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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°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. Plain Language Summary: 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. Key Points: The interannual variability of 30–90‐day summer intraseasonal precipitation over South China exhibited an increase in the mid‐1990sThe Silk Road pattern (SRP) and the western Pacific subtropical high (WPSH) primarily contribute to this increaseThe occurrence of SRP and WPSH anomalies is modulated by SST warming in the North Atlantic and the equatorial East Pacific, respectively [ABSTRACT FROM AUTHOR]

In this study, a 55‐year climate simulation over East Asia is conducted by using the regional climate model RegCM4.6 and the variations of biases in different climate backgrounds are investigated. The results show that the biases of rainfall and western Pacific subtropical high (WPSH) simulated by RegCM4.6 are not stable, instead they exhibit an obvious feature of interdecadal variation that is similar to the interdecadal variation of rainfall and WPSH themselves. The interdecadal change of the simulation bias occurs in the late 1970s, when abrupt interdecadal changes took place in global atmosphere and ocean as well as in East Asia climate. The interdecadal variation of the bias of the simulated WPSH is closely related with the interdecadal variation of the simulated rainfall bias. After 1978, the simulated WPSH is displaced further south than the observed WPSH, leading to excessive rainfall in the simulation and larger positive bias in south China. These overestimated rainfall and convective clouds in south China during 1979–2009 consume a lot of water vapour in the atmosphere and weaken the downwards solar radiation, resulting in a cold and dry atmosphere and large negative biases of virtual temperature and geopotential height at 500 hPa (H500) during 1979–2009 compared to that during 1955–1978. Corresponding to the above circulation anomalies, the simulated WPSH further weakens and shifts southwards after the late 1970s. A positive feedback loop is formed due to the positive feedback between the WPSH and cumulus convective process. [ABSTRACT FROM AUTHOR]

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°E and 160°E and west of 80°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°N, an anomalous moist ascending flow develops over the YHRV at around 35°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. [ABSTRACT FROM AUTHOR]

ABSTRACT This study investigates, under El Niño/La Niña conditions, the effects of sea surface temperature anomaly ( SSTA) in the East Indian Ocean ( EIO) on tropical cyclone ( TC) genesis over the western North Pacific ( WNP), and a possible mechanism is proposed. It is found that the EIO SSTA exerts a secondary modulation to cyclogenesis relative to the El Niño-Southern Oscillation ( ENSO), and the negative correlation between the EIO SSTA and WNP TC frequency is significantly weakened by the ENSO events. Under El Niño (La Niña) conditions, no matter what phases of EIO SSTA, TC genesis generally shows similar features with low (high) frequency in the western-central WNP (15°-25°N, 120°-150°E) and high (low) frequency in the southeastern WNP (5°-15°N, 150°-170°E). In particular, the effects of warm EIO SSTA on the WNP TC activity represent an asymmetry between El Niño and La Niña. That is, the warm EIO SSTA and El Niño share combined effects to decrease TC genesis over the western-central WNP. By contrast, under La Niña conditions, the influence of warm EIO SSTA on TC activity over the western-central WNP is partially drown out by La Niña. Meanwhile, weaker monsoon trough with intense anomaly of easterly jointly induced by the two factors suppresses TC genesis over the southeastern WNP. [ABSTRACT FROM AUTHOR]

Based on the simple ocean data assimilation (SODA) reanalysis dataset from the University of Maryland and the method of Empirical Orthogonal Functions (EOF), the characteristics of interannual and interdecadal variabilities of the equatorial Pacific subsurface oceanic temperature anomaly (SOTA) are captured. The first and second modes of the equatorial Pacific SOTA in the interannual and interdecadal variations are found respectively and the effect of the second mode on the ENSO cycle is discussed. Results show that the first mode of SOTA's interannual and interdecadal variabilities exhibit a dipole pattern, indicating that the warm and cold temperature anomalies appear simultaneously in the equatorial subsurface Pacific. The second mode shows coherent large-scale temperature anomalies in the equatorial subsurface Pacific, which is a dominant mode in the evolution of ENSO cycle. The temporal series of the second mode has a significant lead correlation with the Niño-3.4 index, which can make a precursory prediction signal for ENSO. The function of this prediction factor in SOTA is verified by composite and case analyses. [ABSTRACT FROM AUTHOR]