Meiyu is a critical component of the summer rainy season over the Yangtze–Huaihe River Basin (YHRB) in China, and the Meiyu onset date (MOD), serving as a key indicator of Meiyu, has garnered substantial attention. This article demonstrates an in-phase relationship between MOD and the preceding spring Barents–Kara Seas ice concentration (BKSIC) during 1979–2023. Specifically, the loss of spring BKSIC promotes an earlier MOD. Further analysis indicates that decreased spring BKSIC reduces the reflection of shortwave radiation, thereby enhancing oceanic solar radiation absorption and warming sea surface temperature (SST) in spring. The warming SST persists into summer and induces significant deep warming in the BKS through enhanced upward longwave radiation. The BKS deep warming triggers a wave train propagating southeastward to the East Asia–Northwest Pacific region, leading to a strengthened East Asian Subtropical Jet and an intensified Western North Pacific Subtropical High in summer. Under these conditions, the transport of warm and humid airflows into the YHRB is enhanced, promoting convective instability through increased low-level warming and humidity, combined with enhanced wind shear, which jointly contribute to an earlier MOD. These results may advance the understanding of MOD variability and provide valuable information for disaster prevention and mitigation.

The anomalous zonal wind moves southward during the ENSO mature phase in boreal winter. Previous studies suggest that it may be caused by the nonlinear interaction of annual cycles or the influence of background mean state changes. In this research, the ECHAM4.6 atmospheric model is used to confirm the mechanism of the anomalous zonal wind southward shifting. The annual cycle of solar radiation and SST are removed in the sensitivity experiments to avoid the interaction between the ENSO and annual cycle. The results show that the north–south asymmetry mode of the ENSO anomalous wind field is not the result of a nonlinear interaction between ENSO and the annual cycle. The mean v-winds in winter motivate the southward shifting of the ENSO anomalous wind field through advection.

The impact of the mean state on simulated western North Pacific anomalous anticyclone (WNPAC) during El Niño mature winter was studied through the diagnosis of 45 historical climate experiments from the CMIP6. The result indicates that in addition to the model-simulated El Niño-related sea surface temperature anomalies (SSTA), the atmospheric mean state also plays an important role in modulating the intermodel spread of WNPAC, especially the intensity and zonal location. On one hand, the central Pacific mean-state precipitation/moisture fields can modulate the western North Pacific (WNP) thermal condition responded to the SST forcing in the Niño-3.4 region through a local circulation-convective feedback, and thus affecting the intensity of WNPAC. On the other hand, the mean-state meridional vorticity gradient in the WNP and the westward-extended central Pacific warming may have acted together to regulate the WNPAC zonal location.