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

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

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30 Apr 2026

| 30 Apr 2026

Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

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.

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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

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RC1:
'Comment on egusphere-2026-2356', Robin Wing, 01 Jun 2026 reply
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

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Citation: https://doi.org/10.5194/egusphere-2026-2356-RC1

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

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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


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