Seasonal prediction of South China April to May rainfall is examined based on forecasts by the European Centre for Medium-Range Weather Forecasts (ECMWF) operational model. El-Niño Southern Oscillation (ENSO) is a major source of predictability, conveyed by the lower tropospheric anomalous western Pacific anticyclone and cyclone for El-Niño and La-Niña respectively. By separating ENSO into its diversity of eastern Pacific (EP) and central Pacific (CP) ENSO, different effects on South China rainfall are revealed. From observations, while rainfall is enhanced following EP El-Niño and reduced following EP La-Niña, rainfall remains close to climatology following CP ENSO. However, the seasonal forecast model predicts CP ENSO effect on South China rainfall to be similar to EP ENSO. The model develops excessive westward extension of the eastern Pacific cold tongue within seasonal timescale. While model predicts tropical central Pacific anomalous sea surface temperature (SST) following CP ENSO realistically, the colder mean state is proposed to weaken the anomalous convection, which subsequently induces bias in the western Pacific anomalous rotational flow and hinders South China rainfall prediction. Meanwhile following EP ENSO, the colder mean state is proposed to strengthen the thermocline feedback, inducing stronger tropical eastern Pacific anomalous SST. While bias in the western Pacific anomalous rotational flow is also induced, the bias is far away from South China so rainfall prediction is still realistic. This study highlights the importance of model mean state in the fidelity of model ENSO diversity teleconnections on seasonal timescale.

根据欧洲中距离天气预报中心（ECMWF）的运行模型，对华南4月至5月的季节性降水进行了检查。厄尔尼诺南方涛动（ENSO）是可预测性的主要来源，对流层下部异常的西太平洋反气旋和旋风分别代表了厄尔尼诺和拉尼娜。通过将ENSO划分为东太平洋（EP）和中太平洋（CP）ENSO的多样性，揭示了对华南降水的不同影响。从观测结果看，虽然在EPEl-Niño之后降雨增加，而在EPLa-Niña之后降雨减少，但是CP ENSO之后的降雨仍然接近气候。然而，季节预报模型预测CP ENSO对华南降水的影响与EP ENSO相似。该模型在季节性时间尺度内使东太平洋冷舌向西过度扩展。虽然该模型实际上是根据CP ENSO预测热带中部太平洋异常海面温度（SST），但建议采用较冷的平均状态来减弱异常对流，这随后会引起西太平洋异常旋转流的偏差，并阻碍华南地区的降雨预报。同时，在EP ENSO之后，提出了较冷的平均态以增强温跃层的反馈，从而引起更强的热带东太平洋异常SST。虽然也引起了西太平洋异常旋转流的偏差，但该偏差远离华南，因此降雨预报仍然是现实的。