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The Asian summer monsoon (ASM) is a vast climate system, whose variability is critical to the livelihoods of billions of people across the Asian continent. During the past half-century, much progress has been made in understanding variations on a wide range of timescales, yet several significant issues remain unresolved. Of note are two long-standing problems concerning orbital-scale variations of the ASM. (1) Chinese loess magnetic susceptibility records show a persistent glacial-interglacial dominated ~100 kyr (thousand years) periodicity, while the cave oxygen-isotope (δ18O) records reveal periodicity in an almost pure precession band (~20 kyr periodicity)—the “Chinese 100 kyr problem”. (2) ASM records from the Arabian Sea and other oceans surrounding the Asian continent show a significant lag of 8–10 kyr to Northern Hemisphere summer insolation (NHSI), whereas the Asian cave δ18O records follow NHSI without a significant lag—a discrepancy termed the “sea-land precession-phase paradox”. How can we reconcile these differences? Recent and more refined model simulations now provide spatial patterns of rainfall and wind across the precession cycle, revealing distinct regional divergences in the ASM domain, which can well explain a large portion of the disparities between the loess, marine, and cave proxy records. Overall, we also find that the loess, marine, and cave records are indeed complementary rather than incompatible, with each record preferentially describing a certain aspect of ASM dynamics. Our study provides new insight into the understanding of different hydroclimatic proxies and largely reconciles the “Chinese 100 kyr problem“ and “sea-land precession-phase paradox”.

The interannual teleconnections between the summer North Atlantic Oscillation and summer precipitation in eastern China over the last millennium are investigated in a 1,000‐year simulation by the global climate model Community Climate System Model version 2.0.1. The model was able to roughly produce the general features of the teleconnection influences in eastern China, with negative (positive) precipitation anomalies north of 30°N and positive (negative) precipitation anomalies south of 30°N, associated with the positive (negative) phase of the North Atlantic Oscillation. The composite analysis reveals that the influence of the North Atlantic Oscillation on precipitation in summer in eastern China is chiefly via the “North Atlantic‐Eurasian teleconnection pattern,” which extends from the subtropical North Atlantic to East Asia. The impacts of the North Atlantic Oscillation on the climate in eastern China have been highlighted over the last decade. Recently, the observed impacts of the North Atlantic Oscillation on precipitation in eastern China in summer, chiefly via the “North Atlantic‐Eurasian teleconnection pattern,” have been noted. This pattern propagates along a high‐latitude pathway and is different from the midlatitude circumglobal teleconnection pattern. Here this teleconnection pattern is investigated in a millennium context using a 1,000‐year simulation of the Community Climate System Model version 2.0.1. The model results reveal that the simulated NAO‐related teleconnection pattern during the summer season is very similar to the observed pattern. Along its path through Eurasia, a positive NAO index causes anomalously high sea level pressures and 500‐hPa geopotential heights over Mongolia‐north China that correspond to the anomalous anticyclone in the 850‐hPa wind anomalies and hence cause reduced precipitation in north China. The opposite occurs during negative summer NAO phases. The model's teleconnection patterns of the summer NAO capture the reconstructed and observed patterns of the summer precipitation changes in eastern China and provide further evidence for the climate model‐based implications for predictions and future projections of seasonal precipitation in eastern China. Simulated impacts of the NAO on the interannual variability of precipitation in summer in eastern China are investigatedThe model CCSM 2.0.1 was able to roughly produce the general features of the teleconnection climate influences in eastern ChinaPrecipitation anomalies in eastern China associated with the summer NAO are linked to the “North Atlantic‐Eurasian teleconnection pattern”

The Interdecadal Pacific Oscillation (IPO) and its impacts on precipitation over eastern China during the last millennium are investigated through analyzing two 1000 year global climate model simulations. Results show that the model does not simulate a prolonged period of negative IPO before A.D. 1300 suggested by the proxy reconstruction, although it does simulate centennial periods of negative and positive IPO. The simulated IPO exhibits several low‐frequency oscillations, including 10–23, 30–33, 35–70, and 85–110 years. However, it remains an open question whether simulated IPO oscillations longer than bidecadal mode can be or not be considered as essentially internal modes of variability. The simulations indicate that precipitation over eastern China is associated with the IPO. When the strongest IPO signal of 53–77 year oscillation occurs, the summer precipitation goes of opposite sign over North China (NC) and the middle and lower Yangtze River Vally (MLYRV), i.e., dipole mode such as the “flood‐in‐south and drought‐in‐north” pattern that occurs during the positive IPO episodes and vice versa. While coherent mode is dominant when the relatively weak IPO signal occurs, and warm phases of the IPO coincide with coherent drought and vice versa. The association between 53–77 year oscillation of the IPO and precipitation in NC is more marked than that in the MLYRV. Our results suggest that the internal variability of climate system like the IPO may play an important role in precipitation over eastern China, at least on the 53–77 year oscillation. The IPO and its impacts are investigated in two 1000 year climate simulationsThe general features of IPO variability are not simulated by the modelThe correlation of east China's rainfall with the IPO exhibits a dipole pattern

Severe persistent drought events during the last 530 years are examined in Arid Central Asia (ACA) by using the data with proxy assimilation from the Last Millennium Climate Reanalysis project version 2.0 (LMR v2.0). According to the results from the LMR v2.0, six severe decadal droughts occurred in ACA during the last 530 years and five of them overlap with the results based on the independent reconstructions of Asian summer precipitation, such as the droughts of 1519–1538 CE, 1545–1561 CE, 1621–1658 CE, 1822–1846 CE, and 1964–1983 CE. The climate anomaly patterns are characterized by opposite anomalies between the high‐latitude and midlatitude Eurasia during the first four well‐agreement droughts, with negative precipitation and positive surface level pressure and 500‐hPa geopotential height anomalies located over midlatitude Eurasia and opposite anomalies over high‐latitude Eurasia. Whereas, during the last well‐agreement drought, opposing pattern of the climate variation observed between in ACA and in the Mediterranean with negative precipitation anomalies and positive 500‐hPa geopotential height anomalies in ACA and opposite anomalies in the Mediterranean. The positive Arctic Oscillation/North Atlantic Oscillation influence is found to dominate the droughts of 1621–1658 CE via a northward migration of the westerlies. While the last drought of 1964–1983 CE produced by the combined impacts of the negative Atlantic Multidecadal Oscillation and Pacific Decadal Oscillation via the Silk Road pattern over the midlatitude Eurasian continent. The LMR v2.0 was able to roughly capture five severe decadal droughts occurred in ACA during the last 530 yearsThe climate anomaly patterns over Eurasia during the first four droughts are different with these patterns during the last droughtThe positive AO/NAO influences dominate the drought of 1621–1658 CE, while the negative AMO and PDO played import role on the last drought The LMR v2.0 was able to roughly capture five severe decadal droughts occurred in ACA during the last 530 years The climate anomaly patterns over Eurasia during the first four droughts are different with these patterns during the last drought The positive AO/NAO influences dominate the drought of 1621–1658 CE, while the negative AMO and PDO played import role on the last drought

Decadal–centennial hydroclimate variability over eastern China during the last millennium is investigated using the product of Paleo Hydrodynamics Data Assimilation (PHYDA). Results reveal that the PHYDA depicts a more homogeneous temporal pattern during the early part of the Little Ice Age with other reconstructions than those during the other periods, and could also identify the droughts of 1352–90 AD, 1445–98 AD, 1580–94 AD, and 1626–65 AD during this period. On centennial time scales, the PHYDA shows that the linkage between the Palmer drought severity index over eastern China and the Atlantic Multidecadal Oscillation (AMO) index is more marked than that with the El Niño–Southern Oscillation and the location of the intertropical convergence zone over the Asian–Australian monsoon area during the period after the 1350s. For the decadal droughts, the PHYDA suggests most of the drought events during the last millennium were linked to the El Niño–like mean states and the negative AMO states.