| 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.
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.