1. Processes Driving the Intermodel Spread of the Southern Hemisphere Hadley Circulation Expansion in CMIP6 Models.
- Author
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Hur, Ije, Yoo, Changhyun, Yeh, Sang‐Wook, Kim, Young‐Ha, and Seo, Kyong‐Hwan
- Subjects
BAROCLINICITY ,JET streams ,STREAM function ,EDDY flux ,ORTHOGONAL functions - Abstract
The Hadley circulation (HC) has been expanding poleward in recent decades. The Coupled Model Intercomparison Project Phase 6 (CMIP6) models predict that the expansion will accelerate in the future, more so in the Southern Hemisphere (SH). However, the extent of the expansion varies widely among the models. We investigate the mechanisms driving the intermodel spread in SH HC expansion predictions. The intermodel spread is obtained by an empirical orthogonal function analysis on the SH HC trend patterns of 16 CMIP6 model simulations using the historical and shared socioeconomic pathway 5–8.5 scenarios. The leading mode, showing a mean meridional stream function anomaly at the poleward SH HC extent, explains 49.73% of the variance and significantly correlates (r = 0.94) with the SH HC expansion. By analyzing the extended Kuo‐Eliassen equation, we find that the intermodel difference in the representation of diabatic heating is responsible for about 14% of the intermodel spread. The meridional eddy momentum and heat fluxes contribute to about 21% and 18% of the intermodel spread, respectively. The models simulating a relatively large SH HC expansion tend to show increased precipitation in the Southern Pacific Convergence Zone, reduced baroclinic instability in the subtropics, and an enhanced poleward shift of jet stream in the midlatitudes. This suggests that the uncertainty in the HC projection may be constrained by reducing the bias in the trend of the mean fields. Plain Language Summary: The Hadley circulation (HC), which affects global climate patterns, is expanding toward the poles. However, different climate models predict varying extents of this expansion, especially in the Southern Hemisphere (SH). We aim to understand why. By analyzing climate model data, we identified key factors influencing the spread in SH HC expansion. Our findings suggest that factors like diabatic heating and meridional eddy momentum play significant roles. Models showing greater SH HC expansion tend to simulate increased precipitation in specific regions and shifts in atmospheric jet streams. Addressing these model biases could help reduce uncertainty in future HC projections. Key Points: The first intermodel stream function trend mode effectively captures the spread of the Southern Hemisphere Hadley Circulation expansionThe intermodel spread in expansion is explained by the spread of the meridional eddy momentum, heat fluxes, and diabatic heatingThe spread of the eddy fluxes and diabatic heating are linked with the changes in precipitation, jet, and static stability [ABSTRACT FROM AUTHOR]
- Published
- 2024
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