中国科学院大气物理研究所Fei ZHENG和Jiangbo JIN的团队近日取得一项新成果。经过不懈努力，他们揭示了CAS-ESM2模型所反映的热带西太平洋海温偏差引起的双ITCZ的来源。相关论文发表在2024年4月11日出版的《中国科学：地球科学》杂志上。

据研究人员介绍，“双ITCZ”是当前气候模式和地球系统模式中热带太平洋上空常见的降水偏差，但其形成原因仍值得探索和讨论。

本研究使用中国科学院第二版地球系统模型(CAS-ESM2)，通过对比一组热带太平洋海温(SST)偏差校正实验，从耦合模式的气候年平均偏差角度探讨海温偏差诱发“双ITCZ”的可能机制。结果表明，模拟的热带太平洋气候年平均海温偏差可以通过饱和比湿影响潜热通量的偏差，潜热通量的偏差可以通过凝结释放机制进一步影响湿空气垂直速度，最终调节降水的模拟偏差。

此外，通过不同试验的对比发现，双ITCZ的存在可能主要来自热带西太平洋的年平均海温偏差，本研究通过提出的“海温—饱和比湿—潜热通量—垂直速度—降水”的海气耦合过程，为减少热带太平洋模式中的耦合偏差以提高CAS-ESM2气候模拟精度提供了可能的途径。

附：英文原文

Title: The source of Double ITCZ induced by the SST bias over the tropical western Pacific as reflected in CAS-ESM2 Model

Author: Jinning TONG, Fei ZHENG, Jiangbo JIN, Ruowen YANG, Jiang ZHU, Qingcun ZENG

Issue&Volume: 2024/04/11

Abstract: “Double ITCZ” is a common precipitation bias over the tropical Pacific in current climate models and Earth system models, but the reasons for its formation are still worth exploring and discussing. In this study, we adopted the second version of Chinese Academy of Sciences Earth System Model (CAS-ESM2), by comparing a set of sea surface temperature (SST) bias correction experiments over the tropical Pacific, to explore the possible mechanism of SST bias on inducing the “Double ITCZ” from the perspective of the climatic annual mean bias in the coupled model. We revealed that the simulated climatic annual mean SST bias over the tropical Pacific can affect the bias of latent heat flux through the saturation specific humidity, and the bias of latent heat flux can further affect that of vertical velocity of humid air by the condensation release mechanism, and finally modulate the simulated bias in precipitation. Furthermore, through the inter-comparison between different experiments, it is found that the source of Double ITCZ might mainly come from the annual mean SST bias over the tropical western Pacific through the proposed air-sea coupled process of “SST-saturated specific humidity-latent heat flux-vertical velocity-precipitation”, indicating a possible way on reducing the couple biases in models over the tropical Pacific to improve the accuracy of CAS-ESM2 for climate simulation.

DOI: 10.1007/s11430-023-1304-5

Source: https://www.sciengine.com/10.1007/s11430-023-1304-5