Intraseasonal variability represents the dominant mode of variation in Indian summer monsoon precipitation, which is closely linked to the northward propagation of the Monsoon Intraseasonal Oscillation (MISO). Statistical analyses reveal that precipitation variance induced by the MISO accounts for over 60% of the total monsoon precipitation variance. State-of-the-art climate models generally underestimate monsoon precipitation intensity and produce biases in simulating the phase and amplitude of MISO northward propagation. The fundamental cause lies in their inability to accurately represent air-sea interaction mechanisms during MISO northward migration. Against this backdrop, this study utilizes datasets from 18 fully coupled ocean-atmosphere models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6). Composite analysis across multiple models indicates that inter-model differences in simulated MISO intensity are primarily attributed to biases in sea surface temperature (SST) magnitude, while the phase relationships of air-sea processes show no noticeable disparities among models. Warm SST anomalies and their meridional gradient anomalies to the north of the MISO can trigger stronger positive vorticity anomalies and latent heat flux anomalies, establishing favorable dynamical and thermodynamic conditions for convective development and MISO northward propagation. To further explore the origins of simulation biases, all models are classified into a well-simulated group and a poorly-simulated group based on their skills in reproducing intraseasonal precipitation. Comparative diagnostics demonstrate that the well-simulated group enhance low-level atmospheric convergence via the stretching effect of SST and its meridional gradient, thereby intensifying low-level vorticity to the north of the MISO. Additionally, these models present better coordination between warm SST anomalies and MISO-related surface winds, which effectively improves the simulation of latent heat flux. This study confirms that both momentum flux and heat flux serve as key oceanic feedbacks to atmospheric convection during MISO activities, and their simulation quality is directly dependent on the accuracy of SST and SST gradient simulations. The results provide important theoretical references for improving the simulation and prediction skills of the MISO and Indian summer monsoon precipitation.

暂无