Differences in monthly evolution of the western Pacific subtropical high (WPSH) in summer for different modes of intraseasonal variation of the summer monsoon rain belt (IVSMRB) are examined by using the composition method. For such analysis, the rainfall data from 160 stations in China, 850 hPa wind derived from the National Centers for Environmental Prediction and the National Center for Atmospheric Research (NCEP/NCAR) reanalysis dataset, and the National Oceanic and Atmospheric Administration (NOAA) extended reconstructed sea surface temperature (SST), are used. In addition, the characteristics of the pre-winter East Asia monsoon, Pacific sea surface temperature anomalies (SSTA), and rain styles in summer relative to these modes are investigated by using composition and correlation methods.Results show that the twice northward jumps of WPSH from spring to summer differ significantly among the modes, and that for each mode is relatively independent. The first jump of WPSH has an important influence on rain belt distribution in June, while the second jump has decisive influence on that in July and August.
The influence of SSTA in the Pacific on IVSMRB in China is multi-modal. In different phases of the Monsoon/El Niño-Southern Oscillation (ENSO) cycle, the IVSMRB presents dissimilar features. The first mode appears mainly in the decay phase of El Niño, and the second generally appears in the developing phase of La Niña. The third occurs in the developing phase of El Niño;the fourth, in the decay phase of La Niña;the fifth, at weak ENSO signals;and the sixth, in the persisting phase of La Niña. Moreover, the SSTA in different key regions has different impact on the IVSMRB. The SSTA in Kuroshio has a strong correlation with the rain belt variation in June, while the ENSO cycle in eastern tropical Pacific has an important influence on the rain belt variation in July and August. Analysis of the relationship between the IVSMRB modes and summer rain styles reveals some linkage between the two;however, these results do not imply that they can be substituted for each other.