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Most state-of-art models project a reduced equatorial Pacific east-west temperature gradient and a weakened Walker circulation under global warming. However, the causes of this robust projection remain elusive. Here, we devise a series of slab ocean model experiments to diagnostically decompose the global warming response into the contributions from the direct carbon dioxide (CO2) forcing, sea ice changes, and regional ocean heat uptake. The CO2forcing dominates the Walker circulation slowdown through enhancing the tropical tropospheric stability. Antarctic sea ice changes and local ocean heat release are the dominant drivers for reduced zonal temperature gradient over the equatorial Pacific, while the Southern Ocean heat uptake opposes this change. Corroborating our model experiments, multimodel analysis shows that the models with greater Southern Ocean heat uptake exhibit less reduction in the temperature gradient and less weakening of the Walker circulation. Therefore, constraining the tropical Pacific projection requires a better insight into Southern Ocean processes.
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This content will become publicly available on October 1, 2026
Ocean Circulation Change Modulates Tropical Atmospheric Circulation in a Warming Climate: The Role of Ocean Heat Uptake
Abstract Deep convection associated with large-scale tropical atmospheric circulations governs tropical precipitation. Under anthropogenic warming, the weakened Walker and Hadley circulations alter tropical rainfall. Ocean circulations are also expected to change due to global warming, impacting tropical atmospheric circulation systems. From the perspective of ocean heat uptake, we investigate how ocean circulation change modulates tropical atmospheric circulation and vertical motion under CO2warming by comparing fully coupled and slab-ocean simulations. We find that the slowed South Equatorial Current and subtropical cells in the Pacific induce anomalous advective warming, reducing ocean heat uptake in the central-western tropical Pacific. This, combined with increased downward radiation at the top of atmosphere and horizontal moisture advection, escalates the moisture static energy in the air column and promotes ascent in this region, shifting the Pacific Walker circulation eastward and strengthening the Pacific Hadley circulation. Across the tropical Indian Ocean, ocean heat uptake shows a dipole-like change, increasing in the eastern Indian Ocean and seas surrounding marine continents while decreasing in the western Indian Ocean. The former ocean heat uptake increase is triggered by anomalous oceanic vertical advective cooling, which abates the moisture static energy in the air column and inhibits the ascent in the area. The latter ocean heat uptake decrease is prompted by anomalous oceanic advective warming from both horizontal and vertical directions, which enhances the moisture static energy in the air column, resulting in anomalous upward motions. Over most of the tropics, ocean dynamics help attenuate the strengthening of the gross moist stability due to CO2increase, thereby promoting ascent or weakening descent in the atmosphere. Significance StatementLarge-scale tropical atmospheric circulations are expected to weaken as a result of global warming, having a significant impact on tropical precipitation. Because the atmosphere and oceans are inextricably linked, any subtle change in one can affect the other. For this reason, it is critical to understand the role of ocean circulation change in steering the response of large-scale tropical atmospheric circulation to anthropogenic warming. This study approaches the aforementioned scientific question from the novel perspective of ocean heat uptake. It demonstrates how changes in ocean circulation affect heat uptake over tropical oceans, modifying vertical motion and the Walker and Hadley cells in the tropical atmosphere in a warming climate.
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- PAR ID:
- 10643618
- Publisher / Repository:
- AMS
- Date Published:
- Journal Name:
- Journal of Climate
- Volume:
- 38
- Issue:
- 19
- ISSN:
- 0894-8755
- Page Range / eLocation ID:
- 5305 to 5321
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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