The Atlantic Multidecadal Oscillation (AMO) stands as one of the most compelling influences on climate variability, affecting vast regions of the Northern Hemisphere including North America, Europe, and Asia. Characterized by alternating warm and cool phases in the Atlantic Ocean surface temperature recurring every 40 to 80 years, the AMO impacts not only weather patterns such as hurricane frequency and heatwaves but also marine ecosystems like the migratory routes of Atlantic bluefin tuna. Despite its profound implications on both natural systems and human societies, the exact mechanisms that drive the AMO have eluded scientific consensus for decades.
Recent advances in high-resolution climate modeling have begun to peel back the layers of this complex ocean-atmosphere interplay. Yet, until now, the precise reason that finer model resolutions improve AMO simulations remained elusive. An international team of researchers, spearheaded by Xiaojie Hao of the Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, has published groundbreaking findings revealing the key role of oceanic and atmospheric resolution in replicating the AMO’s true character.
This landmark study, published in Ocean-Land-Atmosphere Research on March 21, 2025, leverages the sophisticated Alfred Wegener Institute Climate Model (AWI-CM) to conduct a series of meticulously designed numerical experiments. By varying the spatial resolution of the ocean and atmosphere in four different configurations—low-resolution atmosphere with low-resolution ocean, high-resolution atmosphere with low-resolution ocean, low-resolution atmosphere with high-resolution ocean, and high-resolution atmosphere with high-resolution ocean—the team dissected how resolution influences the fidelity of simulated AMO cycles.
Intriguingly, their results demonstrate that increasing the resolution of ocean models is paramount to capturing the true temporal scale of AMO variability. Models utilizing low-resolution ocean grids produced spurious oscillations with repeat times of merely 10 to 20 years, inconsistent with observations. Contrastingly, high-resolution ocean simulations faithfully generated the classical 40 to 80-year periodicity intrinsic to the AMO, underscoring the ocean’s dynamical processes that only emerge when fine-scale currents and eddies are adequately resolved.
Beyond ocean resolution, enhancing atmospheric resolution contributed notably by refining the amplitude of the AMO in the simulations, aligning modeled temperature swings more closely with real-world measurements. This atmospheric detail improves the representation of transient weather phenomena that modulate oceanic conditions, such as blocking high-pressure systems and regional wind patterns, which in turn influence sea surface temperatures and ocean circulation.
The study’s true conceptual breakthrough lies in elucidating the feedback mechanisms linking the AMO to Fram Strait sea ice export (FSSIE) and atmospheric blocking over Greenland. Fram Strait is the gateway through which Arctic sea ice is transported from the polar region into the North Atlantic, impacting salinity gradients and ocean circulation—a critical driver of the Atlantic Meridional Overturning Circulation (AMOC). This circulation substantially modulates heat transport in the Atlantic, thereby influencing the AMO’s development and persistence.
By deploying the high-resolution ocean model, the researchers uncovered a positive feedback loop whereby the AMO phase regulates atmospheric blocking events over Greenland. During the warm AMO+ phase, reduced meridional temperature gradients encourage persistent atmospheric blocking, manifesting as high-pressure systems that suppress south-to-north winds. This inhibits Fram Strait sea ice export, maintaining high salinity in the Labrador Sea which supports a robust AMOC and prolongs the warm AMO phase. Conversely, in the cool AMO– phase, diminished blocking allows stronger winds to enhance sea ice export, lowering Labrador Sea salinity and weakening the AMOC, thus extending the cool phase.
This intricate dance between oceanic salinity, sea ice dynamics, and atmospheric circulation emerges as a pivotal mechanism through which the AMO sustains its multidecadal rhythm. Crucially, only models with sufficiently fine oceanic and atmospheric grids can replicate these interdependent phenomena, highlighting the indispensable role of multi-scale resolution in climate modeling.
Moreover, the enhanced atmospheric resolution accentuates processes such as transient weather events and detailed sea ice-atmosphere interactions. These refinements enable a more realistic simulation of how short-term atmospheric dynamics feed back into long-term ocean variability—bridging a gap between weather and climate scales that has historically challenged modelers.
The implications of these findings are profound for the future of climate prediction and risk assessment. Understanding and accurately simulating the AMO’s phases improves projections of extreme weather events, regional climate anomalies, and marine ecosystem shifts. It equips society with better-informed tools to anticipate and adapt to climate variability and change, particularly in vulnerable coastal communities and fisheries.
Looking ahead, Xiaojie Hao stresses the need for further investigations utilizing ultra-high-resolution models to unravel the full spectrum of physical mechanisms underlying low-frequency climate oscillations like the AMO. Such endeavors will refine our grasp of ocean-atmosphere interactions and the feedback loops shaping Earth’s climate system over decades and centuries.
Contributing to this study were distinguished collaborators including Dimitry V. Sein, Tobias Spiegl, Lu Niu, and Gerrit Lohmann from the Alfred Wegener Institute, alongside Xianyao Chen of the Ocean University of China and affiliated institutions in Russia and Germany. Their multidisciplinary expertise spanning physical oceanography, atmospheric sciences, and computational climate modeling underscores the collaborative nature required for breakthroughs in Earth system science.
This research was supported by several key funding bodies, including the Natural Science Foundation of China, the Germany-Sino Joint Project, the Fundamental Research Funds for the Central Universities, the MHESRF Scientific Task, and the Moscow Institute of Physics and Technology Development Program, reflecting the international commitment to resolving climate complexities.
Ultimately, this work marks a significant step forward in climate science by explicitly demonstrating that the resolution of oceanic and atmospheric components in numerical models is not merely a technical choice but a fundamental prerequisite for capturing the CANONICAL behavior of the Atlantic Multidecadal Oscillation. It opens a promising pathway toward more reliable climate forecasts and enhanced resilience to the profound environmental changes reshaping our planet.
Subject of Research: Not applicable
Article Title: Modeling the Atlantic Multidecadal Oscillation: The High-Resolution Ocean Brings the Timescale; the Atmosphere, the Amplitude
News Publication Date: 21-Mar-2025
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Image Credits: Figure from Modeling the Atlantic Multidecadal Oscillation: The High-Resolution Ocean Brings the Timescale; the Atmosphere, the Amplitude, created by Xiaojie Hao.
Keywords: Weather simulations, Climate modeling, Basic research, Discovery research, Earth systems science
