Reduced ITCZ meridional asymmetry under global warming in CMIP6 models

Le résumé fourni par la source

The annual-mean Intertropical Convergence Zone (ITCZ) locates in the northern tropics and exhibits a pronounced hemispheric asymmetry. Many studies have explained this interhemispheric asymmetry from the perspective of both global energy transport and tropical air–sea coupling processes. However, how this meridional asymmetry responds to global warming remains unclear. Using the outputs of CMIP6 models, this study investigates potential changes in the ITCZ’s meridional asymmetry under the high-emission SSP5-8.5 scenario compared to the historical runs. A robust reduction in the ITCZ’s meridional asymmetry is found in the warming climate, characterized by enhanced precipitation in the southern tropics. This change can be explained from the perspective of global energy transport. The weakening Atlantic Meridional Overturning Circulation under global warming reduces northward cross-equatorial oceanic heat transport, requiring less compensatory southward atmospheric energy transport and thus favoring a more symmetric ITCZ. Further, from the local air–sea coupling perspective, an El Niño-like warming pattern in the eastern tropical Pacific enhances the local air–sea coupling and causes more precipitation, especially in the southern-central tropical Pacific and coastal oceans off Peru, reducing the hemispheric asymmetry of ITCZ. 年平均热带辐合带 (ITCZ) 位于北半球热带地区, 表现出明显的半球不对称性.许多研究从全球能量输送和热带海气耦合过程的角度解释了这种半球间的不对称性.然而, 这种经向不对称如何应对全球变暖尚不清楚.本研究利用CMIP6模型的输出, 与历史运行相比, 研究了高排放SSP5-8.5情景下ITCZ经向不对称性的可能变化.在气候变暖的情况下, ITCZ的经向不对称性显著降低, 其特征是南半球热带地区降水增加.这种变化可以从全球能量输送的角度来解释.全球变暖下, 减弱的大西洋经向翻转环流减少了向北的跨赤道海洋热输送, 需要较少的向南大气能量的补偿输送, 从而产生了更对称的ITCZ.此外, 从局地海气耦合的角度来看, 热带太平洋东部类似厄尔尼诺的变暖模式增强了局地的海气耦合, 并导致更多的降水, 特别是在热带太平洋中南部和秘鲁附近的沿海海洋, 最终减少了ITCZ的半球不对称性.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.