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The decadal variability of the Asian monsoon is a key variation in long-term climate mean and an important background for accurately estimating its annual variability. Therefore, the decadal variability of the Asian monsoon is crucial for predicting the medium- to long-term climate changes of the Asian monsoon region. The study of its evolutionary patterns and dynamic mechanisms is closely related to the needs of national medium- to long-term development decisions and the environmental, economic, and social development of the Asian monsoon region. It is also at the forefront of international climate research. By combining modern observations, climate reconstruction from proxy data (such as historical documents, tree rings, lake sediments, and stalagmites), and climate model simulation data, this paper reviews the characteristics of the decadal variability of the East Asian summer monsoon in different periods. This paper also summarizes the impact mechanisms of internal climate variability, such as the Atlantic Multidecadal Variability (AMV) and Pacific Decadal Variability (PDV), and external forcing factors, such as volcanic activity, solar radiation, and anthropogenic activities, on the decadal variability of the East Asian summer monsoon. First, we collected published high-resolution (>7 years) East Asian summer monsoon records based on historical documents, tree rings, and speleothem dat covering the past 2000 years, along with the latest climate simulation results for the past millennium. We then detrended the data and applied an 11-year low-pass filter, before using a multi-taper method (MTM) spectral analysis to examine their periodic characteristics. Both reconstruction and simulation results indicated that the East Asian summer monsoon over the past millennium has exhibited decadal characteristics with dominant periods of 20-30 years and 60-80 years, which is consistent with instrumental records of the past century. The periodic characteristics of historical documents, tree rings, and lake sediment records showed obvious spatial differences, reflecting the spatial variability of East Asian monsoon precipitation. However, the periodic characteristics of stalagmites in the entire East Asian monsoon region showed significant spatial consistency, reflecting the circulation characteristics of the East Asian summer monsoon with widespread consistency on a large scale. This periodic characteristic is consistent with the dominant periods of AMV and PDV, indicating the potential influence of AMV and PDV on the decadal variability of the East Asian summer monsoon. Finally, we discuss the driving mechanisms behind the decadal climate variability of the East Asian summer monsoon from both internal and external perspective. Modern meteorological analysis showed that AMV and PDV can affect the East Asian summer monsoon circulation and precipitation through atmospheric teleconnection wave patterns, influencing large-scale ocean-atmosphere coupling processes and modulating El Niño-Southern Oscillation variability. Natural external forcing factors, such as volcanic activity and solar radiation, and anthropogenic external forcing factors, such as greenhouse gas and aerosol emissions, directly or indirectly influence the interdecadal variability of the East Asian summer monsoon by modulating internal climate system variability. However, the following key scientific questions remain to be answered: Which is more dominant between internal variability and external forcing? What are the specific mechanisms involved? How will the interdecadal variability of the East Asian summer monsoon and precipitation patterns change in the future under different climatic background conditions? Research on the decadal variability of the East Asian monsoon under different climatic background conditions, combined with numerical simulations, is expected to provide important references for a deeper understanding of these issues.
Wang et al. (Mon,) studied this question.