Decadal transition of moisture sources and transport in northwestern China during summer from 1982 to 2010

Abstract

The northwestern corner of China (NWCC) experienced a decadal transition in summer precipitation during 1982–2010, with a significant upward trend in 1982–2000 (P1) but a downward one in 2001–2010 (P2). A spatially unbounded dynamic recycling model is developed to estimate the moisture sources and moisture transport variations based on ERA-Interim data. The results suggest that more than 88% of NWCC precipitation has external moisture origins in the southwest and northwest terrestrial areas. The increasing precipitation trend during P1 can be explained by the increasing moisture contribution from the southwest and decreasing contribution from the northwest. However, the opposite trends cause the decreasing precipitation trend during P2. In general, the decadal precipitation transition is mainly determined by the variation of short-distance moisture transport from central Asia, although opposite moisture transport variations exist in the Ural Mountains and Northeast Europe. The variation of the precipitation trend is closely associated with a well-organized wave train propagation from the North Atlantic to central Asia. During P1, the wave train structure consists of a titled positive phase North Atlantic Oscillation (NAO), an anticyclonic circulation over Europe, and a cyclonic anomaly over central Asia, which promotes the southwest moisture flux to NWCC. But the opposite circulation pattern dominates P2. The energy dispersion due to the breakdown of the NAO determines the phase and strength of the downstream wave anomalies over Eurasia. This suggests that the summer NAO might influence the decadal variation of NWCC precipitation through the decadal modulation of the Eurasia wave train.