Possible impacts of the interannual variability of the Australian high on summertime rainfall in China as revealed by the SVD analysis.

The Australian high as an important circulation member of the East Asian summer monsoon system has significant impacts on the summertime climate of China. By using the sea level pressure data from the NCEP/NCAR reanalysis data and the monthly mean data of rainfall at 107 stations in China， the relationships between the interannual variability of the Australian high and summer precipitation in China have been studied with the singular value decomposition (SVD) and regression methods. The time series of the coefficient for the first mode of the singular vector (SVD1) is found to be very highly correlated with the Australian high index (correlation:0.98), in agreement with the results in many other studies, showing that the SVD1 is able to well depict the variations of the Australian high. The first mode displays the close relationship between the interannual variability of Australian high and summer precipitation in the regions south of the Yangtze River. When the Australian high is stronger (weaker) than normal， summer precipitation in regions south of the Yangtze River will be significantly more (less) than normal. The Australia high influences summer precipitation in China via changing both the zonal and the crossequatorial flows in the equatorial region and via a way like the wave train P-J. When the Australian high is stronger than normal, the location of the west Pacific subtropical high seems to be more southern and western than normal， inducing the intensification of the cross equatorial flow at 105°E, which transports ample water vapor northeastward to the regions south of the Yangtze River and thus enhances rainfall there. When the Australian high is weaker than normal, the scenario is opposite. Negative SSTA in the regions around Indonesia and intertropical convergence zone during strong (weak) Australia high pressure years will cause anomalous divergence (convergence) in the lower troposphere, including the anomalous anticyclonic (cyclonic) circulation in both the southern Australia and the northwest Pacific. Simultaneously, the anomalous convergence (divergence) is also induced in the regions south of the Yangtze River, resulting in the anomalous ascent (decent) of air, which eventually facilitates more (less) rainfall in the regions south of China in boreal summer.