Progress of MJO Prediction at CMA from Phase I to Phase II of the Sub-Seasonal to Seasonal Prediction Project

Abstract

As one of the participants in the Subseasonal to Seasonal (S2S) Prediction Project, the China Meteorological Administration (CMA) has adopted several model versions to participate in the S2S Project. This study evaluates the models’ capability to simulate and predict the Madden-Julian Oscillation (MJO). Three versions of the Beijing Climate Center Climate System Model (BCC-CSM) are used to conduct historical simulations and re-forecast experiments (referred to as EXP1, EXP1-M, and EXP2, respectively). In simulating MJO characteristics, the newly-developed high-resolution BCC-CSM outperforms its predecessors. In terms of MJO prediction, the useful prediction skill of the MJO index is enhanced from 15 days in EXP1 to 22 days in EXP1-M, and further to 24 days in EXP2. Within the first forecast week, the better initial condition in EXP2 largely contributes to the enhancement of MJO prediction skill. However, during forecast weeks 2–3, EXP2 shows little advantage compared with EXP1-M because the increased skill at MJO initial phases 6–7 is largely offset by the degraded skill at MJO initial phases 2–3. Particularly at initial phases 2–3, EXP1-M skillfully captures the wind field and Kelvin-wave response to MJO convection, leading to the highest prediction skill of the MJO. Our results reveal that, during the participation of the CMA models in the S2S Project, both the improved model initialization and updated model physics played positive roles in improving MJO prediction. Future efforts should focus on improving the model physics to better simulate MJO convection over the Maritime Continent and further improve MJO prediction at long lead times.

摘 要

中国气象局(CMA)在参与国际次季节—季节(S2S)预测计划的第一到第二阶段,对S2S尺度重要现象—马登-朱利安振荡 (MJO)的预测能力逐步提升。本文利用中国气象局参加S2S计划的三个模式版本分别开展了历史模拟和回报试验(EXP1、EXP1-M和EXP2),进而探讨了模式对MJO预测的改进程度及可能原因。结果表明,在MJO 气候态模拟方面,新开发的高分辨率气候系统模式优于之前的中等分辨率模式。在MJO预测方面,由于初始条件的改进和模式的逐步更新,MJO的可用预测技巧从EXP1的15天提高到EXP1-M的22天,进一步在EXP2提高到24天。EXP2的MJO整体预测技巧最高,但其相比EXP1-M在预测第 2-3 周的改进并不明显。这主要是因为,针对第2-3初始位相的MJO预报,EXP1-M能够合理预测第2-3周的海洋大陆区域MJO对流异常和风场的响应关系,但EXP2对这种关系的预测能力快速下降。研究也同时指出,未来应侧重于进一步改进模式物理过程,尤其是海洋大陆区域MJO对流过程,从而提高MJO的预测技巧。