Excitation Mechanisms of the Teleconnection Patterns Affecting the July Precipitation in Northwest China

Using observational rainfall data and atmospheric reanalysis data, the precipitation variations in Northwest China during July and the corresponding atmospheric teleconnection patterns are studied. The results indicate that the leading modes of July precipitation variations in Northwest China are affected by the Silk Road pattern and the Europe-China (EC) pattern. The analysis suggests that the circumglobal teleconnection (CGT) could be considered as the interannual component of the Silk Road pattern. To investigate the excitation mechanisms for the CGT pattern and EC pattern on interannual time scales, the singular value decomposition (SVD) analysis is performed between 200-hPa meridional wind velocity over the region of (30 degrees-60 degrees N, 30 degrees-130 degrees E) and tropical rainfall between (15 degrees S and 30 degrees N). The results suggest that the tropical heating anomalies most responsible for the CGT pattern are located over the North Indian Ocean, and the tropical heating anomalies most responsible for EC pattern are located over equatorial central Pacific, Indonesia, and tropical Atlantic. The tropical heating anomalies excite the CGT pattern and EC pattern by inducing divergent flow at the upper troposphere, and the advections of vorticity by the divergent component of the flow act as effective Rossby wave sources. Further analysis indicates that the tropical rainfall anomalies responsible for the CGT pattern and EC pattern are the leading modes of tropical rainfall variations, and these modes of tropical rainfall variations are related to the SST anomalies.