An interdecadal enhancement of relationship between Northwest and North China summer precipitation since early 2000.

The present study investigates a significant enhancement in the relationship between summer precipitation in Northwest China (NWC) and that in North China (NC) (the NWC and NC region) after early 2000, using the CN05.1 dataset and the NCEP-NCAR reanalysis circulation data from 1961 to 2018. The change in the relation between summer precipitation variations in these two regions after early 2000 likely relates to the change of the wave trains in mid-high latitudes. Before 2000, atmospheric circulation anomalies associated with the summer precipitation in NWC resemble the Silk Road Pattern (SRP) and the British-Baikal Corridor (BBC) pattern, but that in NC only resembles the SRP. After 2000, the summer precipitation in NWC and NC has a significant positive correlation with the BBC pattern. The BBC pattern influences summer precipitation in NWC and NC after early 2000 through the Ural blocking high, the positive 500-hPa Z anomalies over the Mediterranean Sea and Northwest Pacific, and the East Asia trough that leads the cold air to the south. These four synoptic systems co-modulate the summer precipitation in NWC and NC. In addition, when NWC has the same (opposite) sign as NC summer precipitation, there is BBC (SRP) wave train across Eurasia at high (middle) latitudes. [ABSTRACT FROM AUTHOR]