The El Niño-Southern Oscillation (ENSO) system is the most significant equatorial interannual climate variability pattern and has enormous global climate impacts. The ability to forecast ENSO accurately is crucially important to human livelihoods worldwide. ENSO is characterized by strong winter-peaking sea surface temperature (SST) anomalies in the central-eastern tropical Pacific during the mature phase. However, the bias in simulating ENSO phase-locking behavior persists in climate models. In this study, the ENSO seasonal phase-locking behaviors simulated in 42 Coupled Model Intercomparison Project Phase 6 (CMIP6) models are evaluated by comparing 43 CMIP5 models and observations. Only a few models (12 CMIP5 and 15 CMIP6) simulated ENSO with a majority proportion of winter-peaking events, which indicates that reasonable ENSO seasonal phase-locking is still a challenge for state-of-the-art climate models. Furthermore, the seasonal cycle of the zonal SST gradient along the equator can explain approximately 24% and 27% of the variance in the ENSO phase-locking for CMIP5 and CMIP6, respectively. In particular, the strengths of the zonal SST gradient in the central-eastern Pacific during boreal spring and autumn are crucial. The biases in simulating the seasonal changes in the zonal SST gradient influence the zonal advective feedback's strengths that respond to the anomalous SST of ENSO, therefore disturbing the simulation of ENSO phase-locking. Improvement of the simulated ENSO phase-locking should be realized by focusing on the zonal SST gradient's seasonal cycle.

厄尔尼诺-南方涛动 (ENSO) 系统是最重要的赤道年际气候变率模式，对全球气候影响巨大。准确预测 ENSO 的能力对全世界人类的生计至关重要。ENSO 的特征是在成熟阶段中东部热带太平洋出现强烈的冬季峰值海面温度 (SST) 异常。然而，模拟ENSO锁相行为的偏差在气候模型中仍然存在。在本研究中，通过比较 43 个 CMIP5 模型和观测结果来评估在 42 个耦合模型比对项目第 6 阶段 (CMIP6) 模型中模拟的 ENSO 季节性锁相行为。只有少数模型（12 CMIP5 和 15 CMIP6）模拟了 ENSO 的大部分冬季峰值事件，这表明合理的 ENSO 季节性锁相对于最先进的气候模型仍然是一个挑战。此外，沿赤道的纬向海温梯度的季节性周期可以分别解释 CMIP5 和 CMIP6 的 ENSO 锁相方差的大约 24% 和 27%。特别是，北半球春季和秋季期间中东部太平洋的纬向海温梯度强度至关重要。模拟纬向海温梯度季节性变化的偏差会影响纬向平流反馈对ENSO异常海温响应的强度，从而干扰ENSO锁相的模拟。应通过关注纬向海温梯度的季节性周期来实现模拟 ENSO 锁相的改进。此外，沿赤道的纬向海温梯度的季节性周期可以分别解释 CMIP5 和 CMIP6 的 ENSO 锁相方差的大约 24% 和 27%。特别是，北半球春季和秋季期间中东部太平洋的纬向海温梯度强度至关重要。模拟纬向海温梯度季节性变化的偏差会影响纬向平流反馈对ENSO异常海温响应的强度，从而干扰ENSO锁相的模拟。应该通过关注纬向海温梯度的季节性周期来实现模拟ENSO锁相的改进。此外，沿赤道的纬向海温梯度的季节性周期可以分别解释 CMIP5 和 CMIP6 的 ENSO 锁相方差的大约 24% 和 27%。特别是，北半球春季和秋季期间中东部太平洋的纬向海温梯度强度至关重要。模拟纬向海温梯度季节性变化的偏差会影响纬向平流反馈对ENSO异常海温响应的强度，从而干扰ENSO锁相的模拟。应该通过关注纬向海温梯度的季节性周期来实现模拟ENSO锁相的改进。分别。特别是，北半球春季和秋季期间中东部太平洋的纬向 SST 梯度的强度至关重要。模拟纬向海温梯度季节性变化的偏差会影响纬向平流反馈对ENSO异常海温响应的强度，从而干扰ENSO锁相的模拟。应该通过关注纬向海温梯度的季节性周期来实现模拟ENSO锁相的改进。分别。特别是，北半球春季和秋季期间中东部太平洋的纬向海温梯度强度至关重要。模拟纬向海温梯度季节性变化的偏差会影响纬向平流反馈对ENSO异常海温响应的强度，从而干扰ENSO锁相的模拟。应该通过关注纬向海温梯度的季节性周期来实现模拟ENSO锁相的改进。因此干扰了ENSO锁相的模拟。应该通过关注纬向海温梯度的季节性周期来实现模拟ENSO锁相的改进。因此干扰了ENSO锁相的模拟。应该通过关注纬向海温梯度的季节性周期来实现模拟ENSO锁相的改进。