Hadley Circulation Variability in Climate Systems

The Hadley circulation is the dominant meridional overturning of the atmosphere in tropical and subtropical latitudes, linking the equatorial ascent of warm, moist air to subsidence in the subtropics. Variability in its strength, width and seasonal position exerts a profound influence on the location of the subtropical dry zones, the intertropical convergence zone and the global hydrological cycle. Observations and reanalyses reveal interannual fluctuations tied to modes such as El Niño–Southern Oscillation and the Arctic Oscillation, while palaeoclimate reconstructions and millennial‐scale model experiments demonstrate the imprint of natural forcings on centennial trends. Under anthropogenic warming, there is robust evidence for a poleward expansion of the circulation edges, accompanied by a general weakening of overturning mass flux. However, the magnitude and hemispheric asymmetry of these changes remain uncertain owing to model spread in equilibrium climate sensitivity and biases in eddy–mean‐flow interactions. The coupling between tropical and extratropical regions through eddy momentum fluxes and baroclinic processes further complicates the response. Improved representation of natural forcings, cloud–radiation feedbacks and momentum transfer is essential to constrain future shifts in rainfall patterns, subtropical aridity and tropical cyclone genesis regions.

Research from Nature Portfolio

Recent studies have simulated the countervailing effects of natural and anthropogenic forcings on the Northern Hemisphere Hadley cell. State-of-the-art climate models indicate that while natural forcings over the past millennium would have intensified the circulation through cooling, historical and projected greenhouse-gas emissions have reversed this trend, leading to unprecedented weakening. Another investigation has classified meridional overturning regimes using isentropic diagnostics and observed that the frequency of short-term circulation patterns has shifted over recent decades. These shifts coincide with stratospheric ozone depletion and reveal a coupling between boreal and austral winter circulations, suggesting that changes in regime occurrence may underpin long-term atmospheric trends.

Research from all publishers

A reanalysis-based study has elucidated the physical chain leading to interannual variations in the Hadley cell edge, identifying transient and stationary eddy momentum flux divergences as primary drivers and attributing substantial variance to El Niño–Southern Oscillation and the Arctic Oscillation. Projections constrained by the latest model intercomparison reveal that uncertainty in equilibrium climate sensitivity accounts for much of the spread in future weakening and poleward expansion; applying an emergent-constraint approach reduces projected changes by roughly 15 % in strength and 11 % in edge shift under high-emission scenarios. A comprehensive review of observed and simulated trends confirms a widening of the circulation over recent decades but highlights persistent discrepancies in strength trends across reanalyses and models, underscoring the need to reconcile methodological biases and natural variability on centennial timescales.

Hadley Circulation Variability in Climate Systems publication trend

The graph below shows the total number of articles in hadley circulation variability in climate systems across all publications each year (not limited to Nature Index journals).

Technical terms

Hadley circulation: The tropical–subtropical overturning cell that transports heat and moisture from the equator to subtropical latitudes.

Eddy momentum flux divergence: The net transfer of momentum by atmospheric waves, altering the mean flow and influencing circulation edges.

Baroclinicity: A measure of horizontal temperature gradients that drive atmospheric instability and eddy generation.

Equilibrium climate sensitivity (ECS): The global mean temperature change resulting from a doubling of atmospheric CO₂ concentration.

Intertropical Convergence Zone (ITCZ): The equatorial belt of convective ascent and converging trade winds, crucial to tropical rainfall distribution.

References

1. Anthropogenic forcings reverse a simulated multi-century naturally-forced Northern Hemisphere Hadley cell intensification. Nature Communications (2024).
2. Atmospheric trends explained by changes in frequency of short-term circulation patterns. Communications Earth & Environment (2023).
3. What controls the interannual variation of Hadley cell extent in the Northern Hemisphere: physical mechanism and empirical model for edge variation. npj Climate and Atmospheric Science (2023).
4. Recalibrated projections of the Hadley circulation under global warming. Environmental Research Letters (2024).
5. Widening and weakening of the Hadley circulation under global warming. Science Bulletin (2018).