Climate Model Biases in Tropical Ocean Dynamics

Climate models systematically misrepresent the mean state and variability of the tropical oceans, giving rise to pronounced sea surface temperature (SST) and precipitation biases. A persistent warm equatorial SST bias and the double intertropical convergence zone (ITCZ) precipitation bias are underpinned by errors in wind stress, convective parameterisations, cloud radiative forcing and ocean–atmosphere feedbacks. Excessive shortwave radiation and cloud misrepresentation drive warm SST biases in eastern boundary upwelling regions such as the southeastern tropical Atlantic and Pacific cold tongue, distorting monsoon onset, tropical cyclone genesis and remote rainfall patterns across adjacent continents. Equatorial wind stress errors further amplify SST biases by weakening coastal upwelling and enhancing mixed‐layer stratification, while barrier layers modulate surface cooling through salinity effects. Although increases in atmospheric and oceanic resolution have yielded partial improvements—particularly in reducing warm SST and cloud biases—many errors persist, indicating the need for refined physics schemes. The reduction of these biases is essential for improving projections of tropical variability, monsoon dynamics and global climate teleconnections.

Research from Nature Portfolio

Recent studies have demonstrated that enhanced atmospheric resolution is essential to simulate the seasonal evolution of the Atlantic cold tongue and its coupling to the West African Monsoon. By employing a high‐resolution atmospheric component, models achieve a more realistic inland migration of the precipitation maximum and a more accurate seasonal phase‐locking of equatorial sea surface temperature variability. This improved representation of cold tongue development leads to a better timing and strength of Sahel rainfall onset, highlighting the critical role of equatorial ocean dynamics in modulating regional monsoon systems.

Climate Model Biases in Tropical Ocean Dynamics publication trend

The graph below shows the total number of articles in climate model biases in tropical ocean dynamics across all publications each year (not limited to Nature Index journals).

Technical terms

Sea surface temperature bias: The systematic difference between simulated and observed SST that affects ocean–atmosphere exchanges.

Intertropical convergence zone (ITCZ): A belt of low‐pressure and convective activity near the equator that governs tropical precipitation patterns.

Cold tongue: A region of relatively low SST along the equator caused by upwelling of colder subsurface waters.

Wind stress: The force exerted by surface winds on the ocean surface, driving currents and upwelling.

Barrier layer: A layer of water with distinct salinity stratification that inhibits vertical mixing of the mixed layer.

Convective parameterisation: A numerical scheme in climate models to represent the effects of unresolved convective processes on heat and moisture transport.

References

1. The link between intertropical convergence zone stagnation and bias in local shortwave cloud radiative forcing over tropical Africa in climate models. Environmental Research Letters (2023).
2. Improvements and persistent biases in the southeast tropical Atlantic in CMIP models. npj Climate and Atmospheric Science (2022).
3. Role of wind stress in driving SST biases in the Tropical Atlantic. Climate Dynamics (2019).
4. Barrier layers and tropical Atlantic SST biases in coupled GCMs. Tellus A Dynamic Meteorology and Oceanography (2008).
5. Convective Boundary Layer Control of the Sea Surface Temperature in the Tropics. Journal of Advances in Modeling Earth Systems (2020).
6. Impact of increased resolution on long-standing biases in HighResMIP-PRIMAVERA climate models. Geoscientific Model Development (2022).
7. Sahel rainfall strength and onset improvements due to more realistic Atlantic cold tongue development in a climate model. Scientific Reports (2018).
8. Impact of tropical Atlantic sea-surface temperature biases on the simulated atmospheric circulation and precipitation over the Atlantic region: An ECHAM6 model study. Climate Dynamics (2016).