资源环境科技发展态势分析平台

The simulation of the northward-propagating monsoon intraseasonal oscillation (MISO) is still a grand challenge for climate models. Here, we show that the tilting of vorticity plays a critical role in the northward-propagating MISO. During the Indian summer monsoon (ISM), the persistent vertical easterly shear of background zonal wind sets up a horizontal vorticity. Due to the tilt of the meridional gradient of vertical velocity associated with convection, positive vorticity anomalies are generated to the north of the convection, where the convection is enhanced. In 19 coupled general circulation models from phase 6 of Coupled Model Intercomparison Project (CMIP6), it is confirmed that the simulations of MISO have a strong dependence on the simulations of this tilting but the tilting structures are not well captured in CMIP6 models. This offers a specific target for alleviating the model bias in MISO as well as in ISM in contemporary climate models.