unlikely that these vertical stripes are the results of meteor trails. More quantitative analysis is required to make a strong case.

A Case Against Meteor Trails:
In Figure 5 we see very high Ca+ (~10 cm-3) densities all the way up to 270 km. The plume containing these ions is very large lasting for many minutes. The amount of Ca atoms which must have come off the meteor would need to be very large to generate this signal over such a long observation time. The injection rate at 270 km must be many orders of magnitude higher than what we expect (i.e. Vondrak et al. 2008).
Sputtering likely occurs at 270 km based on observations of meteors but it may not be a sufficiently efficient mechanism for enough Ca injection to account for the measured values at 270 km. The atmospheric density is just too low, there are so few collisions that it would be difficult to justify the required Ca injection rate. Maybe below 150 km for very fast, small meteors this might work (but would they produce enough Ca to be detectable from ground???). Below 120 km likely already transitioning into normal ablation processes. (i.e. Hill et al. 2005). I would recommend that the authors do the calculations to see how much sputtering would be required to reproduce the observed Ca+ plume.

3D structure of the Ca+ plume and observed duration. The vertical streaks were seen for several minutes in the lidar. If this were a meteor trail from a small, fast meteor we have to assume that there is some diffusion and mixing. This means that the initial Ca+ plume density would be much higher immediately following ablation than the observed, diffuse plume. This would require an even larger Ca injection rate at the meteor trail which becomes harder to support.

Alternative mechanisms exist which could produce very narrow, nearly vertical structures in the ionosphere. These should be excluded (as much as possible).
Field-aligned ion structures could correspond to a perturbed ionosphere. I would check the local magnetic field inclination measurements projected to the lidar field of view.

Upward advection of Ca from the MML and transport/concentration of Ca+ into thin layers. This would be my first guess whenever I see large, dense structures in the thermosphere. This could be difficult to investigate without winds at the topside of the MML. Perhaps asking nearby radar if they can estimate bulk wind at these altitudes?

Es and sporadic Ca+ coupling could be possible. Figure 4 makes this connection. I would be careful trying to work out the direction of causation (Es àCa+ vs Ca+ à Es). But one could imagine a situation where very local ionospheric irregularities make some very interesting metallic ion convergence patterns.

E x B drift of Ca+ structures from outside the lidar field of view. We do not know what the Ca+ cloud looks like before observations. It is a huge, 3D extended structure interacting with an unknown electric and magnetic field. How theses Ca+ structures look in 1D when passing over a very narrow lidar field of view can be challenging to interpret. I would differentiate this from point a) in that there could be smaller “sub-gridscale” irregularities in the ExB which impact the observed ions in complex ways.

Auroral activity has been shown to create local ionization and influence metal ions (i.e. Chu 2020). This should be excluded as a possibility.

Neutral dynamics and Gravity Waves can also distort what we see in the lidar. We only know the wind at one altitude at low measurement resolution. We are unable to know what local vertical and horizontal wind shears can be occurring due to waves. Depending of the shears, a Gravity wave could concentrate some ions into a layered structure with a normal intrinsic propagation phase speed. Then depending on the relation between the gravity wave phase speed and the background wind (plus wind shear) the observed phase lines (and Ca+ structures) can have nearly any possible orientation.

Minor points:
L38: I suggest: “When meteoroids and space debris…” space debris is becoming significant and a topic of interest
L46: replace “non-metal species” with a more specific list.
Figure 2: matching the time between the lidar and Ionosonde for each measurement makes it easier for the reader to follow.
L136-137: Be careful of making causation statements. The physics is complex such statements should be strongly supported.
L137-139: A quantitative would be more convincing.
L139-140: All data access statements can be put at the end in the Data Availability Section.
L148: A quantitative timeseries analysis would be stronger proof.
L151: Good to keep in mind that these structures are very larger with complicated (and unknown) 3D shapes.
L154-155: Yes, a quantitative analysis would strengthen this point.
Figure 3: This figure is quite complex. It took me several minutes to completely understand what was happening. I would suggest reducing the complexity. Perhaps one case per figure?
L198-200: Be careful with correlation and causation. To make the case for causation I would prefer to see more quantitative analysis.
Figure 5: Don’t overinterpret the small bend in the MSIS density curve. MSIS semi-empirical, climatological model. It can’t be expected to accurately show the state of the atmosphere in real time.
L246-247: The change I density scale height is not really large enough to create a big difference in the ablation. The absolute density is the important thing. The formation of the MMLs has much more to do with the chemistry than the density. The framing of the MML formation is a bit strange here. See any paper by Plane et al.
General comment:
The structure of the paper presenting multiple cases is a bit difficult to follow. I would consider restructuring how case studies are presented to make it easier for a reader to quickly see the points you want to make.

Vondrak, T., Plane, J. M. C., Broadley, S., and Janches, D.: A chemical model of meteoric ablation, Atmos. Chem. Phys., 8, 7015–7031, https://doi.org/10.5194/acp-8-7015-2008, 2008.
Hill, K.A., Rogers, L.A. & Hawkes, R.L. Sputtering and high altitude meteors. Earth Moon Planet 95, 403–412 (2004). https://doi.org/10.1007/s11038-005-9018-x
Chu, X., Nishimura, Y., Xu, Z., Yu, Z., Plane, J. M. C., Gardner, C. S., & Ogawa, Y. (2020). First simultaneous lidar observations of thermosphere- ionosphere Fe and Na (TIFe and TINa) layers at McMurdo (77.84°S, 166.67°E), Antarctica with concurrent measurements of aurora activity, enhanced ionization layers, and converging electric field. Geophysical Research Letters, 47, e2020GL090181. https://doi.org/10.1029/2020GL090181
Citation: https://doi.org/10.5194/egusphere-2026-2356-RC1
RC2:
'Comment on egusphere-2026-2356', Anonymous Referee #2, 06 Aug 2026
Review comments on “Meteoroids as a source of metal ion clouds in Earth’s upper thermosphere” by Chen et al. to ACP
The lidar observational data of Ca+ ion layers from Beijing used in this manuscript are not new because the major cases have been reported and discussed by Jiao et al. (2022) as the thermosphere-ionosphere Ca+ (TICa+) layers. Later, Jiao et al. (2026) published a statistical study of TICa+ data from Beijing. The Beijing lidar data of Ca+ ions are very valuable and have provided new opportunities for the science community to study and understand the midlatitude ionosphere and its coupling with the thermosphere and mesosphere.
However, this current ACP manuscript ignored the detailed studies of TICa+ by Jiao and co-workers in critically peer-reviewed journal papers and of other thermosphere-ionosphere metal (TIMt) layers by many researchers, especially their arguments in those papers why meteoroids could not be the direct source of these TICa+ and other TIMt layers. Consequently, this manuscript proposed a new explanation, based on speculations and misunderstanding of many aspects of metal layer and meteor studies, which was basically against first-principle studies of meteoroid sputtering and ablation by Plane and co-workers as well as many other researchers over decades. The picture/explanation described in its abstract and main text is wrong, opposite to the observational facts and numerical modeling results by various researchers over many decades. Therefore, this paper should be rejected completely.
Below we provide some details for several major points --
The major error and misunderstanding in this manuscript lie in sputtering and ablation of meteoroids, the resultant injection rates of metals & their altitude distribution. By now it is a common knowledge in the science field that the injection rates of metals (including Fe, Na, Ca, Al, Ti, K, Mg, Si, Ni) from meteoroids above 120 km are negligible due to the Earth’s atmosphere low densities and it is impossible to form the densities of metal ions and metal atoms observed by lidars. Let’s quote the following text from Chu and Yu (2017) –

“To provide a quantitative concept, we take the latest calculation results from Carrillo-Sanchez et al. (2016), which give the Fe injection rates of about 1.7x10^-5, 3.2x10^-6, 4.7x10^-7, and 5.0x10^-8 cm^-3s^-1 at respectively 125, 150, 200, and 300 km for the Planck distribution. Then we compute the average Fe densities for 1 day of continuous accumulation without any loss by downward transport. … The resulting absolute Fe densities are respectively 1.5, 0.28, 0.04, and 0.004 cm^-3at these four altitudes.” – Note that such Fe densities are at least two orders of magnitude smaller than Fe lidar observations (Chu et al., 2011).
According to Carrillo-Sanchez et al. (2020) (see their Figure 3), the injection rate of Ca is even 1-2 orders of magnitude smaller than that of Fe because Ca is a minor species when compared to the major metal species of Fe, Mg, and Si. Thus, direct meteoroids’ sputtering and ablation is an impossible path to produce Ca+ ions with lidar-observed densities from 120-300 km.
Worth noting that studies of meteoroid sputtering and ablation have been ongoing for decades by many researchers. Plane (2026) summarizes how the metal injection rate profiles were derived from the first-principle model CABMOD that integrates laboratory simulations and an astronomical dust model. Because of such solid history, the science community understands that meteoroids cannot be a direct source to the lidar-observed Ca+ ion layers that exhibit obvious vertical motions with various periods.
The lidar-observed TICa+ layers over Beijing are intriguing and challenging the community’s understanding on ion transport and layer formation. Authors had a good intention of trying to advance the understanding via proposing an explanation different from the mainstream. However, their meteoroid explanation as proposed in the manuscript is baseless. Some of their reasons are caused by some misunderstanding of metal layers’ transport. For example, metal layers’ transport is three dimensional (3-D), so horizontal transport should be considered. For a single lidar beam vertically pointing, horizontal transport can cause advection of TICa+ metal layers (formed from other locations) to pass over the lidar team, leading to some Ca+ layers (like Figure 1a) that have no connection to the main layers.

Regional vertical ion transport is still possible as demonstrated in Chu and Yu (2017) for Antarctica and discussed by Jiao et al. (2022) and Chu et al. (2021) for midlatitudes, although many more studies are needed to get to the bottom of the mechanisms. We strongly encourage authors to study those papers and numerous papers cited there, including various modeling papers and observations.

These papers have established a self-consistent picture that the meteoroids mainly deposit metals to the main deposition region (~80-115 km), including both neutral metals and metal ions. Driven by electric fields and neutral winds, the metal ions can be transported upward to several hundreds of kilometers (see Figures in Chu & Yu (2017)) and then descend and are converged by neutral wind shears under geomagnetic fields to form metal ion layers, i.e., TIMt+ layers, such as TICa+ layers. Neutralization of these converged metal ion layers can produce neutral TIMt layers. The metal ion transport by neutral winds and electric fields can form sporadic E layers in both the upward and downward transport processes.

Although the midlatitude electric fields are in general smaller than the polar and equatorial regions, there are several mechanisms that may enhance the E-fields as discussed in Jiao et al. (2022) and papers cited there. These mechanisms include at least sporadic E layers and gravity waves. We encourage authors to study those papers and perhaps make progress.

Quite some features in the TICa+ shown in Figure 1 of this manuscript and in Jiao et al. (2022, 2026) have clearly suggested vertical (and horizontal) ion transport from the main deposition layer region to several 100s km and vice versa. Figures 1b, 1c, and 1d were discussed in Jiao et al. (2022) showing repeated up and down transport with connections to the main layers. Such features cannot be caused by meteoroids but by dynamical/electrodynamical processes in the ionosphere-thermosphere region, such as neutral winds, electric fields, and gravity waves along with the interactions between the F region and the sporadic E layers. Additionally, Jiao et al. (2026) reported “dawn” type TICa+ layers to 180 km, which correspond to the predawn TINa layers observed over Boulder (also a midlatitude site) by Chu et al. (2021) and Chu and Chen (2025). These predawn or dawn-type metal layers occur regularly (basically every day) before the sunrise. Meteoroids cannot have such regular occurrence.

Worth noting that the Beijing lidar data of TICa+ were taken with a Ca+ lidar who frequency wasn’t locked. Sometimes the laser frequency might drift or fluctuate, which could cause vertical stripes in Ca+ density data.Jiao et al. (2026) presented a detailed discussion about this point, although the case in their Figure 7 ruled out the laser frequency drift.

References used in the review comments –
Carrillo-Sánchez, J. D., Gómez-Martín, J. C., Bones, D. L., Nesvorný, D., Pokorný, P., Benna, M., Flynn, G. J., & Plane, J. M. C. (2020). Cosmic dust fluxes in the atmospheres of Earth, Mars, and Venus. Icarus, 335, 113395. https://doi.org/10.1016/j.icarus.2019.113395

Carrillo-Sánchez, J. D., Nesvorný, D., Pokorný, P., Janches, D., & Plane, J. M. C. (2016). Sources of cosmic dust in the Earth's atmosphere. Geophysical Research Letters, 43, 11979–11986. https://doi.org/10.1002/2016GL071697

Chu, X., Yu, Z., Gardner, C. S., Chen, C., & Fong, W. (2011). Lidar observations of neutral Fe layers and fast gravity waves in the thermosphere (110–155 km) at McMurdo (77.8°S, 166.7°E), Antarctica. Geophysical Research Letters, 38(23), L23807. https://doi.org/10.1029/2011GL050016

Chu, X., & Yu, Z. (2017). Formation mechanisms of neutral Fe layers in the thermosphere at Antarctica studied with a thermosphere-ionosphere Fe/Fe+ (TIFe) model. Journal of Geophysical Research: Space Physics, 122(6), 6812–6848. https://doi.org/10.1002/2016JA023773

Chu, X., Chen, Y., Cullens, C. Y., Yu, Z., Xu, Z., Zhang, S., Huang, W., Jandreau, J., Immel, T. J., & Richmond, A. D. (2021). Midlatitude thermosphere–ionosphere Na (TINa) layers observed with high-sensitivity Na Doppler lidar over Boulder (40.13°N, 105.24°W). Geophysical Research Letters, 48(11), 1–10. https://doi.org/10.1029/2021GL093729

Chu, X., & Chen, Y. (2025). Lidar discovery of annual and semiannual oscillations of thermosphere-ionosphere Na (TINa) layers and the first Na climatology of 75–150 km: Connections to metallic ions, wave and eddy transport, and meteoric influx. Geophysical Research Letters, 52, e2025GL117844. https://doi.org/10.1029/2025GL117844

Jiao, J., Chu, X., Jin, H., Wang, Z., Xun, Y., Du, L., Zheng, H., Wu, F., Xu, J., Yuan, W., Yan, C., Wang, J., & Yang, G. (2022). First lidar profiling of meteoric Ca+ ion transport from ~80 to 300 km in the midlatitude nighttime ionosphere. Geophysical Research Letters, 49(18), e2022GL100537. https://doi.org/10.1029/2022GL100537

Jiao, J., Jia, H., & Xun, Y. (2026). Lidar observations of thermosphere‐ionospheric Ca+ at Beijing (116.02E, 40.42N), China. Journal of Geophysical Research: Space Physics, 131, e2025JA034560. https://doi.org/10.1029/2025JA034560

Plane, J. M. C. (2026). Mesospheric-Metal layers. In Reference Module in Earth Systems and Environmental Sciences. Elsevier. https://doi.org/10.1016/B978-0-323-96026-7.00013-8
Citation: https://doi.org/10.5194/egusphere-2026-2356-RC2
EC1: 'Comment on egusphere-2026-2356', Peter Haynes, 07 Aug 2026

Writing as Editor responsible for this paper, I regret that it has taken a long time to obtain two reviews of your paper. However, now that we have two independent reviews, I see that both reviewers are skeptical of your hypothesis that the observed structures originate from meteoroid trails.
Referee 1: 'Unfortunately, I think it unlikely that these vertical stripes are the results of meteor trails. More quantitative analysis is required to make a strong case.'
Referee 2: 'However, this current ACP manuscript ignored the detailed studies ... thermosphere-ionosphere metal (TIMt) layers by many researchers, especially their arguments in those papers why meteoroids could not be the direct source of these TICa+ and other TIMt layers.'
Your abstract notes that your hypothesis challenges traditional views on meteoric input -- and of course it is always interesting when traditional views are challenged -- but my impression from the reports is that the reviewers do not find your arguments in support of the hypothesis convincing and that significantly more work would be needed to change this situation.
The ACP procedure is that it is up to you -- the authors -- to decide whether to submit a revised manuscript. However, my impression is that the changes that would be required to your manuscript to make it convincing to referees are very substantial and my initial advice is that it may be better, in due course, to submit a new manuscript including new evidence and arguments, rather than attempting to revise the current manuscript.
I will be happy to discuss this further by email if you wish.

Citation: https://doi.org/10.5194/egusphere-2026-2356-EC1

Gang Chen, Yimeng Xu, Guotao Yang, Wuhu Feng, Jiyao Xu, Shaodong Zhang, Guozhu Li, Hanxian Fang, Lifang Du, Haoran Zheng, Xuewu Cheng, Faquan Li, Yuchang Xun, Kaiming Huang, and Chunxiao Yan

Viewed

Total article views: 480 (including HTML, PDF, and XML)

HTML	PDF	XML	Total	BibTeX	EndNote
365	72	43	480	33	41

HTML: 365
PDF: 72
XML: 43
Total: 480
BibTeX: 33
EndNote: 41

Views and downloads (calculated since 30 Apr 2026)

Month	HTML	PDF	XML	Total
Apr 2026	31	8	2	41
May 2026	259	34	17	310
Jun 2026	31	6	5	42
Jul 2026	27	18	4	49
Aug 2026	17	6	15	38

Cumulative views and downloads (calculated since 30 Apr 2026)

Month	HTML	PDF	XML	Total
Apr 2026	31	8	2	41
May 2026	259	34	17	310
Jun 2026	31	6	5	42
Jul 2026	27	18	4	49
Aug 2026	17	6	15	38

Viewed (geographical distribution)

Total article views: 461 (including HTML, PDF, and XML) Thereof 461 with geography defined and 0 with unknown origin.

Country	#	Views	%

Latest update: 09 Aug 2026

Short summary

A new lidar for calcium ion (Ca⁺) observations has been operated in Yanqing, Beijing, China. Cloud-like Ca⁺ are observed to occur at altitudes of 120–300 km, and these clouds are composed of striped structures. These Ca⁺ are found to descend into Es layer and the main metal layer, and increase their ion density. According to the stripe-like structures and their influence on the metal ion layers, we believe that these metal ions observed by the lidar in Beijing come from meteoroids trails


Total:	0
HTML:	0
PDF:	0
XML:	0