the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 10 Jul 2026
On the Role of Atmospheric Waves in Governing the Persistence of Thin Cirrus Clouds in the Tropical Tropopause Layer
Abstract. Thin tropical cirrus clouds influence the radiative and stratospheric water vapor budgets, yet the processes controlling their persistence remain poorly constrained. Here, we investigate the impact of multiscale wave-driven vertical wind speed and temperature fluctuations on thin tropical cirrus lifetime using a Lagrangian microphysical model initialized from lidar observations obtained during the Strateole-2 campaigns. The model represents the evolution of ice crystal populations under stochastic high-frequency gravity wave forcing and an idealized low-frequency inertia gravity wave. Our results show that cirrus lifetime is controlled by a competition between stabilization through multiscale cooling fluctuations and complete sublimation by rare, high amplitude warming events due to gravity waves. This introduces a threshold behavior: if some ice crystals can grow large enough without being dissipated in the first hours of the lifetime, they become less sensitive to complete sublimation and enter a stabilization regime in which sedimentation determines the cloud lifetime. Stronger gravity-wave activity shifts this stabilization regime toward larger crystal sizes and generally shortens cirrus lifetime. Lower frequency waves modulate this evolution by setting the slowly varying background temperature. Cooling phases promote crystal growth and favor long-lived cirrus, while warming phases enhance rapid cloud decay. The simulated lifetime distribution reproduces the strongly skewed distribution of observed thin tropical cirrus lifetimes, including a non negligible population of clouds which persists longer than 12 h, and dominates the total cloud coverage.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
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.- Preprint
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RC1: 'Comment on egusphere-2026-3112', Anonymous Referee #4, 21 Sep 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-3112/egusphere-2026-3112-RC1-supplement.pdfCitation: https://doi.org/
10.5194/egusphere-2026-3112-RC1 -
RC2: 'Comment on egusphere-2026-3112', Anonymous Referee #5, 22 Sep 2026
Review of “On the Role of Atmospheric Waves in Governing the Persistence of Thin Cirrus Clouds in the Tropical Tropopause Layer” by Corcos et al. 2026 submitted to Atmospheric Chemistry and Physics (ACP).
Summary:
This study uses a microphysics–dynamics-coupled column model constrained by balloon borne observations to examine the combined effects of cirrus microphysical processes (depositional growth, sublimation, and sedimentation) and tropical multiscale waves (high-frequency gravity waves and low-frequency inertia–gravity waves) on the lifetime statistics of thin cirrus clouds in the tropical tropopause layer (TTL). Cooling fluctuations and the associated supersaturation during updrafts promote ice crystal growth, whereas warming fluctuations and subsaturation during downdrafts favor sublimation. Sedimentation and sublimation jointly regulate cirrus lifetime: larger ice crystals that survive sublimation sediment more rapidly, while smaller crystals sediment more slowly but are more susceptible to complete sublimation. Effects of high-frequency GWs are stochastic while effects of low-frequency waves are deterministic and phase-dependent. Long-lived TTL thin in situ cirrus therefore emerge from a delicate balance among these coupled microphysical and dynamical processes. The simulations identify a stabilization regime in which ice crystals grow large enough to resist to full sublimation but remain sufficiently small to avoid rapid sedimentation, eventually terminated by slow sedimentation. This study narrows knowledge gap by providing an explanation for the observed skewed distribution of TTL thin cirrus lifetime.
The study also acknowledges several caveats, including the vertically homogeneous ice-saturated column assumption, omission of ice nucleation, vertical wind shear, and turbulent mixing, and exclusion of other low-frequency waves.
Overall, the simulation results are insightful and robust. The conclusions are well supported by a clearly defined model setup and detailed exploration of the underlying mechanisms and factors. The manuscript is well written that presents a coherent and logical narrative.
Recommendation: accept in its current form.
Minor comments:
- Line 105: if so, I am curious how long is appropriate for robust statistical analysis?
- Is it possible that the GW parameterization includes other lower frequency waves?
Citation: https://doi.org/10.5194/egusphere-2026-3112-RC2 -
RC3: 'Comment on egusphere-2026-3112', Anonymous Referee #2, 01 Oct 2026
Review of
On the Role of Atmospheric Waves in Governing the Persistence of Thin Cirrus Clouds in the Tropical Tropopause Layer
by Corcos et al.
Summary and general comment
In this study the effect of gravity waves in combination with large scale waves on tropical tropopause cirrus clouds is investigated using a detailed microphysical model, which is driven by local dynamics. It is found that GWs can lead to a longer life time of very thin (e.g. subvisible) cirrus clouds.
This is a meaningful contribution to ACP. The overall findings are not really surprising, however somewhat expectable; the enhanced growth by fluctuating gravity waves and thus extension of life time is quite obvious from former studies of some of the authors. Nevertheless, the detailed investigation adds some new insights to our knowledge about ice clouds in the TTL.
Generally, this is a well written manuscript that constitutes a valuable contribution to ACP. However, I have some concerns on the (missing) description of the model and other issues. Therefore I recommend major revision for the manuscript, before it can be accepted. In the following I will explain my concerns in detail.
Major issues
(1) Missing description of the model
The model is not really explained in the manuscript, it is just referred to a former publication. Actually, it is not even stated in a meaningful or understandable way what kind of model is really used (in terms of bulk, bin, superdroplets etc.). I would guess that the authors use a superdroplet method, when they refer to the “simulation ice particles (SIP)”, but this is not explained well. The same applies for the description of the relevant processes. Only the growth/evaporation process is described in the appendix A; however, the procedure for the sedimentation of particles is not explained at all. I can understand that the authors do not want to repeat their model description in details; however, in the current state the model and the following results cannot be understood without given more information.
In addition, basic assumptions (as e.g. the shape of ice particles – probably spheres) are missing or are just provided in a sparse way. There is a long explanation about deriving the mean radius from LIDAR measurements, but on the other hand the authors do not mention any value for the typical number concentrations (although the pairs (n,m) are described in the same paragraph).
I suggest to rewrite section 2 in order to provide enough information about the general setting of the model. Details might be shifted into the appendix.
(2) Inconsistency in modeling ice physics and radiation
As far as I understand the model really describes the evolution of a size/mass distribution of ice particles, i.e. it is a very detailed model. On the other hand, the calculations of the radiative properties, a very simple radiation model (Corti and Peter, 2009) is used. This model is even simpler than a standard two-stream radiation code, which usually uses inputs of ice water content and effective radius. It is not clear why the authors do not make a larger effort to calculate the radiative effects directly from the model output, however instead use this very crude approximation based on optical depth. The comparison by Lotti et al. (2017) shows that there can be a large difference between the Corti and Peter model and a standard (not even sophisticated) radiation code – in contrast to the statement in the manuscript.
I would suggest to use at least a standard radiation model (e.g. Fu and Liou, 1993) for the calculation of the radiative properties.
(3) Representation of results
The description of the results is hard to understand, especially the figures. For instance, it is not really clear what is shown on the left panel of figure 4. It is not really helpful that two different labels are used for describing the processes AND the number concentration itself – by the way this is the only place where values of the number concentration are shown.
(4) Processes for small ice particles
Two of the authors (BK and EJ) have recently published an article about gravity waves and ice clouds in the tropical tropopause region (Jensen et al., 2024), claiming that the Kelvin effect might play a very important role for the sublimation of very small particles (smaller than 10 micro meter). Since in this model study the ice particles are of the same size, this effect might be important for the surviving of small ice particles. Is this effect included in the model? If not, why not, is there a good argument why to leave this effect out?
References:
Fu and Liou, 1993: Parameterization of the Radiative Properties of Cirrus Clouds. Journal of Atmospheric Sciences, 50, 13, 2008-2025.
Jensen, E. J., Kärcher, B., Woods, S., Krämer, M., & Ueyama, R. (2024). The impact of gravity waves on the evolution of tropical anvil cirrus microphysical properties. Journal of Geophysical Research: Atmospheres, 129, e2023JD039887. https://doi.org/10.1029/2023JD039887
Citation: https://doi.org/10.5194/egusphere-2026-3112-RC3
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