the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 11 Jun 2026
A Triple-Structured Mesospheric Climate Pattern Driven by a Double-Celled Meridional Circulation during the Equinox-Solstice Transition Months of November and May
Abstract. The upper mesosphere is a dynamically and chemically complex region where interannual climate variability remains incompletely understood, particularly during the transition months between the equinox and solstice circulation regimes. Using multi-satellite observations from MLS and SABER, we investigate the coupled dynamical-microphysical-chemical-thermal structures during November and May, building on the bottom-up mechanism of “upwelling—water vapor (H2O)—ozone (O3)—temperature”. We employ temperature near 80 km (the T80 index) as a proxy for upwelling intensity and identify two distinct centers: a summer polar upwelling and a tropical upwelling. Together they drive a double-celled anomalous meridional circulation that organizes the global climate into a novel triple-structured pattern, with coherent signatures in the summer high-latitude, equatorial, and winter high-latitude regions. A key finding is that hydration occurs below polar mesospheric clouds (PMCs) without pronounced dehydration above them. This “hydration-without-dehydration” configuration, made possible by the weak PMCs typical of November and May, indicates the dominance of the cold-trap effect over the conventional freeze-drying effect. The absence of dehydration further isolates the temperature-dependent ozone kinetic pathway for polar ozone enhancement, a pathway that is otherwise convolved with dehydration effects in stronger PMC seasons. Ozone and atomic oxygen (O) respond to the combined influences of meridional H2O transport and local thermal forcing, and the resulting radiative and chemical heating governs temperatures near 90 km (T90). These results establish the structure of the transitional climate regime, demonstrating that the shift from symmetric (equinox) to antisymmetric (solstice) variability is mediated by a well-organized, upwelling-driven double-celled circulation.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-2688', Anonymous Referee #1, 14 Jul 2026
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RC2: 'Comment on egusphere-2026-2688', Anonymous Referee #2, 16 Jul 2026
Review of Zhang and Liu:
Using satellite observations from MLS and SABER, this paper investigates the coupled dynamical-microphysical chemical-thermal structures during November and May. The paper specifically aims to address three questions: (1) What is the spatial pattern of interannual variability in H2O, H, O3, O, and temperature in the MLT during November and May? (2) What anomalous meridional circulation structure generates this pattern? (3) How do PMCs and ozone chemistry operate under these unique transitional conditions, and what do they reveal about the competing PMC microphysical framework? The main methodology is a correlation between the observed tracers and a “T80” index which is an index for mesospheric vertical motions. The correlation is done between an interannual time-series of these tracers and the index. Based on the correlations, the paper concludes that in November and May, there is a double-celled anomalous meridional circulation that organizes the global climate into a novel triple-structured pattern, with coherent signatures in the summer high-latitude, equatorial, and winter high-latitude regions.
I am rejecting this paper based on the following major issues:
The first major issue is that the science questions and methodology are very clearly focused on the interannual variability of the tracers in May and November and determining the circulation, but the results are being interpreted as though the questions and methodology were focused on seasonal climatology. In addition, the third science question is focused on PMC microphysics and variability, but the methodology and the results never answer this. But they do mention it extensively in the discussion section as though it was answered.
The second major issue is how the paper argues “control” or “causal mechanisms” but the methodology doesn’t allow this. The methodology is centered on correlation which isn’t causation. To establish causation, you need to calculate momentum budget, energy budget and mass budgets as well as chemical and transport time-scales over a much shorter period.
Other comments:
Line 43: What do you constantly mean by ‘anomalous circulation’? Why is it ‘anomalous’ when you are arguing that it is a climatology?
Line 125 (Entire section on “Multi-satellite data”): Both these datasets have limitations (e.g. sampling, retrieval algorithm, etc) that need to be detailed in this section. You should then address how your eventual results could be impacted by these limitations. Your methodology here makes it seem like you are working with first principles Physics-based model dataset. Also, you are interested in PMCs and microphysics but you clearly don't have data on that.
Line 157 (Entire section on “Bottom-up control mechanism framework”): It is not very clear as to what you mean by 'framework'. Is this an hypothesis you are testing? Also, the "chain" you are suggesting is an oversimplification of a wide-range of chemistry and dynamics behind O3, H2O, O and H.
Line 168 – 180: You need to ease your readers into your figures. You jumped into three very complicated figures too fast without even adequately describing them and clearly indicating their main points. Also, it isn't even clear as to what your main topic sentences are in these paragraphs.
Line 169: Where is this 'above PMCs'? As you mentioned and as is well known, PMC's aren't frequent in November. You don’t have data on this.
Line 169: Figure 2 is showing the relationship of your variables-of-interest in November across interannual time-scales. This is more appropriate for an analysis focused on interannual forcing for a specific month. This is not the same as showing the relationship of your variables-of-interest solely for a specific month. To do that, your correlation should have been on hourly data for an entire month.
Line 170: How do you detect dehydration? Positive correlation of T80 and H2O as in your previous paper? If so, how? A positive correlation suggests upwelling coincides with reduction in H2O but the causal relationship there is extremely unclear. I'd rather interpret that as H2O is being controlled by something other than vertical motion.
Line 173: SABER Hydrogen data isn't widely validated. You need to address that and make sure it is also considered in your results.
Line 181: Since your interest in November and May, I don't think the terms "summer" or "winter" are appropriate in this paper.
Line 189: O3 has a very fast chemical life-time. How would it be directly influenced by upwelling or any transport process? You don't have proof of that.
Line 189 – 190: Temperature in this region is (and as you also mentioned) strongly controlled by adiabatic processes. How would O3 suddenly be a major driver?
Line 205 – 208: This statement is purely speculative. You need more proof of this connection. Unlike the troposphere and stratosphere, the mesospheric circulations in the tropics tend to be a bit more independent from the poles. Tropical mesospheric circulations have its own semiannual oscillation.
Line 245: This is extremely vague. The winter hemisphere is governed by a lot of things. Also, since your analyzing November and May, I'm not sure "winter" is an appropriate term here.
Line 290 – 296: The presented interannual correlations between a vertical motion index and the tracers (and temperature) didn't adequately show this "double-celled anomalous meridional circulation". Based on your results, it is still not clear to me as to how this exactly looks. To the best that I can tell, it looks like, for interannual time-scales, there is semblance of tropical upwelling and polar upwelling (inducing adiabatic cooling) but that is it. But it can also be weak downwelling. All you showed was an index and its correlations with these tracers. Also, your figure 11 shows meridional motions, how did you get that?
Line 313: Again, how did you arrive at these meridional motions?
Line 354 (Entire section on “Microphysics of transitional PMCs: evidence for the cold-trap effect”). There are parts of this sub-section that can be included in a "discussion section". The problem is that the paper currently makes it seem like this is a major component and finding of the paper when it clearly isn't. You never even use any data to support this.
Line 470 – 473: You acknowledge that correlation isn't causation but your paper is currently written in a way that strongly argues causation. Acknowledging this doesn’t automatically clarify all your arguments in the paper. You will still need to substantially revise the entire paper.
Citation: https://doi.org/10.5194/egusphere-2026-2688-RC2
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- 1
Review comments on ACP manuscript egusphere-2026-2688 “A Triple-Structured Mesospheric Climate Pattern Driven by a Double-Celled Meridional Circulation during the Equinox-Solstice Transition Months of November and May” by Liang Zhang and Zhongfang Liu
This manuscript investigates the dynamical, chemical, and thermal structure of the upper mesosphere during the transition months of November and May using MLS and SABER satellite observations. The authors propose that a double-celled anomalous meridional circulation, diagnosed using a temperature-based upwelling proxy (T80), produces a triple-structured climate pattern through a bottom-up mechanism linking upwelling, H₂O, odd oxygen (Ox), and mesopause temperature (T90). The manuscript further argues that the absence of dehydration above weak polar mesospheric clouds (PMCs) during the transition months provides evidence for the cold-trap mechanism and allows the thermal contribution of ozone chemistry to be isolated from dehydration effects. Based on these analyses, the authors conclude that the transitional climate regime is primarily governed by a causal framework upwelling → H2O(H) → O3(O) → T90 rather than external forcings such as the solar cycle or CO₂-induced cooling.
I recommend rejection of this manuscript because I have fundamental concerns regarding the scientific framework and interpretation of the results.
While the topic is potentially interesting, the manuscript's central scientific framework is not convincingly supported by the analyses. The confusion between seasonal climatology and interannual variability, the incomplete treatment of the mesopause energy budget, and the repeated interpretation of correlations as evidence of causation together undermine confidence in the principal conclusions.
Specifically:
1. The scientific conclusions are not supported by the analyses.
The manuscript proposes a causal framework upwelling → H2O(H) → O3(O) → T90 and then uses statistical correlations to infer double-celled meridional circulation, ozone chemistry, the dominant physical mechanisms, and the energetics governing the transition months.
However, the analyses do not demonstrate these causal relationships. They are based almost entirely on correlations, while the dynamical, radiative, and chemical processes in the region is much more tightly coupled than the manuscript acknowledges. In particular, the role of radiative cooling, chemical heating, and atmospheric dynamics cannot be separated using the presented analyses alone. Consequently, many of the central conclusions are speculative and stronger than warranted by the evidence.
2. The manuscript confuses seasonal climatology with interannual variability.
The manuscript repeatedly states that it investigates interannual variability, yet its scientific questions concern the transition months of November and May and the circulation structure characteristic of those months. The conclusions are therefore about the seasonal (intra-annual) transition between equinox and solstice rather than interannual variability.
Moreover, the manuscript appears to use correlations among different Novembers (or different Mays) to infer the mechanisms governing the climatological November/May circulation. That logical connection is never established. As a result, the scientific objective and interpretation remain internally inconsistent.
3. The treatment of the mesopause energy budget is physically incomplete.
The manuscript attributes the observed temperature structure primarily to the proposed bottom-up chain involving H2O, ozone, and chemical heating, while giving insufficient consideration to the dominant radiative processes controlling mesopause temperatures.
In particular, CO2 infrared cooling is treated largely as a background climate forcing, whereas it is a fundamental component of the instantaneous mesopause energy budget. CO2 cooling depends on CO2 abundance, atomic oxygen, molecular nitrogen and oxygen, and temperature, and thus, is dynamically coupled with the very variables used to construct the proposed causal chain.
Without accounting for this coupling, the inferred circulation, ozone chemistry, and energetic pathways cannot be uniquely identified from the presented observations.
4. Correlation is repeatedly interpreted as evidence of physical causation.
Throughout the manuscript, statistical relationships are presented as confirming physical mechanisms. Words such as demonstrates, establishes, governs, and confirms are repeatedly used, although the evidence is based primarily on regression and correlation analyses.
Given the complexity of the coupled dynamical-radiative-chemical system in the region, stronger physical justification or numerical modeling would be required before drawing such causal conclusions.