Remote Impact of the QBO-MJO on early summer precipitation in Eastern Asia: model evidence from CMIP6

The Quasi-biennial Oscillation (QBO) influences the response of Eastern Asian precipitation in early summer to tropical Madden–Julian Oscillation (MJO). This study first assesses the reproducibility of models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) in capturing the early summer rainfall signals in Eastern Asia associated with the QBO and MJO, complementing their widely reported impact on winter precipitation. Models with an internally generated QBO simulate qualitatively different QBO or MJO teleconnections, and high-skill and low-skill models are compared to better comprehend the mechanism of the linkage between QBO-MJO combinations and Eastern Asian rainfall. The evaluation shows that most models underestimate the average strength of the MJO, while a few individual models overestimate it. Other biases also include the too-weak peak amplitude, spatial shift in the anomalous convection center, tilting of the active convection band, and errors in the relative contribution of the two multivariate leading modes. It is still difficult for most models to catch all aspects of the MJO convection in early summer. As a consequence, only a few models capture the possible QBO’s modulation of the MJO and the potential influence of the QBO-MJO combination on Eastern Asian precipitation in early summer. The models that successfully simulate the anomalous convection related to the QBO and MJO also represent better teleconnections to the early summer rainfall in Eastern Asia, which provide further modeling evidence that the QBO-MJO combination adds subseasonal predictability of the early summer rainfall in Eastern Asia.