Influence of the Northwest Pacific tripole mode on the mid-summer precipitation in North China and the regulation by the North Atlantic

The North China mid-summer (July) precipitation (NCJP) contributes the largest proportion of total annual precipitation in North China, with significant interdecadal and interannual variability. The interannual variability of the NCJP was further investigated on the basis of a study of its interdecadal variability and found that a sea surface temperature (SST) pattern in July located in the northwest Pacific, defined here as the northwest Pacific SST tripole (NWPT), can significantly influence the interannual variability of the NCJP, and that this relationship is regulated by the decadal northern North Atlantic SST (NNASST). Diagnostic analysis and the linear baroclinic model experiment indicate that the positive (negative) NWPT in July can excite an anomalous anticyclone (cyclone) in the region centered on the Korean peninsula and an anomalous cyclone (anticyclone) in the northwest Pacific off southeast Japan, thereby strengthening (weakening) the NCJP. When the decadal NNASST is in a significantly positive phase, the positive geopotential height anomalies it excites in the northwestern region off North China are not favorable for the connection between the NWPT and the NCJP. When the decadal NNASST is in a negative or insignificantly positive phase, the July NWPT and the NCJP have a significant positive correlation on interannual timescale.