What Controls the Interdecadal Enhancement in Interannual Variability of Summertime Intraseasonal Precipitation Over South China?

This study focuses on the interannual variability of summertime intraseasonal precipitation intensity (SIPI) over South China (SC) in the 30-90-day range. The results demonstrate a significant increase in the interannual variability of SIPI over SC around the mid-1990s. By comparing atmospheric and oceanic anomalies between two periods, P1 (1984-1993) and P2 (1994-2003), we identify that both the Silk Road pattern (SRP) and the western Pacific subtropical high (WPSH) play a role in influencing this interdecadal increase in SIPI interannual variability. These system anomalies are modulated by sea surface temperature anomalies (SSTA) in the North Atlantic (NA) and equatorial East Pacific (EP). During years with positive precipitation anomalies in P2, warming EP SSTA induces anomalous Walker cell and local Hadley cell, weakening the WPSH and enhancing convective activity, and increasing moisture transport over SC. The warming NA SSTA near 45 degrees N triggers a more southerly propagation of SRP, thereby providing additional disturbance energy that enhances summer precipitation over SC. Conversely, during years with negative precipitation anomalies in P2, these processes occur in reverse. The enhanced interannual variability of local convective activity from P1 to P2 leads to a corresponding increase in the interannual variability of the WPSH, which, coupled with an amplified interannual variability of SRP, results in heightened interannual variability of SIPI. Additionally, the composite analysis of 30-90-day ISO events further substantiates the underlying mechanisms driving the interdecadal amplification of SIPI interannual variability. Diagnostic results reveal that the 30-90-day horizontal wind induces heightened convergence of background moisture over SC. Precipitation in South China is prevalent and primarily occurs from April to September, leading to significant enormous economic losses and casualties due to flood disasters almost every year during this period. Influenced by the East Asian summer monsoon, summer precipitation in South China exhibits diverse variabilities at multiple scales, including interdecadal, interannual, intraseasonal and synoptic variability. Moreover, the intraseasonal variability of precipitation in South China holds great importance for extended-range forecasting and has been extensively investigated. With in-depth research, it has been revealed that there are also significant physical laws governing the long-term variations in intraseasonal precipitation. This study focuses on investigating the interdecadal changes in the interannual variability in summertime intraseasonal precipitation intensity over South China during the past four decades and exploring the potential underlying mechanisms. The findings can enhance our comprehension of the mechanisms driving long-term variations in intraseasonal precipitation pattern in South China. The interannual variability of 30-90-day summer intraseasonal precipitation over South China exhibited an increase in the mid-1990s The Silk Road pattern (SRP) and the western Pacific subtropical high (WPSH) primarily contribute to this increase The occurrence of SRP and WPSH anomalies is modulated by SST warming in the North Atlantic and the equatorial East Pacific, respectively