Storm tracks, the preferred highways along which extratropical cyclones and their attendant wind, rain and temperature swings travel, are among the most consequential features of the climate system. They regulate weather variability and extremes throughout the midlatitudes of both hemispheres, yet climate models still struggle with stubborn biases in their strength and location, and emerging discrepancies have appeared between simulated and observed storm track trends in some regions. That makes a return to first principles, asking which parts of Earth’s uneven surface actually build the storm tracks we observe, both timely and practical.

The team attacked the problem using MiMA, the Model of an idealized Moist Atmosphere, an intermediate-complexity general circulation model that bridges the gap between stripped-down aquaplanet experiments and fully comprehensive climate models. Crucially, MiMA carries full radiative transfer through the Rapid Radiative Transfer Model, a physically consistent treatment of moisture transport and latent heat release, and a slab ocean with prescribed ocean heat fluxes. That combination allowed the researchers to switch Earth-like land–sea contrast, topography and ocean heat transport on and off in any combination, an experiment that no single comprehensive model could perform cleanly, since in the real world it is difficult to imagine mountains without land or ocean circulation without continents.

The authors ran a suite of eight core configurations, each lasting 38 years after spin-up, beginning with a perfectly zonally symmetric aquaplanet and building up to a realistic ALL3 configuration containing all three surface inhomogeneities. By comparing each partial configuration with the full one, they could isolate both the isolated nonlinear response of a single ingredient, added first onto an aquaplanet, and its full nonlinear response, added last to a world that already had the other two. In parallel, they updated the model’s prescribed albedo profile to match satellite observations from CERES and revised the implied ocean heat transport so that the net flow of heat from the Southern Hemisphere to the Northern Hemisphere reached 0.54 petawatts, in line with observationally derived estimates, up from just 0.24 petawatts in the earlier configuration.

The realism check was encouraging. When all three ingredients were switched on, the model reproduced the observed pattern of storm tracks, with peaks over the North Pacific, the North Atlantic and the Indian-Ocean sector of the Southern Ocean, although the North Pacific came out somewhat too strong, the North Atlantic somewhat too weak, and the finer zonal structure of the Southern Hemisphere storm track was only fully captured at the higher T85 resolution. With the earlier albedo and ocean-flux settings, storm tracks had been 17 percent too weak at T85 and 29 percent too weak at T42; the updated configuration brought that bias down to 7 percent at T42 and essentially eliminated it at T85.

The central result concerns additivity. If the climate system were linear, the storm tracks in the full realistic configuration would equal the sum of the responses to land, mountains and ocean heat transport imposed individually. They do not. The team found substantial non-additivity both in the regional structure of the storm tracks and in the hemispheric asymmetry. Adding all three inhomogeneities reduces transient kinetic energy everywhere, partly because more energy is handed off to stationary waves forced by the uneven surface, and partly because realistic ocean heat transport carries some of the poleward energy load that transient eddies would otherwise shoulder. But the size of that effect depends dramatically on the order of assembly. In most sectors, the impact of the surface inhomogeneities is magnified when they are imposed on an aquaplanet compared with when they are removed from the full configuration, and the regional signature of ocean heat transport flips qualitatively between the two, weakening storm tracks most strongly over Eurasia when added first but over the North Pacific and North Atlantic when added last.

The same story holds for the headline asymmetry: in the full configuration the model’s Southern Hemisphere storm tracks are roughly 48 percent stronger than the north’s when measured with 2-to-8-day filtered transient kinetic energy, and about 25 percent stronger with a sub-monthly filter, broadly consistent with the observed excess of about 23 to 24 percent in the moist static energy framework applied to ERA5 reanalysis. Yet the sum of the isolated responses of the three ingredients accounts for only half of that asymmetry, while the sum of the full nonlinear responses overshoots it by 30 percent. Among the individual ingredients, land–sea contrast emerges as the most important driver of the hemispheric asymmetry, followed by ocean heat transport, with topography a distant third, a ranking that challenges earlier conclusions from comprehensive models in which topography and ocean circulation dominated.

To explain the mechanisms, the authors turn to the atmospheric moist static energy budget, decomposing poleward heat transport into contributions from the ocean, the mean meridional circulation, stationary eddies and transient eddies. In the realistic configuration, the surface energy input term, reflecting the ocean’s preferential delivery of heat to the Northern Hemisphere extratropics, contributes about 15.6 percentage points to the hemispheric asymmetry, while the stationary eddy term contributes 22.4 points, partially offset by a top-of-atmosphere term of minus 5.2 points. A striking simplification emerges when the researchers examined outgoing longwave radiation: across all 21 simulations, the correlation between the hemispheric asymmetry in longwave emission and the asymmetry in surface temperature was 0.99, meaning surface temperature essentially dictates how much energy the planet radiates to space in each hemisphere. Ocean heat transport and topography both preferentially cool the Southern Hemisphere, warming the north and increasing its longwave loss, which partially cancels their own intensifying effect on the asymmetry; land–sea contrast, by contrast, preferentially cools the north, deepening the asymmetry.

Two sensitivity experiments underline how delicate these balances are. Boosting the implied Southern-Ocean-to-North-Atlantic heat transport from 0.54 to 0.74 petawatts, a shift well within observational uncertainty, produced dramatic cancellations: transient eddy heat transport in the north actually increased by 0.34 petawatts rather than decreasing, because the stationary eddy term weakened by nearly the same amount, even as the North Atlantic storm track intensified locally. Likewise, tweaking midlatitude albedo over Northern Hemisphere land and ocean produced compensating changes in absorbed shortwave and emitted longwave radiation, leaving the hemispheric asymmetry nearly untouched despite pronounced regional shifts. The authors caution that MiMA lacks radiatively active clouds, whose treatment differs widely across climate models, and that its overly strong stationary eddy asymmetry may inflate the apparent importance of land–sea contrast. Even so, the message is clear: storm tracks cannot be understood ingredient by ingredient. Each piece of Earth’s patchwork surface sets the background state on which the others act, and that entanglement may be precisely why climate models, with their differing ocean heat transports and cloud biases, still disagree about where and how strongly the planet’s storms will rage in a warming world.

Subject of Research: How land–sea contrast, ocean heat transport and topography shape the localization and hemispheric asymmetry of midlatitude storm tracks

Article Title: Building blocks of localized storm tracks: revisiting asymmetries between the NH and SH in storm track strength

Article References: Garfinkel, C. I., Shaw, T., Keller, B., Gerber, E. P., White, I. P., Jucker, M., Ning, W., Adam, O., & Liu, S. (2026). Building blocks of localized storm tracks: revisiting asymmetries between the NH and SH in storm track strength. Weather and Climate Dynamics, 7(4), 1951-1975. https://doi.org/10.5194/wcd-7-1951-2026

Image Credits: AI Generated

DOI: 10.5194/wcd-7-1951-2026

Keywords: storm tracks, midlatitude cyclones, land-sea contrast, ocean heat transport, topography, stationary waves, transient eddies, moist static energy budget, general circulation model, hemispheric asymmetry, albedo, climate modeling

The research, led by Shanshan Fu of Nanjing University of Information Science and Technology and the Dalian Meteorological Observatory, together with Zhiwei Zhu and Xiao Pan of the Ocean University of China and the Max Planck Institute for Meteorology, analyzed observational and reanalysis data spanning 1961 to 2024. The team identified three clearly separated phases in how the tripole relates to springtime surface air temperature across the Eurasian and North African landmass. In the first phase, from 1961 to 1986, a positive tripole, meaning warmer water in the subtropical and subpolar North Atlantic flanking a cooler band in between, produced warming over North Africa, the Middle East and the Indo-China Peninsula, along with cooling over Northern Europe. Those were the days when the tripole could be counted on as a reliable seasonal clue.

Then came the middle chapter. Between 1987 and 2005, the subtropical temperature responses largely collapsed. The warming signals over North Africa and the Middle East faded to statistical insignificance, while the cooling over Northern Europe stubbornly persisted. Forecasters and researchers who had built seasonal expectations on the tripole’s influence suddenly found the connection unreliable over much of the affected domain. In the third phase, from 2006 to 2024, the story shifted again: the warming over North Africa re-emerged, but a new and significant cooling signal appeared over Northeast Asia, a region that had not featured prominently in the tripole’s earlier influence map. The pattern, in other words, did not simply strengthen or weaken. It changed its geography.

What could cause a fixed oceanic pattern to reshuffle its downstream fingerprints so dramatically? The authors point to the propagation pathways and structures of the Rossby wave trains that the tripole excites. When sea surface temperature anomalies alter the heating of the overlying atmosphere, they launch planetary-scale waves that arc across the midlatitudes like ripples guided along a curved channel. Where those waves deposit their energy determines which regions warm and which cool. If the wave train takes a more zonal track hugging the subtropics, North Africa and the Middle East feel the effects. If it arcs poleward into higher latitudes, Europe and Northeast Asia come into play. The tripole provides the push, but the atmosphere decides where the push lands.

The decisive factor, according to the study, is the background mean zonal wind, essentially the prevailing east-west flow of the atmosphere through which the waves must travel. Rossby waves do not propagate through a static medium; their trajectories, group velocities and amplitudes depend on the structure of the ambient flow, particularly the position and strength of the jet streams that act as waveguides. When the background zonal wind shifts, the wave train bends with it, and the regions of wave-activity flux convergence, where the teleconnection’s temperature anomalies are ultimately expressed, migrate accordingly. The three phases identified in the observations correspond to three configurations of this mean flow, each steering the tripole’s atmospheric response along a different route.

The study goes one step further by asking what drives the mean flow changes themselves. The authors identify two contributors: intensified local transient-eddy activity and shifted tropical convection anomalies. Transient eddies, the swirling synoptic-scale disturbances that populate the storm tracks, exert a feedback on the time-mean flow, and changes in their intensity can reinforce or reshape the zonal winds. Meanwhile, shifts in tropical convection, the towering organized thunderstorm systems of the deep tropics, can alter the large-scale circulation remotely, nudging the midlatitude flow into a new configuration. Either pathway, operating in different phases, sufficed to explain the observed changes in the background winds that steered the wave trains.

To test whether these mean-flow changes were truly sufficient, rather than merely correlated, the team turned to a linear baroclinic model, a simplified numerical tool designed to isolate the role of the background flow in wave propagation. By imposing the observed mean-flow conditions from each phase and forcing the model with the tripole’s atmospheric signature, they found that the model reproduced the phase-dependent Rossby wave trajectories seen in the real atmosphere. The observed changes in the mean flow alone were enough to recreate the shifting pathways, without needing to invoke changes in the tripole itself. This result elevates the background mean flow from a plausible suspect to the key mechanism: it is the control knob that determines how the ocean’s influence is distributed across the continents.

The findings carry practical weight for seasonal climate prediction. Spring surface air temperature over Eurasia and North Africa affects agriculture, water resources, snowmelt timing and the likelihood of temperature extremes, and forecasters have long used North Atlantic sea surface temperature anomalies as precursors. A teleconnection relationship that holds in one decade may fail in the next, and this study explains why: the relationship is conditional on the state of the background flow, which evolves on interdecadal timescales under the influence of eddy activity and tropical convection. Skillful use of the tripole as a predictor therefore requires monitoring not just the ocean, but the atmospheric highway that carries its signal eastward.

More broadly, the work adds to a growing recognition that climate teleconnections are not fixed features of the Earth system but dynamic relationships that drift as the background circulation evolves. Similar interdecadal changes have been documented for other ocean-atmosphere links, including the influence of the tripole on the western North Pacific subtropical high and on East Asian rainfall, suggesting that the mean-flow modulation mechanism may be a general property of midlatitude teleconnections. As greenhouse warming continues to alter jets, storm tracks and tropical convection, the map of which regions are teleconnected to which ocean basins may keep redrawn itself. The tripole has not lost its voice; the atmosphere has simply changed the rooms in which it can be heard.

Subject of Research: How changes in background mean flow modulate the influence of the North Atlantic tripole sea surface temperature pattern on springtime surface air temperature over Eurasia and North Africa

Article Title: Changing influence of the North Atlantic tripole SST pattern on surface air temperature in Eurasia and North Africa modulated by the background mean flow

Article References: Fu, S., Zhu, Z., & Pan, X. (2026). Changing influence of the North Atlantic tripole SST pattern on surface air temperature in Eurasia and North Africa modulated by the background mean flow. Climate Dynamics, 64(10), Article 429. https://doi.org/10.1007/s00382-026-08391-x

Image Credits: AI Generated

DOI: 10.1007/s00382-026-08391-x

Keywords: North Atlantic tripole, sea surface temperature, surface air temperature, Rossby wave train, background mean flow, Eurasia, North Africa, teleconnection, Climate Dynamics, jet stream, transient eddies, spring climate

The research team, led by Feyisa Seboka Tura of the Institute of Atmospheric Physics at the Chinese Academy of Sciences, together with colleagues including Jinling Piao, Lin Wang, and Wen Chen, analyzed more than four decades of atmospheric data from 1981 to 2024. They combined the ERA5 global reanalysis produced by the European Centre for Medium-Range Weather Forecasts — a physically consistent reconstruction of winds, humidity, and temperature across the entire atmosphere — with satellite-derived rainfall products. This pairing allowed them to close the atmospheric moisture budget over Ethiopia with a rigor that earlier studies, which often relied on shorter records or single data streams, could not achieve.

The study’s central technical move is the decomposition of the vertically integrated moisture flux into two parts: a stationary component, representing the climatological, time-averaged circulation, and a transient component, capturing departures from that mean on daily to weekly timescales. When the two are evaluated over Ethiopia’s three rainfall seasons — the Belg rains from February to May, the Kiremt monsoon from June to September, and the dry-season Bega window from October to January — a striking asymmetry emerges. The stationary flux alone closely reproduces the net moisture convergence and the observed pattern of precipitation across the country. In other words, the steady background flow of the atmosphere explains most of where and when Ethiopia’s rain falls.

Geographically, the dominant inflow is meridional: moisture arrives primarily across Ethiopia’s southern boundary, funneled from the Indian Ocean and from the Congo Basin deep in equatorial Africa. Two celebrated circulation systems do much of the heavy lifting. The Somali Jet, the low-level cross-equatorial wind that races along the East African coast during the boreal summer, carries enormous quantities of Indian Ocean vapor northward. It is reinforced by the broader cross-equatorial low-level flow that pulses across the equator with the march of the seasons. Together, these currents supply the raw water vapor that the Ethiopian highlands, lifted and cooled by their dramatic topography, convert into some of the heaviest orographic rainfall in Africa.

The transient component tells a very different and, in some respects, counterintuitive story. On average, the transient moisture fluxes are climatologically divergent: rather than feeding rain, they tend to export moisture and weaken the net convergence that the stationary circulation establishes. The eddies, waves, and short-lived disturbances that dominate weather maps do not, in the climatological mean, add to Ethiopia’s water supply — they subtract from it, acting as modulators of short-term variability rather than as the foundational source of rain.

Perhaps the most surprising result concerns wet Kiremt years — the seasons when Ethiopia’s summer monsoon delivers abundant rainfall. One might assume that in such years the Somali Jet strengthens and drives extra moisture inland. The analysis reveals the opposite. During anomalously wet Kiremt seasons, transient moisture transport is associated with an anticyclonic circulation anomaly over the Arabian Sea and a weakened Somali Jet. This configuration generates an enhanced anomalous easterly flow that pushes moisture away from the region, producing significant divergence. The wettest summers are therefore not simply the result of stronger moisture import; they reflect a delicate balance in which the stationary convergence strengthens even as transient processes actively drain moisture, a subtlety that coarse analyses of total moisture flux would entirely miss.

To probe interannual variability, the team constructed composites of wet and dry years across the 44-year record. The comparison shows that year-to-year swings in Ethiopia’s moisture convergence are largely tied to anomalies in the stationary circulation itself — shifts in the position and strength of the mean low-level inflow — while transient eddies act mainly as secondary modifiers. The study further links these stationary anomalies to tropical-extratropical teleconnections, the planetary-scale wave trains through which conditions in distant ocean basins, such as the tropical Indian Ocean and its dipole mode, imprint themselves on East African circulation. This places the new results in dialogue with a long lineage of research connecting Ethiopian rainfall to global sea surface temperatures, El Niño-Southern Oscillation variability, and the intensification of the Walker circulation, but it sharpens the mechanism by translating those remote forcings into concrete changes in moisture flux convergence.

The implications for prediction are substantial. Seasonal forecasting of the Kiremt rains has long been a priority for Ethiopian agriculture, and models such as ECMWF’s SEAS5 are already used to anticipate monsoon anomalies. The new decomposition offers forecasters a diagnostic target: rather than attempting to predict the behavior of fast-moving eddies, which are inherently chaotic and difficult to anticipate months in advance, forecast skill should focus on the stationary circulation — the cross-equatorial flow, the Somali Jet, and the large-scale convergence patterns that dominate the moisture budget. Because the stationary component is more strongly constrained by slowly varying boundary conditions like sea surface temperatures, it is more predictable, meaning the study effectively identifies where forecast value can be won.

The work also carries a sobering message for a warming century. Ethiopia has endured repeated devastating droughts, including the recurrent East African dry spells of recent decades, and projections consistently indicate changes in rainfall extremes and agro-climatic zones across the region. By establishing that persistent large-scale transport is the backbone of the nation’s hydroclimate, the study suggests that future shifts in the Indian Ocean and in global monsoon circulations will propagate directly into Ethiopia’s water security through the stationary flux. Monitoring and modeling that persistent circulation, rather than the noise of daily weather, may be the clearest window into the country’s climatic future — and a lifeline for the farmers who depend on it.

Subject of Research: Atmospheric moisture transport and rainfall variability over Ethiopia

Article Title: Roles of atmospheric moisture transport in seasonal and interannual variations of rainfall over Ethiopia

Article References: Tura, F. S., Piao, J., Wang, L., Wang, Z., Cai, Q., Yu, T., & Chen, W. (2026). Roles of atmospheric moisture transport in seasonal and interannual variations of rainfall over Ethiopia. Climate Dynamics, 64(10), Article 424. https://doi.org/10.1007/s00382-026-08379-7

Image Credits: AI Generated

DOI: 10.1007/s00382-026-08379-7

Keywords: Ethiopia, moisture transport, Somali Jet, Kiremt rainfall, ERA5 reanalysis, moisture convergence, Climate Dynamics, East African monsoon, transient eddies, seasonal forecasting, drought, Indian Ocean