-Response of the large-scale atmospheric circulation to climate change, including shifts and changes in intensity of the jet stream, Hadley and Walker cells, intertropical convergence zone, and monsoons;
-Changes in storm track intensity and structure in response to climate change and/or internal variability;
-Representation of the large-scale atmospheric circulation in climate models: inter-model variability, model biases, and methodologies for reducing uncertainty in model projections;
-Novel metrics and analysis methods for studying the large-scale atmospheric circulation;
-Interactions between the different components of the large-scale circulation, including tropical-extratropical interactions and teleconnection patterns;
-Role of moisture in the large-scale atmospheric circulation;
-Energy transport by the large-scale atmospheric circulation;
-Stratospheric-tropospheric interactions affecting the large-scale circulation.
The Walker circulation's rising branch is located over the warm water in the Western Pacific Warm Pool, and the air sinks over the cold Eastern Pacific. It is usually taken for granted that the Walker circulation exists because the dynamic ocean induces this SST gradient: efficient dynamical cooling by upwelling water keeps the SST cold in the East, while the warm water piles up in the West.
Here, we revisit this paradigm and offer a new perspective on the origin of the Walker circulation. We show that a Walker circulation arises even in climate model simulations with a zonally symmetric slab ocean where there is no oceanically forced zonal temperature gradient. Instead, a zonally asymmetric land distribution is sufficient to elicit a realistic Walker circulation. We find that the presence of South America alone can cause an atmospheric heating profile which forces a pan-tropical wave response leading to a Walker circulation. Rather than the oceanically induced SST gradient, we emphasize the importance of cold/dry advection from the subtropical anticyclones for explaining the climatological existence of the Walker circulation. Furthermore, we demonstrate the importance of water vapor and cloud feedbacks in amplifying the perturbation that creates the Walker circulation.
Our results show that the canonical coupled air-sea framework of the Walker circulation is incomplete, and that land-driven atmospheric teleconnections play a fundamental role in setting up the climatological Walker circulation.
How to cite: Günther, M. and Kang, S. M.: Revisiting the origin of the Walker circulation: the importance of land, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5907, https://doi.org/10.5194/egusphere-egu26-5907, 2026.
The Hadley circulation is the primary large-scale meridional circulation in the tropics and is conventionally seen as axisymmetric. However, meridional dynamics in the tropics are far from zonally uniform and recent developments have highlighted the importance of contributions from regional and time confined meridional overturning circulations to the global Hadley regime.
In the present work, we decompose the Hadley circulation into axisymmetric modes (AMs) which retain the linearized dynamics of an axisymmetric atmospheric circulation. Such modes are the normal mode solutions of the linearized axisymmetric equations of horizontal atmospheric motion, which coincide with the zonal wavenumber zero (k = 0) normal mode solutions to the linearized equations of horizontal atmospheric motion (Laplace tidal equations). We propose a method for the decomposition into AMs which draws similarities to previously developed local identification methods for equatorial waves ([1] and [2]).
The diagnostic potential of the decomposition is shown by analysing the preferred AMs of the Hadley circulation and recalling their physical underpinnings. In the literature, axisymmetric theory and constraints are frequently employed in the study of zonally confined meridional circulations ([3]). Therefore, we also analyse the validity and applicability of the decomposition into AMs in the case of zonally confined regional overturning circulations. Our work aims to be a contribution to the study of different regional meridional overturning regimes and the analysis of the regional contributions to the global Hadley circulation.
References:
[1] Cruz, J.B., Castanheira, J.M. & DaCamara, C.C. (2024) Local identification of equatorial Kelvin waves in real-time operational forecasts. Quarterly Journal of the Royal Meteorological Society, 150(761), 2440–2457. https://doi.org/10.1002/qj.4717
[2] Cruz, J.B., DaCamara, C.C. & Castanheira, J.M. (2025) Local identification of equatorial mixed Rossby–gravity waves. Quarterly Journal of the Royal Meteorological Society, 151(770), e4978. https://doi.org/10.1002/qj.4978
[3] Geen, R., Bordoni, S., Battisti, D. S., & Hui, K. (2020). Monsoons, ITCZs, and the concept of the global monsoon. Reviews of Geophysics, 58, e2020RG000700. https://doi.org/10.1029/2020RG000700
This work is supported by FCT, I.P./MCTES through national funds (PIDDAC): LA/P/0068/2020- https://doi.org/10.54499/LA/P/0068/2020 , UID/50019/2025, https://doi.org/10.54499/UID/PRR/50019/2025 , UID/PRR2/50019/2025, UID/50017/2025 (doi.org/10.54499/UID/50017/2025) and LA/P/0094/2020 (doi.org/10.54499/LA/P/0094/2020).
How to cite: B. Cruz, J., C. DaCamara, C., and M. Castanheira, J.: Dynamical Axisymmetric Modes of the Hadley Circulation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7887, https://doi.org/10.5194/egusphere-egu26-7887, 2026.
While a range of processes have been linked to uncertainty in tropical precipitation minus evaporation (P–E) and circulation changes, growing evidence links cloud-radiative changes to inter-model spread. Radiation-locking studies further demonstrate strong sensitivities of circulation and P–E to cloud-radiative changes in aquaplanet models; however, the physical mechanisms linking CO2-driven cloud-radiative changes to tropical circulation and P–E responses remain poorly understood. Here, we use the radiation-locking technique to elucidate these mechanisms in a climate model configured with realistic continents, sea ice, and a seasonal cycle, with the ocean represented by a slab ocean model with prescribed climatological q-fluxes. We introduce a novel analytical framework in which the P–E response is analysed as a function of climatological P–E, enabling direct comparison with thermodynamic scaling arguments.
Despite inducing weak surface warming, CO2-driven cloud-radiative changes substantially modify the tropical hydrological response, driving a robust wet-gets-drier, dry-gets-wetter P–E pattern that opposes the canonical wet-gets-wetter, dry-gets-drier signal associated with climate warming. Moisture and moist static energy budget analyses show that this response is driven by a weakening of the tropical overturning circulation associated with enhanced upper-tropospheric cloud-radiative heating. Sea surface temperature pattern changes induce additional P–E responses, including a poleward shift of precipitation maxima over the Indian and western Pacific Oceans. Our results demonstrate that circulation changes strongly shape tropical P–E responses to cloud-radiative changes, and that the balance between dynamic and thermodynamic responses may be a key control on inter-model spread. We further highlight the coupling between cloud-radiative heating and latent heat release as critical for the resulting circulation response.
How to cite: Van de Koot, E., Woollings, T., Byrne, M., and Voigt, A.: Dynamical controls on tropical circulation and precipitation–evaporation responses to cloud radiative changes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5883, https://doi.org/10.5194/egusphere-egu26-5883, 2026.
Radiative transfer lies at the heart of Earth's climate system, governing the fundamental energy balance that drives atmospheric circulation and the hydrological cycle. Yet idealized climate models often use gray radiation schemes, which ignore the spectral nature of light. These schemes are easy to use and simple to understand, but this simplicity comes at a cost: gray radiation fundamentally distorts the large-scale atmospheric circulation and its response to climate change.
Using an idealized aquaplanet GCM with a hierarchy of radiation schemes, I show that gray radiation produces a tropopause that is too low, a subtropical jet that is displaced equatorward, and a Hadley Cell that is too weak. Under warming, gray radiation underestimates tropical upper-tropospheric amplification and produces unrealistic changes in jet structure and Hadley Cell strength.
I then introduce the “Simple Spectral Model” (SSM), a radiation scheme which represents the spectral nature of greenhouse gas absorption using simple, analytic fits. This scheme is simple and easy to understand (like gray radiation), but faithfully represents the spectral nature of radiative transfer. I show that this scheme alleviates the significant circulation biases associated with gray radiation, and provides a more accurate picture of the response of the large-scale atmospheric circulation to warming. This work demonstrates that radiative transfer is not merely a "detail" in climate modeling, but that it fundamentally shapes the atmospheric circulation.
How to cite: Williams, A. I. L.: How radiative transfer assumptions shape the large-scale atmospheric circulation and its response to warming, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5953, https://doi.org/10.5194/egusphere-egu26-5953, 2026.
Equilibrium climate sensitivity remains highly uncertain due to cloud feedbacks, which are strongly influenced by the pattern effect—the dependence of the atmospheric response and radiative feedbacks on the spatially heterogeneous sea surface warming. The pattern effect depends on the representation of convection, boundary-layer dynamics, and the large-scale circulation. Because it links small-scale processes with global climate, it provides an ideal test of the added value of global storm resolving models for simulating climate dynamics.
We investigate the atmospheric response to an idealized 1.5 °C sea surface temperature perturbation applied to the Indo-Pacific Warm Pool using the ICON model in the XPP configuration across a range of horizontal resolutions, from CMIP-like scales to kilometer-scale simulations. A set of experiments spanning different physical parameter configurations is used to examine how variations in moisture and convective processes influence the large-scale circulation response to regional warming. While higher resolution tends to produce a stronger response, differences in moisture distribution associated with changes in the ITCZ and Walker circulation, as well as variations in convective aggregation, exert a comparably strong influence on the circulation adjustment.
These results demonstrate that the coupling between moisture, convection, gravity-wave processes, and the large-scale circulation is a key control on the simulated pattern effect, shaping the atmospheric response to spatially heterogeneous warming and influencing circulation-driven climate feedbacks under climate change.
How to cite: Kroll, C. and Jnglin Wills, R. C.: The pattern effect in storm resolving ICON: How newly resolved processes influence the moisture distribution and large-scale circulation response to sea surface temperature perturbations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3160, https://doi.org/10.5194/egusphere-egu26-3160, 2026.
Extratropical forcing can generate strong non-local responses via teleconnections. For example, the Hadley circulation responds to high-latitude forcing by shifting its ascending branch, the intertropical convergence zone (ITCZ), towards the warmer hemisphere. However, the ITCZ location has been shown to modulate the inter-hemispheric communication of an extratropical surface anomaly through the ITCZ blocking mechanism.
In this study, we investigate how the climatological ITCZ position affects the climate response to extratropical forcing. We conduct aquaplanet slab ocean simulations in MPI-ESM by imposing a southern hemispheric extratropical cooling of 50 Wm-2 to five control states, each differing in the ITCZ location.
Results show that the Hadley cell response and consequent ITCZ northward shift are the largest when the climatological ITCZ is in the same hemisphere as the forcing. Both responses progressively weaken as the climatological ITCZ is displaced northward.
The amplitude and progressive weakening of the atmospheric response are shaped by the cloud radiative effect (CRE). If the ITCZ lies in the forced hemisphere, extratropical low-cloud formation enhances the imposed cooling locally, thus increasing the atmospheric compensation for the energetic imbalance. However, when the ITCZ is in the opposite hemisphere, a weak but positive low-cloud anomaly extending equatorward from the forced extratropics results in a dampened atmospheric compensation.
Locking the clouds mutes the atmospheric response, further highlighting the role of cloud feedbacks for ITCZ shifts.
Furthermore, we show that the negative sea surface temperature (SST) anomaly originating in the forced extratropics does not extend substancially beyond the ITCZ, reinforcing the idea that the ITCZ location limits the propagation of surface signals. We propose that changes in latent heat fluxes tied to the surface-wind response to the forcing are at the core of the ITCZ blocking mechanism, as an anomalous increase (decrease) in wind speed southward (northward) of the new ITCZ location leads to an enhancement (reduction) of the negative SST anomaly.
Our findings reveal that the ITCZ location and blocking effect strongly modulate extratropical-tropical interactions, implying that model biases in the ITCZ location might produce inaccurate responses to high-latitude forcing.
How to cite: Collavini, V., Günther, M., and Kang, S. M.: Dependence of inter-hemispheric teleconnections on the climatological ITCZ pattern, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5844, https://doi.org/10.5194/egusphere-egu26-5844, 2026.
Hierarchical modelling is a valuable tool, which has supported our understanding of, for example, controls on jet latitude, and the nature of monsoon circulations. However, it is not always clear if and how the insights developed in simpler models, such as aquaplanets, generalise to more realistic situations (e.g. CMIP or reanalysis). Here, we present a new, interpretable machine learning framework for translating dynamical insights across the model hierarchy, and show how this can develop our understanding of large-scale monsoon circulations.
Our goal is to identify dominant balances between terms in the governing equations, which characterise dynamical regimes. We identify these balances, both regionally and across the climatological year, at each stage in a model hierarchy. Our hierarchy comprises simulations with different levels of complexity in the lower boundary conditions, from aquaplanets up to reanalysis. This approach allows us to explore when, where, how and why different dynamical processes arise at each level in the model hierarchy, and to investigate how their extents and timings are altered by changes to model parameters.
Specifically, we employ NEMI, a pipeline previously applied to the vorticity budget of realistic ocean simulations. This pipeline uses UMAP to reduce the complexity of the selected equation into a low-dimensional latent space. Agglomerative hierarchical clustering, along with a combinatorial hypothesis selection algorithm, then facilitate partitioning and labelling the latent space into distinct dynamical regimes. Evaluating entropy, a measure of how consistently a sample is assigned to a given cluster, allows us to objectively choose appropriate hyperparameters, and also conveniently allows study of the regional and seasonal robustness of the different regimes identified.
We apply NEMI to the 200-hPa momentum budget, which has previously been used to study the Hadley cells in aquaplanets. We demonstrate how parallels to known regimes identified in aquaplanets can then be objectively studied in more complex datasets such as ERA5. Within the global tropics, in addition to angular momentum conserving/eddy-driven Hadley circulations, we identify regimes influenced by geostrophic balance and rotational flows. Implications for our understanding of the tropical circulation are discussed.
How to cite: Dutta, A., Geen, R., and Sonnewald, M.: Unlocking Dynamical Insights across the Model Hierarchy with Interpretable Machine Learning, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19069, https://doi.org/10.5194/egusphere-egu26-19069, 2026.
The Western Pacific Hadley Circulation (WPHC), the strongest regional Hadley circulation, plays a crucial role in regional and global climate variability. Observations since 1979 indicate a significant strengthening of the boreal spring WPHC in the Northern Hemisphere; however, the relative roles of internal climate variability and external forcing remain unclear. Here, using large ensemble climate simulations together with observational constraints, we quantify the drivers of recent WPHC changes and provide near-term future projections.
We show that approximately 71% of the observed strengthening is attributable to internal variability associated with phase transitions in three key tropical inter-basin sea surface temperature (SST) gradients—tropical Western Pacific (TWP)-Western North Pacific, TWP-Tropical Eastern Pacific, and TWP-Tropical Indian Ocean. By constraining future projections using ensemble members that better reproduce the historical evolution of these SST gradients, we reduce projection uncertainty by nearly 49%. The constrained projections consistently indicate a likely weakening of the WPHC in the coming decades.
Our results highlight the critical importance of tropical inter-basin SST gradients in shaping regional Hadley circulation variability and underscore their value for improving the reliability of near-term regional climate projections.
How to cite: Xu, W., Chen, W., and Chen, S.: Recent strengthening of the Western Pacific Hadley Circulation driven by tropical inter-basin sea surface temperature gradients, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1784, https://doi.org/10.5194/egusphere-egu26-1784, 2026.
Midlatitude storms transport warm and moist air poleward and upward, releasing latent heat. Latent heating is thus organized by the
circulation but then modifies temperature gradients and winds, constituting a nonlinear feedback. We define the latent heating feedback
as the effects that arise from latent heating being coupled with the circulation. Because of its nonlinearity, the climatic effects of this
feedback are difficult to isolate and remain poorly understood.
By decoupling latent heating from the circulation in an atmospheric general circulation model, we show that the latent heating feedback
enhances storm track eddy diffusivity, modifying eddy heat fluxes beyond changes in mean baroclinicity. Simultaneously, tracked storms
occur at lower latitudes, intensify more, and propagate further poleward, while the subtropical jet strengthens as coupled latent heating
preserves lower latitude baroclinicity. The feedback response supports the idea that diabatic effects cause the “too zonal, too
equatorward” storm track biases in climate models.
Finally, we extend the analysis to climate change experiments where we isolate the contribution from the latent heating feedback on
storm intensity and eddy kinetic energy as the world warms. The feedback is most important in summer where it accounts for most of the
changes in eddy kinetic energy. In winter, the feedback is constrained. Isolating the latent heating
feedback helps to quantify how storminess changes as the atmosphere warms, which climate models currently struggle with.
How to cite: Auestad, H., Shibu, A., Ceppi, P., and Woollings, T.: The latent heating feedback on the midlatitude circulation in a warming world, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6613, https://doi.org/10.5194/egusphere-egu26-6613, 2026.
The North Atlantic eddy-driven jet strongly shapes Euro-Atlantic weather and climate. Its variability at subseasonal tiemescales is linked with regional storm tracks, atmospheric blocking, European weather and the occurrence of extreme events. However, how this variability responds to climate change has not yet been explored. Here, we use a novel jet diagnostic method to show that over the past 75 years, wintertime subseasonal variability in jet latitude and tilt has declined by 18% and 14%, respectively. Climate models indicate part of the reduction in jet variability is due to external forcing, although they tend to underestimate its magnitude. Models further project a continuous decline in jet variability throughout the 21st century under global warming. These findings reveal a robust response of the North Atlantic large-scale atmospheric circulation to climate change, and contribute to the growing body of evidence of a too low signal-to-noise in current climate models, with implications for current and future European weather predictability.
How to cite: Vacca, A. V., Perez, J., Bellomo, K., von Hardenberg, J., and Maycock, A.: Reduced subseasonal variability of the North Atlantic jet stream due to climate change, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11941, https://doi.org/10.5194/egusphere-egu26-11941, 2026.
The Pacific and Atlantic storm tracks are regions of enhanced storm activity that shape the Northern Hemisphere climate. According to the basic theory, stronger jet-streams should be associated with more intense storm activity. However, despite the Pacific jet being stronger in winter, storms over the Atlantic are more intense, a puzzling observation that has long challenged our understanding of midlatitude climate. Here, we address this paradox by analyzing how differences in jet orientation influence its interaction with midlatitude storms (cyclones). Using 84 years of ERA-5 data and tracks of all winter storms over this period (and JRA-3Q for validation), we show that the Pacific jet's zonally elongated structure forces storms to exit high jet intensity regions rapidly. Conversely, the Atlantic jet's tilted orientation aligns with the storms' trajectories, enabling storms to remain in high-intensity jet regions for extended periods. Lagrangian-Energetic analyses reveal that while Pacific storms exhibit rapid initial growth, over the Atlantic, prolonged exposure to strong jets drives greater energy extraction, resulting in storms that reach higher peak intensities and sustain their strength for longer durations. These findings reconcile the observed Northern Hemisphere winter storm track activity with basic theory, suggesting a new explanation for this long-standing question and underscoring the importance of capturing individual storm dynamics within the climate system to advance our understanding of present-day and future climates.
How to cite: Hadas, O. and Kaspi, Y.: Impact of Jet Stream Orientation on Northern Hemisphere Winter Storm Activity, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16925, https://doi.org/10.5194/egusphere-egu26-16925, 2026.
Subtropical land regions are projected to experience drying under increasing greenhouse gas concentrations due to widening of the tropical circulation. The magnitude and mechanisms of this response vary strongly across different regions. Using an idealised set-up for an atmospheric general circulation model coupled to a slab ocean, we investigate how the latitudinal position of a simplified square subtropical continental land mass influences the formation, extent and CO2 sensitivity of continental dry zones (CDZ). For all land positions, a continental dry zone emerges on the equatorward side of the land mass in boreal summer, extending significantly further poleward than the zonally symmetric edge of the Hadley cell. The poleward extent of the emerging CDZ is consistently constrained to a narrow latitude band in which subtropical subsidence weakens and midlatitude eddy activity increases. The amount of CDZ widening under CO2 increase strongly depends on the type of climatic dry zone established over land. Land configurations that produce persistent all-year round arid, continental-type dry climates exhibit weak sensitivity to circulation changes, while Mediterranean-type dry climates show enhanced dynamical drying associated with poleward CDZ expansion. These results provide a unifying framework for understanding why robust subtropical land drying in observations and projections is confined to very specific regions. The importance of differentiating continental dry zones by their climate regime is highlighted, underlining the heightened sensitivity of Mediterranean-type dry climates to circulation-driven drying under climate change.
How to cite: Doerfler, N. and Levermann, A.: Square Island on Aqua Planet: mechanisms of expansion of subtropical continental dry zones under CO2 increase, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12676, https://doi.org/10.5194/egusphere-egu26-12676, 2026.
The storm tracks along the two main western boundary currents, the Kuroshio-Oyashio and Gulf Stream, are an integral feature of the Northern Hemisphere climate. Even though diabatic processes play a fundamental role in the evolution of storm tracks, especially related to the enhanced water cycle along sea surface temperature fronts, our theoretical understanding of the impact of moist dynamic processes is still incomplete. To shed light on the relative importance of diabatic effects on storm tracks, we quantify diabatic and adiabatic contributions to variations in baroclinicity using a framework based on isentropic slope tendencies.
We reveal a dichotomy in the maintenance of baroclinicity between the near-surface and free troposphere. Specifically, changes in baroclinicity due to adiabatic and diabatic processes have opposite phases with adiabatic depletion preceding diabatic generation of baroclinicity in the near-surface, while diabatic generation precedes adiabatic depletion in the free troposphere.
In the near-surface troposphere, cold air outbreaks (CAOs) are the primary contributors to variability in baroclinicity, while outside of CAOs variability is significantly weaker and largely incoherent with the overall near-surface variability. In the free troposphere, on the other hand, most of the variability in baroclinicity is attributable to extra-tropical cyclones and fronts. Despite their limited areal extent, they explain more than half the total variance in baroclinicity. The contribution to total variability from atmospheric rivers is small, indicating that the presence of moisture alone does not necessarily translate into diabatic production of baroclinicity in the absence of a mechanism for ascent.
How to cite: Marcheggiani, A., Dacre, H., Spensberger, C., and Spengler, T.: Diabatic processes on synoptic timescales drive variability in midlatitude storm tracks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12553, https://doi.org/10.5194/egusphere-egu26-12553, 2026.
The maintenance of the storm tracks relies on maintaining the baroclinic zones from which mid-latitude cyclones develop. By expressing baroclinicity (a standard measure of baroclinic growth) in terms of dry entropy and constructing an entropy budget for the North Atlantic storm track, we find that the climatological maintenance of the storm track is due to large-scale advective processes in the free troposphere. We find the most important factor contributing to the maintenance of the baroclinic zone to be the import of cold continental air from North America towards the storm track, characterised by the zonal advection of lower entropy air masses. For eddy timescales, however, these advective processes weaken baroclinicity as they are dominated by the growth of weather systems. Our findings suggest that local diabatic effects, dominated by latent heating, are of secondary importance and may even damp the strength of the baroclinicity on average.
Our results indicate that the storm track in the N. Atlantic is essentially governed by the “discharging condenser” mechanism proposed by Jerome Namias in 1950. In that picture, the diabatic effects ultimately responsible for the maintenance of the N. Atlantic storm track are remote rather than local.
Namias, J. 1950. The index cycle and its role in the general circulation, Journal of Atmospheric Sciences 7, no. 2,
130 –139.
How to cite: Biddiscombe, R.: Maintaining the North Atlantic storm track, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6846, https://doi.org/10.5194/egusphere-egu26-6846, 2026.
When decomposing the atmospheric flow into a basic state and perturbations, the perturbations are generally interpreted as the contribution from chaotic non-linear weather. We explore the link between day-to-day weather and the climatological zonal mean perspective on zonal momentum in more detail by systematically linking eddy momentum fluxes to weather events. Specifically, we first decompose the full momentum flux divergence into contributions from mean flow and perturbations both in the time and zonal direction as well as their combinations, and then systematically relate synoptic jets, cyclones, and Rossby wave breaking events to the instantaneous momentum fluxes. We thus construct a step-by-step link between the time-zonal mean perspective on momentum flux convergence and the synoptic perspective.
With this approach, we show that both the time and zonal averaging are a residual of a large compensation of momentum flux convergence and divergence. In both dimensions, the mean must be regarded as a residual that is at least an order of magnitude smaller than the original signal. Further, a large fraction of eddy momentum flux convergence and divergence occurs in association with weather features, with synoptic jets alone accounting for 60-80% of the convergence from the subtropics throughout the mid-latitudes. Rossby wave breaking, on the other hand, only features less than 30% of the momentum flux convergence in the midlatitudes.
Finally, the attribution of the full-field momentum flux convergence is nearly indistinguishable from the attribution of eddy-momentum flux convergence, irrespective of whether the eddies are defined as perturbations in time, zonal direction, or the combination of both. The effect of stationary waves to the momentum fluxes is thus implicitly included in the selected transient weather events.
How to cite: Spengler, T., Spensberger, C., Konstali, K., Auestad, H., Marcheggiani, A., and Lachmy, O.: A weather feature perspective on jet dynamics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17438, https://doi.org/10.5194/egusphere-egu26-17438, 2026.
Some time ago, resonant amplification of Rossby waves along a circumglobal jetstream was hypothesized as the underlying reason for extreme weather in observed episodes. The argument is based on refractive index theory in the framework of the linear barotropic model. This theory allows one to diagnose the existence of a zonal waveguide - and, hence, the possibility of Rossby wave resonance - by a straightforward analysis of the meridional profile of the basic state zonal wind. The current paper contrasts the results from this theory with a recently developed method that makes less assumptions and approximations and is, hence, considered as benchmark. Comparison between the two methods shows that refractive index theory gives results that are both qualitatively and quantitatively inconsistent with the benchmark method. Experiments with idealized jets allow one to understand the shortcomings of refractive index theory. It is concluded that refractive index theory is fundamentally inappropriate as a diagnostic for Rossby wave resonance.
How to cite: Wirth, V.: How to diagnose Rossby wave resonance along a circumglobal jetstream?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2693, https://doi.org/10.5194/egusphere-egu26-2693, 2026.
Climate change is projected to have wide ranging impacts on atmospheric extreme events. However, it remains uncertain how a warming climate will influence the waviness of the jet stream and extreme wave-activity events in the midlatitude storm track. An objective identification of this phenomena is important as wave activity aloft plays an important role in driving the weather extremes over the continents. Here we use the local wave activity (LWA) metric to quantify stationary and transient wave activity during wintertime from multi-member ensembles of state-of-the-art climate model simulations including, NorESM, CESM-LENS2 and MPI-LE simulations for Historical and various SSP warming scenarios. Our analysis reveals a statistically significant decrease in the waviness of the jet stream and regional changes in the probability of extreme wave-activity events in the midlatitudes. These changes are found to be dynamically consistent with the theoretical predictions from the non-acceleration relation and the recently proposed traffic-jam theory of atmospheric blocking.
How to cite: Barpanda, P. and Li, C.: The dynamics of extreme wave-activity events in a warming climate., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21108, https://doi.org/10.5194/egusphere-egu26-21108, 2026.
Extreme heat events and severe convective storms are among the leading causes of weather-related damages in North America (NA). Under climate change, western NA highlands experience a faster rise in extreme near-surface temperatures, while central and eastern NA show stronger amplification of moist heat and convective activity. In recent theoretical work, we showed that low-level energy inversions significantly contribute to the buildup of near-surface moist heat and convection in the midlatitudes. Here, we demonstrate using CMIP6 simulations that future intensification of extreme moist heat over central NA is associated with substantial warming upstream over high terrains, which is advected eastward by strong westerlies, enhancing downstream low-level energy inversions. The projected increase in inversion strength provides a tight upper bound for the projected increase in near-surface moist heat. We further validate these findings through a General Circulation Model (GCM) experiment in which eliminating elevated heating over western high terrains substantially reduces extreme moist heat and convective instability across eastern NA. Our findings identify elevated heating and low-level inversions as critical drivers of compound heat-convection risks, offering new insights into the mechanisms and projected changes of midlatitude extreme weather.
How to cite: Tamarin Brodsky, T. and Li, F.: Enhanced Highland Warming Intensifies Midlatitude Moist Heat and Convection, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14250, https://doi.org/10.5194/egusphere-egu26-14250, 2026.
Recurrent and persistent large-scale circulation patterns, known as weather regimes, are widely employed in operational medium-range and subseasonal prediction. However, they have been used less often in studies of long-term climate variability and change. Here, we use a recently defined year-round North American regime classification to identify trends in the summertime circulation from 1981 to 2024. We find large increases in the frequency, persistence and interannual variability of the Greenland High (GH) regime, which is similar to Greenland blocking and the negative summer North Atlantic Oscillation. Recent extremes include the summers of 2023, 2019 and 2016. A first-order Markov model shows that the increased GH frequency and interannual variability can arise from increased GH persistence.
The GH frequency trend resembles previously reported trends in summertime Greenland blocking, which are absent in uninitialised climate models but have been seldom analysed in initialised models. We therefore investigate whether the observed GH trends can be reproduced by SEAS5, ECMWF’s current operational seasonal prediction system. To do so, we construct a 10,000-member ensemble by randomly sampling a single member from the May initialisation each year from 1981 to 2024 and stitching them together to create 10,000 different time series.
Our results show that the very large SEAS5 ensemble fails to capture the observed trend in GH frequency because persistence trends are too weak. This occurs despite SEAS5 producing summers with more GH days and individual regimes more persistent than observed, so the issue is not simply an overall inability of the model to generate persistent regimes. Hence, the missing GH trends must arise from fundamental model deficiencies which develop on subseasonal timescales and are not rectified by initialisation. Our work adds to a growing body of literature showing the benefit of using seasonal model data to understand the development of climate model trend errors.
How to cite: Lee, S. H. and Polvani, L. M.: Recent summertime North American weather regime trends in a very large seasonal model ensemble, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6707, https://doi.org/10.5194/egusphere-egu26-6707, 2026.
The western Pacific (WP) pattern, North Pacific Oscillation (NPO), and the Pacific-North American (PNA) pattern are dominant teleconnection patterns over the wintertime North Pacific, which are characterized by a meridional dipole of height anomalies. To comprehensively understand why these patterns are dominant, our previous study systematically extracted 286 meridional teleconnection patterns anchored at various locations spanning the basin from monthly mean fields and investigated the energetics for each of the patterns. The study quantitatively revealed that patterns that efficiently gain kinetic energy (KE) and available potential energy (APE) through the energy conversion from the climatological mean state and high-frequency eddies tend to have larger total energy (KE+APE), which explains the dominance of the specific teleconnection patterns. In addition, we found baroclinic energy conversion from the climatological mean field is the most efficient process for the maintenance of almost all the patterns, arising from the vertically phase-tilted height anomalies embedded in the baroclinic climatological mean state.
This result implies that the dominance of a pattern could change under different background states. The present study further investigated changes in energetics of the systematically extracted 286 teleconnection patterns under global warming through a comparison between d4PDF historical and +4K experiments. We found an increase in the total energy associated with patterns whose node lines are located at 35°N, including the PNA pattern, in the warmer climate, while an energy decrease is found for the patterns with node lines at 45°N, including the WP pattern and NPO. These energy changes are highly correlated with the changes in the net energy conversion efficiency. Changes in barotropic and baroclinic energy conversion efficiencies from the climatological mean state are the primary cause of the net efficiency changes, and those can be explained partly by structural changes in the background Pacific jet and decreased horizontal temperature gradients associated with Arctic amplification and more enhanced warming over land than over the ocean. Moreover, baroclinic conversion efficiency decreases for almost all the patterns due to the changes in the vertical structure of circulation anomalies and the background temperature field. These results provide clues for the mechanisms of the magnitude changes in the meridional teleconnection patterns and implications for the potential predictability in the warmer climate.
How to cite: Satoh, R. and Kosaka, Y.: Changes in Wintertime North Pacific Meridional Teleconnection Patterns due to Global Warming: An Energetics Perspective, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17106, https://doi.org/10.5194/egusphere-egu26-17106, 2026.
Ocean mesoscale sea surface temperature (SST) variability associated with eddies, fronts, and filaments strongly modulates air–sea heat and moisture exchanges, yet its role in shaping future regional climate change remains poorly constrained. This uncertainty largely stems from the fact that most global climate models do not resolve the ocean mesoscale. Here, we assess how the SST mesoscale influences the North Atlantic–European climate under present-day and future warming conditions. We use a high-resolution (~16 km) global atmospheric model forced with SSTs from an eddy-rich coupled model, comparing simulations with fully resolved mesoscale SSTs to experiments in which these have been spatially smoothed. While the atmospheric mean state shows only minor sensitivity to mesoscale SSTs under present-day conditions, under future climate conditions, mesoscale SST anomalies contribute to amplifying European winter climate change. Enhanced latent heat release along the Gulf Stream associated with mesoscale SST anomalies increases baroclinic instability, intensifies the North Atlantic storm track, and drives a circulation response resembling a positive phase of the North Atlantic Oscillation. This results in substantially warmer and wetter European winters. In contrast, suppressing mesoscale SST variability weakens storm activity, favors atmospheric blockings, and strongly reduces projected warming. Our results demonstrate that the ocean mesoscale exerts a first-order control on the response of the mid-latitude atmospheric circulation to climate warming, and suggest that climate projections based on standard resolution models may systematically underestimate regional climate change over Europe. Resolving mesoscale ocean–atmosphere interactions emerges as a key requirement for more reliable future climate projections.
How to cite: Ortega, P. and Moreno-Chamarro, E.: Amplified European future warming under mesoscale-resolving sea surface temperature forcing, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3310, https://doi.org/10.5194/egusphere-egu26-3310, 2026.
Double Jets (DJ) refer to a specific configuration of the large-scale atmospheric circulation in which the Northern Hemisphere polar and subtropical jets occur as two clearly separated branches. European heatwave trends have been linked to an increased persistence of Eurasian DJs (Rousi et al. Nat. Comms. 2022). However, it remains unclear to what extent observed trends are anthropogenically forced or associated with internal variability. A central necessity to answer this question is the ability of climate models to reproduce central DJ properties and their association with surface anomalies.
Based on models from the sixth phase of the Coupled Model Intercomparison Project (CMIP6), we provide first insights into model representation of DJ characteristics. Our findings show that most models qualitatively capture the structural configuration of the DJs, while systematically underestimating the magnitude of the polar jet branch by approximately 35%.We further demonstrate that this response is associated with an underestimation of the high-latitude (60°N–90°N) meridional temperature gradient across models, where models with weaker gradients exhibit weaker winds, in line with the thermal wind relation. Crucially, this underestimated polar jet intensity acts as a dynamical constraint, causing models to underestimate the cumulative heatwave intensity over Western Europe by approximately 30%.
Finally, by extending our analysis to future projections (2021–2100) under the SSP3-7.0 scenario we reveal a transition toward a weakened DJ regime. Our work highlights the need for improved representation of DJ characteristics and their coupling with heat extremes in climate models to enhance our confidence in future heat risk projections.
How to cite: Liu, S., Tian, Y., and Kornhuber, K.: Double Jet circulation regimes and their association with Western European Heatwaves in present and future climates, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13168, https://doi.org/10.5194/egusphere-egu26-13168, 2026.
Changing weather is an aspect of global warming potentially constituting a major challenge for humanity in the coming decades. Some climate models indicate that, due to global warming, future weather will become more persistent, as regard surface-air temperature anomalies lasting longer. However, to date, an observed change in weather persistence has not been robustly confirmed. Here we show that weather persistence in terms of temperature anomalies, across all weather types and seasons, has increased during recent decades in the Northern Hemisphere mid-latitudes.
This persistence increase is linked to Arctic temperature amplification – the Arctic warming faster than the global average – and hence global warming. The Arctic amplification weakens the meridional geopotential-height gradient at 500 hPa, which, through geostrophic balance and the thermal wind relation, leads to a reduction of the westerly zonal mass flow (density-weighted zonal winds integrated through the atmosphere) in the northern midlatitudes. The westerly atmospheric mass flow helps transport weather systems such as cyclones and other weather anomalies. Hence, when the background flow reduces, the transport of weather systems slows, and the local weather tends to become more persistent.
Persistent weather may lead to extreme weather, and for many plants such as crops, weather persistence can be devastating, as these plants often depend on weather variations. Hence, our results call for further investigation of weather-persistence impact on extreme weather, biodiversity, and the global food supply.
Graversen, R.G., White, R.H. & Vihma, T. Enhanced weather persistence due to amplified Arctic warming. Commun Earth Environ 6, 997 (2025). https://doi.org/10.1038/s43247-025-03050-1
How to cite: Graversen, R. G., White, R., and Vihma, T.: Enhanced weather persistence due to amplified Arctic warming, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7405, https://doi.org/10.5194/egusphere-egu26-7405, 2026.
Extratropical cyclones (ETCs) are the primary drivers of severe weather over the North Atlantic, yet projections of changes in the intensity of the most
extreme storms under climate change remain highly uncertain. This study investigates inter-model uncertainty in future climate projections of extreme cyclones in winter, arising from competing processes of reduced midlatitude baroclinicity and enhanced moisture availability. We assess their contributions to projected changes in extreme cyclone intensity.
We analyze the future changes in the most intense 100 ETCs in winter across 13 CMIP6 models under the highest forcing scenario (SSP5-8.5; 2070–2100 vs 1980–2010), using 850 hPa vorticity tracking and cyclone-centered composites of precipitation, near-surface temperature gradients, and surface winds. Our results show that the majority of models project an intensification of the most intense cyclones in the North Atlantic, relative to the historical runs, with an increase in precipitation associated with extratropical cyclones in 11 out of 13 models. Near-surface meridional temperature gradients, however, exhibits a weakening in 9 out of 13 models, reflecting reduced low-level baroclinicity.
Furthermore, surface wind projections reveal no clear consensus, with half of the models projecting strengthening and half projecting weakening of surface winds. In addition, 7 out of 13 models project an eastward shift in peak intensity towards northwestern Europe, while latitudinal changes lack a robust pattern.
Our results show that projected intensification of extreme North Atlantic cyclones in terms of vorticity is accompanied by robust thermodynamic sig-
nals, with intensified precipitation in most models despite weakened near-surface meridional temperature gradient. In contrast, the associated surface wind response shows large inter-model variability, with no consistent change across models, highlighting the need for further assessment of surface wind projections.
How to cite: Mercier, L. C., Afargan Gerstman, H., Priestley, M. D. K., Christensen, J. H., and Domeisen, D. I. V.: Quantifying the Inter-Model Uncertainty of Extreme Extratropical Cyclones in the North Atlantic winter in a Warming Climate , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7436, https://doi.org/10.5194/egusphere-egu26-7436, 2026.
The spatial footprint of extreme rainfall events (EREs) governs the extent of affected regions and strongly influences flood severity and socio-economic impacts. While changes in the intensity of precipitation extremes are relatively well understood, a robust physical framework for characterising their spatial scales remains lacking. In particular, it is unclear to what extent large-scale dynamical constraints regulate the size of extreme precipitation systems if they. In this study, we investigate whether the theoretical eddy length scale, specifically the Rhines scale and the Rossby radius of deformation, can provide a physical basis for understanding the spatial extent of EREs during ENSO. We examine whether variations in these length scales are reflected in observed changes in ERE size during El Niño–Southern Oscillation (ENSO), which is known to modulate the large-scale background flows. By stratifying EREs according to ENSO phase, we assess how changes in the background circulation during ENSO influence the relationship between eddy length scales and the spatial footprint of extreme rainfall. This work would provide a dynamical framework linking large-scale atmospheric eddy scales to precipitation extreme size. Results to be presented at the conference will discuss on the extent to which theoretical length scales constrain ERE spatial organisation and how these constraints vary across ENSO phases, with implications for understanding and projecting flood risk under climate variability.
How to cite: Devgan, A. and Nikumbh, A.: Does ENSO set the footprint of extreme rainfall? Insights from dynamical eddy length scales, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15986, https://doi.org/10.5194/egusphere-egu26-15986, 2026.
Predicting the spatial distribution, intensity, and variability of tropical precipitation is important in the context of present and future climate change. However, climate models have consistently failed to simulate tropical precipitation correctly, even as their resolution has progressively improved (Tian and Dong, 2020). Convective Available Potential Energy (CAPE) is a measure of the amount of buoyant energy usable by convection. Inspired by convective quasi-equilibrium theory (Arakawa, 1974), we test whether the rate of CAPE generation is a good indicator of tropical precipitation in the past four decades of the Japanese Reanalysis for Three Quarters of a Century. We find that CAPE generation predicts the spatial distribution and intensity of observed tropical precipitation significantly better than CAPE itself, as well as precipitation trends and extreme seasonal precipitation. CAPE generation is therefore a good proxy to study convective events which are too small to be directly simulated at the resolution of climate models. Further, we decompose the physical sources of buoyancy generation and find that local evaporation is the main energy source in the tropical rainbands, and surprisingly, heat and moisture convergence play a minor role in providing buoyancy for convection. Based on these conclusions, it may be more useful to study air-sea fluxes and local evaporation as a key to improving climate precipitation simulations.
How to cite: Figueroa, M., Fajber, R., and Huang, Y.: Monthly CAPE generation rates predict tropical precipitation., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13927, https://doi.org/10.5194/egusphere-egu26-13927, 2026.
The tropical atmosphere plays an important role in transporting energy poleward and driving the global circulation. However, understanding and simulating this fundamental aspect of our climate remains difficult due to its sensitivity to convective parameterizations and horizontal resolution. This study focuses on benchmarking the resolution dependence of tropical poleward energy transport in two aquaplanet atmospheric general circulation models with disabled convective parameterizations: a nonhydrostatic high-resolution (100–6 km) finite-volume cubed-sphere model with a full physics package and a lower-resolution (300–100 km) hydrostatic spectral model with idealized moist physics. Despite differences in their physics and numerics, both models demonstrate that column-integrated poleward moist static energy transport by the mean meridional circulation increases with resolution in the deep tropics, while transport by transient eddies decreases. These changes are associated with enhanced gross moist stability that switches from negative to positive due to an increasingly top-heavy mean circulation and reduced eddy activity diffusing water vapor along an unchanging mean moisture gradient. Further analysis rules out extratropical baroclinic eddies and radiation as the main drivers of these changes. Instead, the resolution dependence of both the mean meridional circulation and transient eddies appears to reflect the resolution dependence of tropical explicit (unparameterized) deep convection. We speculate the multiscale interactions of convection allow for a coupling between gross moist stability and eddy moisture flux, leading to their concurrent changes with resolution. We discuss the implications of this resolution dependence for developing theories and models of the tropical atmosphere.
How to cite: Chang, C.-Y., Lin, P., Held, I., Merlis, T., and Zurita-Gotor, P.: Resolution Dependence of Tropical Poleward Energy Transport in Aquaplanet GCMs, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3869, https://doi.org/10.5194/egusphere-egu26-3869, 2026.
Earth system models are widely used to make projections not only about the mean atmospheric state under climate warming, but also about the circulation on synoptic to seasonal timescales and their related weather extremes. However, the statistics and characteristics of synoptic weather systems, such as extratropical cyclones, exhibit substantial biases relative to observations and reanalysis data. Although model resolution and the representation of moist processes have been pinpointed as important contributors to these biases, the exact pathway by which they affect the cyclone evolution and the coupling between the surface and upper-level flow needs further investigation.
Here, we present a spectral analysis that reveals pronounced biases in the extratropical upper-level kinetic energy, especially at the upper end of synoptic scales, when comparing Community Earth System Model version 2 large ensemble simulations (CESM2-LENS) to ERA5. Focusing on the North Pacific storm track, we show that upper-level eddy kinetic energy (EKE) is underestimated by up to 30% and upper-level forcing as measured by QG omega forcing is reduced in CESM2. In addition, we observe differences in the vertical structure of diabatic heating between CESM2 and ERA5. CESM2 exhibits weak and permanent heating in the planetary boundary layer, whereas ERA5 shows more intermittent, localised heating that extends further into the free troposphere. We discuss possible relationships between these biases and cyclone properties in the North Pacific storm track. This provides a pathway by which model biases in both the upper and lower levels can influence the structure and evolution of extratropical cyclones, potentially amplifying upper-level errors.
How to cite: Zilibotti, N., Wernli, H., and Schemm, S.: An in-depth analysis of the North Pacific storm track bias in CESM2-LENS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13451, https://doi.org/10.5194/egusphere-egu26-13451, 2026.
Wintertime variability of both the strength of the jet stream and the North Atlantic Oscillation (NAO) index are known to be significantly correlated on the decadal scale and have positive trends since the 1960s which have been recently proposed to be connected to anthropogenic global warming (Blackport and Fyfe, 2022). At the same time there is a rich literature explaining both the observed variability and also the discrepancy with circulation models in which the variability is usually much smaller. The North Atlantic sector is known to be the nexus of the so called signal-to-noise paradox in climate modelling (Scaife and Smith, 2018) with models underestimating the interdecadal variability in both atmospheric circulation (NAO) and ocean temperatures (AMO/AMV) by an order of magnitude Smithe et al. 2020.
Scaife and Smith (2018) offer a selection of possible lacking processes causing this problem: (“lack of extratropical ocean–atmosphere coupling, weak eddy feedback in current resolution models, errors in remote teleconnections, or errors in parameterized processes such as atmospheric convection”. On the other hand, it is well known that the pattern of SST values on the North Atlantic and the position of the Gulf Stream affect the value (and sign) of wintertime NAO (Hermoso et al. 2024). The covariation of the jet stream strength and NAO on the decadal time scale seen in observation data suggests that this coupling may be one of the most important missing factors, however the phenomenon itself may be too weak in the models, which is one of the hypotheses to be tested.
This study tries is a first step in trying to find spatial patterns of differences in decadal-scale variability of atmospheric circulation at different altitudes in the Atlantic sector between (observation data assimilating) climate reanalyses and (non-assimilating) CMIP 5 & 6 runs The aim is to pinpoint where and how they differ. This presentation shows the preliminary results of such analysis.
How to cite: Piskozub, J.: Is the coupling of the jet stream strength in the Atlantic sector and NAO too weak in the circulation models?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7965, https://doi.org/10.5194/egusphere-egu26-7965, 2026.
The Late Pliocene (3 million years ago) is the last period of sustained warmth characterised by elevated carbon dioxide (~400 ppmv), smaller ice sheets and warmer temperatures (~3.2°C above pre-industrial), with a similar to modern continental configuration. This period gives us an insight into how the climate system behaves in a warmer than present state. The majority of research on the Late Pliocene focuses on long term mean states, but examining variability and extreme events provides a deeper understanding of the response of the climate to different forcings, and how these changes are captured across different climate models.
Here, we present an overview atmospheric circulation in the North Atlantic in the Late, including changes to the jet stream and the North Atlantic Oscillation (NAO).
We use data from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2), a multi-national modelling effort consisting of 17 climate models. We find that the NAO tends towards a more positive phase of the NAO and this shift can explain the mean state precipitation pattern change observed in the PlioMIP2 ensemble. We investigate the drivers of the change using the Hadley Centre Coupled Climate Model, Version Three (HadCM3) to separate out the impacts of Pliocene CO2, orography and ice sheets on the NAO.
This work highlights the benefit of using past climates to improve understating of the climate system and shows the need to consider a multi-model, multi-centennial viewpoint when examining higher frequency variability in past climates.
How to cite: Buchan, A., Haywood, A., Dolan, A., Tindall, J., and Hill, D.: North Atlantic variability in a warmer world: what can the Pliocene tell us?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5314, https://doi.org/10.5194/egusphere-egu26-5314, 2026.
The Pliocene Model Intercomparison Project (PlioMIP) provides model ensemble results to various forcings associated with the Pliocene. Here we investigate the response in the Southern Hemisphere of the large-scale climate features in the PlioMIP3 ensemble, e.g. the strength of the Hadley Cell, changes in the westerly winds, and possible mechanisms for their response, e.g. increased stability in the atmosphere, changes in convection sites, and ocean temperature anomaly response, for instance. In addition, the interconnection between features is explored. With PlioMIP at (or nearing) the end of its submission stage for phase three (PlioMIP3) this presentation will provide a first look at the response in the Southern Hemisphere, comprising the tropics through to the mid-latitudes.
How to cite: Gravis, P., Brown, J., Stepanek, C., and Drysdale, R.: Simulated Southern Hemisphere Response in the PlioMIP3 Ensemble: A Preliminary Analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15850, https://doi.org/10.5194/egusphere-egu26-15850, 2026.
Internally inconsistent approximations made in the Community Atmosphere Model result in local violation of energy conservation to the rate of several hundreds of TW when integrated globally, comparable to the total power currently absorbed by the entire observed Earth System -- not just the atmosphere, which is probably absorbing about 1 TW.
This problem, which is not unique to CAM among CMIP-class atmosphere models, may cast doubts on its use for current projections of climate change.
Fortunately, once understood, it is easily resolved.
We show how, and compare simulations with good energy conservation with those currently used in CMIP7 integrations to clarify the impact of non-conservation on the results.
How to cite: Toniazzo, T.: Local and global energy conservation in the Community Atmosphere Model (CAM), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11503, https://doi.org/10.5194/egusphere-egu26-11503, 2026.
Vertical wind structure plays a central role in tropospheric dynamics, yet its variability is rarely characterized beyond surface-level fields. Summarizing this variability over multi-decadal timescales requires reducing the dimensionality of wind profiles while preserving their dynamical content. Here, we develop an objective classification of vertical wind regimes using the ERA reanalysis (1940–2024), to identify a compact set of representative tropospheric structures and quantify their temporal evolution.
We first derive spatio-temporal averaged wind profiles from the reference regions defined within the IPCC framework. Although these regions are based on surface climate characteristics, the resulting regional wind profiles provide a baseline against which we compare new wind profile classifications from vertical climate variability.
Dominant modes of variability are extracted using empirical orthogonal functions applied to multi-level wind profiles. Clustering (k-means and hierarchical approaches) is then performed in the reduced phase space to identify dynamical regimes, with robustness assessed through bootstrap resampling and multiple validation metrics. We show that a limited number of regimes capture most of the tropospheric wind variance over the 84-year period, each characterized by distinct vertical shear and directional signatures. The length of the record allows us to examine persistence, transition probabilities, and modulation across seasonal to multi-decadal variability.
Overall, this framework provides a physically interpretable compression of vertical wind variability over a uniquely long ERA dataset, offering new diagnostic tools for atmospheric dynamics and a potentially valuable input for transport, dispersion, and predictability studies.
How to cite: Goursaud Oger, S.: A robust classification of tropospheric wind profiles from ERA reanalyses (1940–2024), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5049, https://doi.org/10.5194/egusphere-egu26-5049, 2026.
Understanding how jet streams respond to a warming climate is crucial for anticipating changes in atmospheric circulation and their broader impacts. Previous studies have highlighted the influence of anthropogenic warming on the meridional temperature gradient, which directly affects jet stream dynamics and variability. This study investigates projected trends in upper-level jet stream shear instability under future climate change scenarios using CMIP6 multi-model simulations. Building on previous findings linking anthropogenic warming to strengthened meridional temperature gradients, we analyse annual means of zonal wind speed, vertical wind shear, and stratification profiles from 2015 to 2100 globally. Results show strengthened multi model annual-mean vertical shear at 250 hPa, particularly in high-emission scenarios, with trends ranging from 0.04 to 0.11 m s⁻¹ (100 hPa)⁻¹ decade⁻¹ depending on the scenario, and region (a total relative increase of 16 - 27% over 86 years). Decreasing trends are observed in the annual-mean Brunt-Väisälä frequency (N²) at 250 hPa, with multi-model ensemble mean values across regions ranging from -0.018 to -0.040 × 10⁻⁴ s⁻² decade⁻¹ for lower and higher emissions scenarios, respectively (a total relative decrease of -10 to -20%). Similarly, the Richardson number (Ri) shows decreasing trends of -0.014 to -0.050 decade⁻¹ across emissions scenarios and regions (a total relative decrease of -38 to -47%). These findings suggest an increased likelihood of more favourable conditions for stronger and more frequent Clear-Air Turbulence (CAT), posing critical challenges for aviation safety and operations in a warming climate.
How to cite: Medeiros, J. and Williams, P.: Future Trends in Upper-Atmospheric Shear Instability from Climate Change, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-508, https://doi.org/10.5194/egusphere-egu26-508, 2026.
Turbulence is the principal cause of in-flight bumpiness at cruise level, causing economic loss and threatening passenger safety. Following the growth of aviation transport, the impact of turbulence has become critical, making it necessary to investigate its response to climate change. This study will examine the historical frequencies of near-cloud turbulence (NCT), which is difficult to avoid because it is invisible to radar and satellites. Previous research has been scarce because cloud boundaries are ill-defined and multiple influencing mechanisms are involved. In this study will use the latest ERA5 reanalysis (1979-2024) and a dedicated parameterization. We examine global NCT climate trends across seven regions, four diagnostics, five turbulence-intensity bins and four seasons. At typical cruise altitudes, diagnosed NCT probabilities have risen in the mid-latitudes, most notably along heavily trafficked corridors over Europe, the North Atlantic, the North Pacific, and the south-western United States, with local relative increases reaching 100%. Conversely, probabilities have fallen in the tropics—especially over long-standing hotspots such as Southeast Asia and the Caribbean Sea. A lower occurrence rate, however, may signal fewer but deeper and more vigorous convective events, increasing the risk to commercial aviation. These findings in the tropics differ from earlier climate-model projections and should help refine future NCT forecasts, providing a fuller basis for assessing aviation exposure in a warming climate.
How to cite: Lin, C. and Williams, P.: Past trends in near-cloud turbulence diagnosed from reanalysis data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19328, https://doi.org/10.5194/egusphere-egu26-19328, 2026.
Upper tropospheric water vapour plays a crucial role in the climate system by providing a strong positive feedback, particularly in the tropics. Upper Tropospheric Humidity (UTH) is strongly linked to large-scale atmospheric circulation, including the Hadley and Walker circulations, which undergo pronounced modulation during El Niño–Southern Oscillation (ENSO) events. In this study, we examine ENSO-related changes in the tropical distribution of UTH using long-term climatological datasets of UTH and sea surface temperature (SST). Significant upper-tropospheric drying (moistening) during El Niño (La Niña) years is observed over the Maritime Continent, the western Pacific, and the Indian subcontinent. These UTH anomalies are accompanied by corresponding negative (positive) anomalies in precipitation and upper-level cloud fractions, indicating a strong coupling between UTH and tropical convection. However, the statistical significance of these signals over the Indian subcontinent is limited, suggesting that ENSO influences UTH over India indirectly, likely mediated by regional circulation and monsoon dynamics. Overall, our results highlight ENSO as a key driver of tropical UTH variability through its impact on atmospheric circulation and convection.
How to cite: Moovidathu Vasudevan, D., Kottayil, A., and O John, V.: The Role of ENSO in Modulating the Tropical Upper Tropospheric Humidity, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16173, https://doi.org/10.5194/egusphere-egu26-16173, 2026.
The accelerated warming of the Arctic relative to the rest of the globe has sparked ongoing debate about its influence on Northern Hemisphere atmospheric circulation. Many studies suggest that this warming may alter large-scale circulation through changes in temperature gradients, storm tracks, and planetary wave dynamics. From a weather regime perspective, which describes preferred and recurrent large-scale circulation patterns, this study investigates the projected changes in Northern Hemisphere atmospheric circulation across different seasons. First, the ability of CMIP6 models to reproduce observed circulation regimes is evaluated against ERA5 reanalysis. We then assess the projected response of these regimes under climate change scenarios in terms of their frequency of occurrence and persistence. The analysis focuses on mean sea level pressure and applies a physically informed convolutional autoencoder combined with k-means clustering. This data-driven climate classification workflow uses unsupervised deep learning to reduce the dimensionality of spatiotemporal climate simulation data into compact representations.
Results show that CMIP6 models generally reproduce the main Northern Hemisphere circulation patterns and their seasonal behavior, particularly in winter and spring, although performance varies among models. The ensemble mean slightly underestimates the amplitude of mean sea level pressure anomalies in all seasons, most notably in summer. Despite this bias, the main circulation patterns and their seasonal characteristics are reasonably well reproduced. Based on this present-day evaluation, projections toward the end of the twenty-first century indicate that changes in regime frequency are stronger and more robust under SSP5-8.5. Zonal regimes, such as the NAO+ pattern, as well as regimes associated with negative pressure anomalies over the Arctic, tend to become more frequent, in agreement with previous studies, while blocking regimes exhibit a systematic decline under warming. Finally, the weather regime framework provides the basis for an ongoing investigation of the associated impacts of projected circulation shifts on the regional climate system.
How to cite: bizdaz, A., Jacobi, C., Handorf, D., and Mehrdad, S.: Projected Changes in Northern Hemisphere Weather Regimes Using a Deep Learning–Based Classification Approach, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7616, https://doi.org/10.5194/egusphere-egu26-7616, 2026.
This study examines the large-scale circulation and thermodynamic anomalies associated with extreme air pollution events over India using a composite analysis based on detrended PM₂.₅ data. High- and low-pollution episodes are identified from monthly anomalies in near-surface air quality, and composites are constructed to reveal consistent dynamical and thermodynamic patterns. During high-pollution periods, anomalous upper-tropospheric anticyclonic circulation and positive height anomalies are observed, accompanied by suppressed vertical motion and warming, which inhibit ventilation and favor pollutant accumulation. In contrast, low-pollution events exhibit enhanced upper-level divergence, stronger ascent, and cooling throughout the troposphere, supporting efficient dispersion and wet removal of aerosols. The divergence and vertical velocity fields highlight the role of weakened overturning circulation and reduced convection in modulating stagnant conditions. Analysis of moist static energy (MSE) further distinguishes polluted and clean regimes: elevated MSE during high-pollution periods indicates enhanced stability and reduced convective potential, while lower MSE during cleaner phases reflects greater instability and active vertical exchange that promotes pollutant removal. At the surface, positive sea-level pressure anomalies and weakened low-level winds limit horizontal ventilation, whereas negative pressure anomalies and intensified winds enhance dispersion. Overall, the results highlight that large-scale circulation and thermodynamic variability strongly modulate monthly air pollution extremes over India. The detrended composite effectively isolates meteorological drivers, offering clearer insight into the processes governing severe pollution episodes.
How to cite: Dwivedi, A. and Mishra, S. K.: Meteorological Controls on Air Pollution in India, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7676, https://doi.org/10.5194/egusphere-egu26-7676, 2026.
