Out-of-phase decadal changes in boreal summer rainfall between Yellow-Huaihe River Valley and southern China around 2002/2003

摘要

This study investigates the decadal variability of rainfall over China in boreal summer (June-August) since the early 1990s. Results show that the rainfall experiences an abrupt decadal change at around 2002/2003. The decadal change is statistically significant and characterized by an out-of-phase pattern between southern China (SC) and the Yellow-Huaihe River Valley (YHRV). The rainfall over SC decreases during the decade 2003-2012 compared to that in the preceding decade 1993-2002. A simultaneous decadal increase in rainfall has occurred over the YHRV. Meanwhile, a significant sea surface temperature warming appears over the western Pacific Ocean and the northern Indian Ocean after 2002 on the decadal time scale. Further analysis reveals that enhanced convections are activated over the tropical regions between 130 degrees E and 160 degrees E and west of 80 degrees E due to the SST anomalies, which induce the dry air in an area of anomalous subsidence located over SC and the northern South China Sea (SCS) via zonal circulation. Accompanied by the anomalous descending flow over the northern SCS, tropical cyclone (TC) activities in the SCS also experience a concurrent decadal reduction. The decrease in landfall TCs contributes to the decadal decrease in SC rainfall since 2003. Corresponding to the anomalous descending motion that is dominant south of 30 degrees N, an anomalous moist ascending flow develops over the YHRV at around 35 degrees N. Meanwhile, the western Pacific subtropical high becomes stronger and extends further westward during 2003-2012, leading to enhanced moisture transport by the southwesterly in the northwestern flank of subtropical high. As a result, more precipitation occurs over the YHRV. The above analysis has revealed the physical-dynamical processes involved in the decadal changes in rainfall over China. The mechanisms behind the out-of-phase pattern of rainfall changes between SC and the YHRV that occurred at 2002/2003 are explored.