Preliminary analysis of the zonal distribution of ENSO-related SSTA in three CMIP5 coupled models

ABSTRACT

The simulated sea surface temperature anomaly (SSTA) over the tropical Pacific during El Niño–Southern Oscillation (ENSO) is investigated in three representative coupled models: CESM1-CAM5, FGOALS-s2, and FGOALS-g2. It is found that there is a significant westward shift bias in reproducing the zonal distribution (ZD) of the ENSO-related SSTA in CESM1-CAM5 and FGOALS-s2, whereas the SSTA-ZD simulated by FGOALS-g2 is relatively realistic. Through examining the SSTA-ZD during both warm and cold phases of ENSO separately, the authors reveal that the SSTA-ZD simulation bias during the ENSO cycle mainly lies in the bias during the warm phase. It is noted that both the simulated zonal wind stress anomaly (${\tau }_x^{\prime }$) and shortwave heat flux (SW) anomaly exhibit westward shift biases in CESM1-CAM5 and FGOALS-s2, while the counterparts in FGOALS-g2 are relatively reasonable. The westward shift biases in representing ${\tau }_x^{\prime }$ and the SW anomaly (SWA) are attributed to the westward-shifted precipitation anomaly (PrA). It is suggested that the mean SST cold bias over the cold tongue region is the key factor behind the westward-shift bias in simulating the El Niño-related PrA, which leads to the westward-shifted ${\tau }_x^{\prime }$ and SWA. Collectively, the aforementioned anomaly fields, including the dynamic part (${\tau }_x^{\prime }$) and thermodynamic part (SWA), contribute to the westward-shift bias in simulating the El Niño-related SSTA. This study provides clues for understanding the ZD simulation biases of ENSO-related fields; however, further in-depth investigation with more model simulations, especially the incoming CMIP6 simulations, is still needed to fully understand the ENSO SSTA-ZD simulation bias in coupled models.

Graphical abstract

摘要

本文分析了三个典型的 CMIP5 耦合模式 (CESM1-CAM5, FGOALS-s2 和 FGOALS-g2) 中 ENSO 海温异常纬向空间分布的模拟偏差, 并对偏差成因做了初步分析。发现三个耦合模式中 ENSO 海温异常纬向分布都表现出不同程度地偏西, 进一步分解发现这一模拟偏差主要来源于 ENSO 正位相, 即, 耦合模式中模拟的厄尔尼诺事件暖海温异常较观测具有明显的偏西偏差。对厄尔尼诺事件进一步合成分析表明, 海温异常纬向空间分布的模拟偏差主要与大气中的纬向风应力异常纬向分布偏西的偏差以及短波辐射异常的强度模拟偏差紧密相关, 该偏差是由厄尔尼诺期间降水异常响应模拟偏西导致的, 而降水异常的模拟偏差则源于赤道冷舌区冷舌过冷。值得指出的是, 该工作只初步探讨了气候背景场中平均海温冷偏差的影响, 并未讨论气候背景场中其他部分的影响, 且只基于有限的三个模式, 主要集中分析了与海温异常纬向分布紧密相关的大气过程的影响, 并未涉及相关的海洋过程的模拟偏差是否起作用, 因此, 将来有必要基于多模式数据集对 ENSO 海温异常纬向分布偏差做更深入的定量诊断和分析。

KEYWORDS:

• ENSO
• SSTA zonal distribution
• coupled models
• simulation bias

关键词:

• ENSO
• 海温异常纬向分布
• 耦合模式
• 模拟偏差

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was jointly supported by the National Key Research and Development Program of China [Grant No. 2019YFC1510004], Natural Science Foundation of Jiangsu Province [Grant No. BK20190781], the General Program of Natural Science Foundation of Jiangsu Higher Education Institutions [Grant No. 19KJB170019], the open fund of State Key Laboratory of Loess and Quaternary Geology [Grant No. SKLLQG1802], and the LASG Open Project.