ABSTRACT

It was found in previous observational studies that the quasi-biennial oscillation (QBO) can modulate the teleconnection over the Atlantic basin related to the Madden–Julian Oscillation (MJO). In this study, we assess the modulation of the MJO-related teleconnection by the QBO in the operational models that participated in the subseasonal-to-seasonal prediction (S2S) project of the World Climate Research Programme/World Weather Research Programme. The enhancement of the positive North Atlantic Oscillation (NAO) after the occurrence of MJO phase 3, which corresponds to enhanced convection in the equatorial Indian Ocean and reduced convection in the tropical western Pacific, under westerly QBO (WQBO) conditions is seen to be captured by most S2S models but, not unexpectedly, to different degrees. In contrast, the enhancement of the NAO after the occurrence of MJO phase 7, when tropical convection anomalies have the opposite signs compared with MJO phase 3, under WQBO conditions is not reproduced in most S2S models. Under easterly QBO (EQBO) conditions, however, some S2S models can reproduce a significant negative NAO after the occurrence of MJO phase 7 but not a positive NAO after the occurrence of MJO phase 3. The results indicate that although the S2S models are able to predict a reasonable MJO up to around three weeks, representing the impact of the QBO on the extratropical teleconnection of the MJO remains challenging.

摘要

在之前的观测研究中发现，准双年振荡 (QBO) 可以调节与马登-朱利安振荡 (MJO) 相关的大西洋海盆上的遥相关。在这项研究中，我们评估了 QBO 在参与世界气候研究计划/世界天气研究计划的次季节到季节预测 (S2S) 项目的业务模型中对 MJO 相关遥相关的调制。在 MJO 阶段 3 发生后正北大西洋涛动 (NAO) 的增强，这对应于赤道印度洋的对流增强和热带西太平洋的对流减少，在西风 QBO (WQBO) 条件下被捕获大多数 S2S 模型，但不出所料，程度不同。相比之下，在 MJO 阶段 7 发生后 NAO 的增强，当热带对流异常与 MJO 阶段 3 相比具有相反的符号时，在 WQBO 条件下，大多数 S2S 模型没有重现。然而，在东风 QBO (EQBO) 条件下，一些 S2S 模型可以在 MJO 阶段 7 发生后重现显着的负 NAO，但在 MJO 阶段 3 发生后不能重现显着的 NAO。结果表明，虽然 S2S 模型能够预测合理的 MJO 长达三周左右，代表 QBO 对 MJO 温带遥相关的影响仍然具有挑战性。