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This work analyzes and discusses the influence of human activities on the meteorological conditions related to winter haze events in Beijing, Tianjin, and Hebei (i.e., the Jing–Jin–Ji region) during 1961–2016, using the results of two numerical simulation experiments based on the Community Atmosphere Model version 5.1.1 (http://www.cesm.ucar.edu/models/cesm1.0/cam/docs/ug5_1_1/book1.html) used in the international Climate Variability and Predictability Programme (CLIVAR) Climate of the 20th Century. Detection and Attribution Project (C20C+ D&A). The results show that, under the influence of human activities, the changes in dynamical and thermal meteorological conditions related to winter haze events in the Jing–Jin–Ji region are conducive to the formation and accumulation of haze, and prevent the diffusion of pollutants. The dynamical conditions mainly include the obvious weakening of the East Asian winter monsoon (EAWM) and the enhancement of the near-surface anomalous southerly wind. The thermal conditions include the obvious increase in surface temperature, and the enhancement of water vapor transport and near-surface inversion. The relative contribution of dynamical and thermal conditions to the variation of haze days in the Jing–Jin–Ji region is analyzed using statistical methods. The results show that the contribution of human activities to the increase of haze days in the Jing–Jin–Ji region is greater than that of natural forcing for the study period. To be specific, the dynamical meteorological factors contribute more to the haze days than the thermal meteorological factors. The contribution of thermal meteorological factors is basically the same in both scenarios.

The East Asian winter monsoon in 2018 winter is characterized by below-normal surface air temperature (SAT) over central Siberia and eastern China when the winter mean is considered and by three cold waves when the intraseasonal variability, whose timescale is shorter than a season, is concerned. The three cold waves only consist of approximately 2 weeks, but they play a primary role in shaping the SAT pattern in the winter mean field. Nevertheless, the atmospheric circulation anomalies that shape the SAT pattern during the cold waves cannot be reflected well in the winter mean fields. It leads to insufficiencies to explain the winter mean SAT pattern by examining the winter mean circulation alone. In contrast, the SAT pattern formation can be better interpreted when the role of cold waves is considered. These results suggest that the common approach in climate science to examine the seasonal mean variables alone in understanding the seasonal behaviors of climate misses some crucial aspects, at least for this particular winter, and that the intraseasonal variability should be taken into account to supplement these missing aspects. It is recommended that the influences of intraseasonal variability on the climatic behavior of the East Asian winter monsoon be studied comprehensively in the future to portrait a complete picture of this issue.

In the East Asian monsoon area, stalagmites generally record lower and higher oxygen isotope (δ18O) levels during warm humid interglacial and cold dry glacial periods, respectively. Here, we report unusually low stalagmite δ18O from the last glacial period (ca. 32.2–22.3 ka) in Fukugaguchi Cave, Niigata Prefecture, Japan, where a major moisture source is the East Asian winter monsoon (EAWM) that carries vapor from the warm surface of the Japan Sea. The δ18O profile of this stalagmite may imply millennial-scale changes, and high δ18O intervals that are related to Dansgaard–Oeschger (D–O) interstadials. More importantly, the stalagmite exhibits low overall δ18O values; the mean δ18O (− 8.87‰) is distinctly lower than the mid-Holocene mean of another stalagmite from the same cave (4.2–8.2 ka, − 7.64‰). An interpretation assuming a more intense EAWM and greater vapor transportation during the last glacial period, compared with the mid-Holocene, contradicts the limited inflow of the Tsushima Warm Current into the Japan Sea because of lowered sea level. Additionally, our model calculation using δ18O data from meteoric water indicated that the amount effect of winter meteoric water was insignificant (1.2‰/1000 mm). Low stalagmite δ18O for the last glacial period in Fukugaguchi Cave most likely resulted from 18O-depleted surface water, which developed in the isolated Japan Sea. The estimated amplitude of the δ18O decrease in surface water was ~ 3‰ at most, consistent with the abnormally low values for foraminifera (by ~ 2.5‰) in sediment during the last glacial period, shown by samples collected from the Japan Sea. This is the first terrestrial evidence of 18O depletion in Japan Sea surface water during the last glacial period.

Extremely cold temperatures are a significant threat to agriculture and transportation in winter in southeastern China. However, due to the shortness of instrumental records and the scarcity of long-term temperature reconstructions, more high-quality temperature reconstructions are still needed to fully examine their spatial-temporal variability over the past several centuries. In this study, we built an earlywood width (EWW) chronology, a latewood width (LWW) chronology, and a tree-ring width (TRW) chronology using tree-ring samples of Pinus taiwanensis Hayata from the western Tianmu Mountains and the Xianyu Mountains in southeastern China. The tree growth-climate relationships were analyzed, and we found the strongest correlation between December and March mean temperature and the EWW chronology. The December-March mean temperature history was then reconstructed over the period of 1871-2016 using a linear regression model, which is the first EWW-based temperature reconstruction in southeastern China. With a higher explained variance (47.0%) than that (31.7%) of a previous reconstruction using a TRW chronology, the quality of the model has largely improved. This reconstruction was also comparable with other nearby records, further demonstrating the reliability of our new model. Furthermore, our reconstruction exhibits a significantly negative relationship with the East Asian winter monsoon index (EAWMI) since the 1920s, which may be attributed to the obviously enhanced EAWMI thereafter.

The present study investigates different impacts of the East Asian winter monsoon (EAWM) on surface air temperature (Ts) in North America (NA) during ENSO and neutral ENSO episodes. In neutral ENSO years, the EAWM shows a direct impact on the Ts anomalies in NA on an interannual time scale. Two Rossby wave packets appear over the Eurasian–western Pacific (upstream) and North Pacific–NA (downstream) regions associated with a strong EAWM. Further analysis suggests that the downstream wave packet is caused by reflection of the upstream wave packet over the subtropical western Pacific and amplified over the North Pacific. Also, the East Asian subtropical westerly jet stream (EAJS) is intensified in the central and downstream region over the central North Pacific. Hence, increased barotropic kinetic energy conversion and the interaction between transient eddies and the EAJS tend to maintain the circulation anomaly over the North Pacific. Therefore, a strong EAWM tends to result in warm Ts anomalies in northwestern NA via the downstream wave packet emanating from the central North Pacific toward NA. A weak EAWM tends to induce cold Ts anomalies in western-central NA with a smaller magnitude. However, in ENSO years, an anomalous EAJS is mainly confined over East Asia and does not extend into the central North Pacific. The results confirm that the EAWM has an indirect impact on the Ts anomalies in NA via a modulation of the tropical convection anomalies associated with ENSO. Our results indicate that, for seasonal prediction of Ts anomalies in NA, the influence of the EAWM should be taken into account. It produces different responses in neutral ENSO and in ENSO years.

The temperature proxies U 37 K ′ , LDI, TEX 86 H , and RI-OH are derived from lipid biomarkers, namely long-chain alkenones from coccolithophorids and long-chain diols ascribed tentatively to eustigmatophytes, as well as glycerol dialkyl glycerol tetraethers (GDGTs) and OH-GDGTs produced by Archaea. The applicability of these proxies in the South China Sea (SCS) has been investigated previously. However, in each study only one or two of the proxies were compared, and the recently updated calibrations or new calibrating methods such as BAYSPAR and BAYSPLINE were not applied. Here, we investigate four proxies in parallel in a set of surface sediment samples from the northern SCS shelf and relate them to local sea surface temperature (SST), which allows for us to compare and assess similarities and differences between them and also help improve regional multiproxy seawater temperature reconstructions. Our results indicate that U 37 K ′ reflects annual mean SST with a slight bias toward the warm season. Terrestrial inputs appear to have a significant impact on LDI, TEX 86 H , and RI-OH proxies near the coast, leading to colder LDI- and TEX 86 H -derived temperatures but a warmer RI-OH temperature estimate. After excluding samples influenced by terrestrial materials, we find that LDI-derived temperature agrees well with annual SST, while TEX 86 H - and RI-OH-derived temperature estimates are close to SSTs in seasons dominated by the East Asian winter monsoon and summer monsoon, respectively. The different seasonal biases of these temperature proxies provide valuable tools to reconstruct regional SSTs under different monsoonal conditions.

Sub-orbital-scale variations of the East Asian winter monsoon (EAWM) and its mechanisms during the Holocene are controversial, partly due to the lack of high-quality records from Chinese loess. Here, we present high-resolution reconstruction of Holocene EAWM intensity based on optically stimulated luminescence dating and grain-size analysis from three loess sections taken from the Chinese Loess Plateau. The EAWM showed a persistent weakening trend during the early Holocene (ca. 11.7–6.5 kyr B.P.) and a strengthening trend during the mid- to late Holocene (since ca. 6.5 kyr B.P.). We propose that this was caused by changes in high-latitude Northern Hemisphere ice volume and middle- to high-latitude Northern Hemisphere atmospheric temperatures, respectively. We also observed an anti-correlation between EAWM and East Asian summer monsoon. Our findings provide a robust solution to the debate regarding Holocene EAWM changes and contribute to the understanding of potential future variations in EAWM intensity.

Previous studies have revealed that the relationship between the El Niño–Southern Oscillation (ENSO) and the East Asian winter monsoon (EAWM) is not statistically significant when the Pacific Decadal Oscillation (PDO) is in its positive phase. This study explores a possible way to obtain a robust ENSO–EAWM relationship from a dynamical point of view. Here, the authors show that the East Asian winter temperature is significantly and continuously correlated with ENSO when the linear impact of the PDO has been linearly removed from ENSO. Such a conclusion is confirmed by different reanalysis datasets. The dynamical process intensifying the ENSO–EAWM is further investigated from the perspective of whether or not the atmospheric teleconnection between the Pacific and East Asia has established. Compared to the situation associated with the original ENSO in the positive phase of the PDO, the Walker circulation associated with the processed ENSO, from which the effect of North Pacific climate systems has been removed, tends to exert a more pronounced influence on the atmospheric circulation over the western North Pacific. Consequently, an anomalous anticyclone emerges in the Kuroshio extension. In this sense, the Pacific–East Asian teleconnection is also well established during the positive phase of the PDO, which favors the impact of ENSO on East Asian winter temperature.

Future projection of diffusion conditions associated with extreme haze events over eastern China is of great importance to government emission regulations and public human health. Here, the diffusion conditions and their changes under future warming scenarios are examined. The relative strength of haze events in the Northern China Plain region increase from 150% during 2006–15 to 190% during 2090–99 under RCP8.5 scenarios, induced by a stronger and longer-lasting anticyclone anomaly in eastern China. The strengthened anticyclone anomaly is mainly induced by increased northern wave train convergence emanating from the Barents–Kara Sea, and the longer duration of the anticyclone anomaly is mainly induced by stronger local feedback that can extract more energy from the basic state to maintain the anticyclone anomaly in eastern China. Aerosol reduction is found to play a dominant role in strengthening the upstream wave train near the Barents–Kara Sea and the downstream anticyclone in eastern China, while the effects from increased greenhouse gases are small. The results of this study indicate that future aerosol emissions reduction can induce deteriorating diffusion conditions, suggesting more stringent regulations on aerosol emissions in China are needed to meet air quality standards.

The Japan Sea was a semi-closed marginal sea mainly connected to the subarctic northwestern Pacific via shallow seaways during the late Miocene. We use a multiple regression analysis with common extant radiolarian species groups to estimate the sea-surface temperature (SST) for the period between 9.1 and 5.3 Ma. Our results show a cooling of 8 °C between 7.9 and 6.6 Ma, when the SST dropped from 24 °C to 16 °C. We infer that this cooling dominantly reflects wintertime cooling related to an intensified East Asian winter monsoon. On the other hand, cooling of the summertime SST occurred from 6.6 to 5.8 Ma, suggesting that the late Miocene global cooling is composed of a wintertime cooling phase from 7.9 to 6.6 Ma and summertime cooling phase from 6.6 to 5.8 Ma.

This study investigates the modulation of North Pacific Oscillation (NPO) variability upon initiation of the East Asian winter monsoon (EAWM). The data show that the initiation of EAWM in the Philippine Sea strongly connects to the southern lobe variability of the NPO in January followed by a basin-scale oceanic Victoria mode pattern. No apparent connection was found for the northern lobe of the NPO when the ENSO signals are removed. The strengthening of the EAWM in November interacts with the Kuroshio front and generates a low-level heating source in the Philippine Sea. Significant Rossby wave sources are then formed in the lower to midtroposphere. Wave ray tracing analyses confirm the atmospheric teleconnection established by the Rossby wave propagation in the mid- to upper troposphere. Analyses of the origin of wave trajectories from the Philippine Sea show a clear eastward propagating pathway that affects the southern lobe of the NPO from the southern lobe of the western Pacific pattern at 500 hPa and above on the time scale of 20 days. No ray trajectories from the lower troposphere can propagate eastward to influence the central-eastern subtropical Pacific. The wave propagation process is further supported by the coupled model experiments.

Previous research work found that two distinct surface air temperature (SAT) modes—the northern (N-) and the southern (S-) modes dominate the East Asian winter monsoon (EAWM) region. The inter-annual variations of these two modes were mainly attributed to preceding Siberian snow cover anomalies and El Nino–Southern Oscillation (ENSO). Observed evidence in this study shows that sea ice anomalies on Barents–Kara (BK) and Laptev Seas and those on Chukchi–Beaufort (CB) Sea in autumn have co-mingled effects on the two abnormal EAWM modes. If negative sea ice anomalies appear in the BK and northern CB Sea in September–October (SO), the following winter SAT anomaly over East Asia is featured by an obvious cooling north of 40° N, which highly resembles the SAT N-mode of EAWM. If negative sea ice anomalies occur in BK–Laptev Sea but positive anomalies in the southern CB Sea, the East Asia winter SAT anomaly exhibits a salient cold condition over the south of 40° N and corresponds to the EAWM S-mode. The above results indicate that autumn Arctic sea ice can provide another predictability source for the EAWM, besides Siberian snow cover and ENSO. To further verify its contribution to seasonal prediction of the EAWM, a series of physical–empirical models are established using the combinations of SO Arctic sea ice, autumn Siberian snow cover and ENSO. Hindcast experiment output shows when adding autumn Arctic sea ice into the predictors, the cross-validated prediction skill is significantly improved. The possible physical mechanisms on how preceding Arctic sea ice anomalies impact on the N- and S- modes are also discussed.

In this study, focusing on the interdecadal time scale, we investigate the internal variability of the East Asian winter monsoon (EAWM) using output from 19 coupled models’ long-term preindustrial control (piControl) simulations within phase 5 of the Coupled Model Intercomparison Program (CMIP5). In total, we identify 53 cases of significant interdecadal weakening of the EAWM from these 19 piControl simulations. In most weakening cases, both the Siberian high and the East Asian trough are significantly weakened. The East Asian jet stream in the upper troposphere shifts poleward. Southerly wind anomalies are evident over East Asia in the lower troposphere. At the same time, both the Arctic Oscillation (AO) and the North Pacific Oscillation are in their positive phases. Associated anomalous anticyclonic circulation can be found over the North Pacific. Additionally, the North Pacific shows negative Pacific decadal oscillation (PDO)-like sea surface temperature (SST) anomalies. In contrast, we also analyzed 49 cases of significant strengthening of the EAWM, and the atmospheric and oceanic anomalies show opposite signals with the weakening cases. This suggests that internal variabilities of the climate system can also cause interdecadal variations of the EAWM. In addition, the phase shifting of the AO is likely the main reason for the EAWM’s interdecadal variations in the unforced long-term simulations. Further numerical experiments using the Community Atmosphere Model, version 4 (CAM4), deny the causal relationship between the interdecadal variations of EAWM and PDO-like SST anomalies. This study also implies that the internal variabilities of the climate system could contribute to the observed interdecadal weakening of the EAWM around the mid-1980s.

The decadal variability of ocean primary productivity (PP) has mainly been studied using relatively short term satellite data, limiting its in-depth analysis. Here, by removing the influence of the C Suess effect, we extract the PP signal on decadal timescales using a record of coral δC values from the northern South China Sea (NSCS), where the physical-biogeochemical conditions are influenced largely by the winter monsoon. Our results show that the PP in the NSCS increased from 1851 to the 1920s and decreased from the 1920s to 2007, and large superimposed decadal-scale changes were observed. The in-phase relationship observed between the PP reconstruction and winter monsoon records suggests that the changes in the PP in the NSCS are linked to decadal-scale changes in the winter monsoon. Considering that the winter monsoon intensity may weaken in the future under global warming, the PP in the NSCS might decrease in the coming decades.

The prediction skill for the East Asian winter monsoon (EAWM) in early (November–December, ND) and late winter (January–February, JF) is investigated based on the NCEP’s Climate Forecast System, version 2 (CFSv2), at different lead months. Results show that the prediction skill of ND-EAWM is higher than that of JF-EAWM. ND-EAWM can be reasonably reproduced by CFSv2 with initial conditions from the previous May to November, whereas with initial conditions from the previous July to January it has little forecasting skill for predicting JF-EAWM. The difference in the impacts of ENSO between early and late winter may influence the ENSO–EAWM relationship and cause the subseasonal change. As the seasonality of the ENSO cycle changes from early winter to late winter, the anomalous tropical east–west Walker circulation system shifts from a double-cell to a single-cell regime. The double-cell regime in early winter is usually accompanied by intense tropical convection localized in the Maritime Continent. ENSO-related anomalous convection strongly influences the EAWM through a systematic wave train pattern. However, ENSO cannot easily influence the EAWM in late winter through this process when the turnabout of ENSO commences in late winter. CFSv2 can successfully reproduce this physical process of ENSO affecting the EAWM in early winter. It is also found that the year-to-year increment approach may enhance the skill of CFSv2 in predicting the EAWM in late winter.

The Model for Prediction Across Scales (MPAS) is used to simulate the East Asian winter monsoon (EAWM) over the 2011–2020 winter. The 45 day hindcasts are made with 30 km horizontal resolution and constructed to a time-lagged ensemble system. The climatology, the major modes of EAWM variability, and the blocking activities are examined. The evaluation results reveal that MPAS can simulate the climatologic characteristics of EAWM reasonably, with a surface cold bias of 4% and a positive rainfall bias of 9% over East Asia. MPAS can perform skillfully in the forecasts of surface temperature probability of East Asia and is more reliable in detecting below normal and above normal events. The features that influence the EAWM variability are also analyzed. MPAS simulates reasonably in the occurrence frequency of blocking high in both locations and duration time. The empirical orthogonal function analysis also shows that MPAS can capture the two major modes of the surface temperature of EAWM. On the other hand, it is also found that a biased sea surface temperature may modify the circulations over the Western Pacific and affect the simulated occurrence frequency of cold events near Taiwan during winter.

The present study investigates the impacts of autumn-winter Tibetan Plateau (TP) snow cover anomalies on the interannual variability of the East Asian winter monsoon (EAWM). It is found that the northern component of EAWM is significantly associated with October-November-December-January (ONDJ) snow cover anomalies over the eastern TP, whereas the TP snow cover changes have little impact on the southern component of EAWM. However, the relationship of the northern component of EAWM to ONDJ TP snow cover experienced an obvious change in the mid-1990s. During 1979–1998, due to the high persistence of TP snow anomalies from autumn to winter, extensive ONDJ TP snow cover anomalies have a prominent influence on atmospheric circulation over Asia and the North Pacific, with more TP snow cover followed by an enhanced Siberian high and a deepened Aleutian low in winter, resulting in stronger EAWM. During 1999–2016, TP snow cover anomalies have a weak persistence. The atmospheric circulation anomalies display a different distribution. As such, there is a weak connection between the northern component of EAWM and the TP snow cover anomalies during this period.

This research investigates the impact of local sea surface temperature (SST) on the 2-month (January and February) accumulated snowfall over the Yeongdong (YD) region. The YD region is strongly affected by synoptic-scale factors such as the East Asian winter monsoon (EAWM). The relationships of snowfall over the YD region to the EAWM and local SST are examined based on observational analyses and sensitivity experiments using a regional climate model. In the sensitivity experiments, local SST is replaced with the 33-yr mean winter SST (1982–2014). The observational analysis shows that both the synoptic environment and local SST are important factors for the occurrence of anomalous heavy snowfall over the YD region. The favorable synoptic environments can be characterized by eastward expansion of the Siberian high over Manchuria and corresponding enhancement of easterly anomalies over the YD region. These conditions are more frequently observed during the weak EAWM years than during the strong EAWM. Furthermore, warm SST over the East Sea contributes to heavy snowfall over the YD region by providing heat and moisture in the lower troposphere, which are important sources of energy for the formation of heavy snowfall. Warm SST anomalies over the East Sea enhance low-level moisture convergence over the YD region, while cold SST anomalies lead to reduced moisture convergence. Sensitivity experiments indicate that local SST can significantly affect snowfall amount over the YD region when the synoptic environments are favorable. However, without these synoptic conditions (expansion of the Siberian high and easterly inflow), the impact of local SST on the snowfall over the YD region is not significant.

The present study investigates the impacts of the North Atlantic sea surface temperature (SST) anomalies on the East Asian winter monsoon (EAWM) variability. It is found that the northern component of the EAWM variability is associated with a dipole pattern of preceding summer North Atlantic SST anomalies during 1979–2016. The processes linking preceding summer North Atlantic SST to EAWM include the North Atlantic air–sea interactions and atmospheric wave train triggered by the North Atlantic SST anomalies. Atmospheric wind anomalies in the preceding spring–summer result in the formation of a dipole SST anomaly pattern through surface heat flux changes. In turn, the induced SST anomalies provide a feedback on the atmosphere, modifying the location and intensity of anomalous winds over the North Atlantic. The associated surface heat flux anomalies switch the North Atlantic SST anomaly distribution from a dipole pattern in summer to a tripole pattern in the following winter. The North Atlantic tripole SST anomalies excite an atmospheric wave train extending from the North Atlantic through Eurasia to East Asia in winter, resulting in anomalous EAWM. However, the relationship of the northern component of EAWM to preceding summer North Atlantic SST anomalies is weak before the late 1970s. During 1956–76, due to weak air–sea interaction over the North Atlantic, no obvious tripole SST anomaly pattern is established in winter. The atmospheric wave train in winter is located at higher latitudes, leading to a weak connection between the northern component of EAWM and the preceding summer North Atlantic dipole SST anomaly pattern.

Located in a monsoon domain, East Asia suffers devastating natural hazards induced by anomalous monsoon behaviors. East Asian monsoon (EAM) research has traditionally been a high priority for the Chinese climate community and is particularly challenging in a changing climate where the global mean temperature has been rising. Recent advances in studies of the variabilities and mechanisms of the EAM are reviewed in this paper, focusing on the interannual to interdecadal time scales. Some new results have been achieved in understanding the behaviors of the EAM, such as the evolution of the East Asian summer monsoon (EASM), including both its onset and withdrawal over the South China Sea, the changes in the northern boundary activity of the EASM, or the transitional climate zone in East Asia, and the cycle of the EASM and the East Asian winter monsoon and their linkages. In addition, understanding of the mechanism of the EAM variability has improved in several aspects, including the impacts of different types of ENSO on the EAM, the impacts from the Indian Ocean and Atlantic Ocean, and the roles of mid- to high-latitude processes. Finally, some scientific issues regarding our understanding of the EAM are proposed for future investigation.

The middle-Pleistocene Xiashu loess deposit in the lower reaches of the Yangtze River (LRYR), southern China, may yield evidence with significant climatic and environmental significance. However, its provenance remains controversial. In this study, grain size analysis, and quartz grain surface microtextural and morphological observations, enabled comparison of the provenance of loess in the LRYR with those on the Loess Plateau in northern China. The results show that the grain size characteristics of the Xiashu loess do not follow the coarse-fine NW-SE trend in northern China, and the surface microtextures of the quartz grains in the Xiashu loess are distinctly different from those on the Loess Plateau in northern China, indicating that the loess deposits in the two regions have different provenances. The Gobi Desert in inland northwestern China are not considered as the primary provenance of the Xiashu loess. Instead, the adjacent floodplains in the LRYR, the alluvial plains of the Huai River and the Yellow River to the north during glacial periods are suggested as the dominant source materials for the Xiashu loess. Under the background of middle-Pleistocene climate transition (MPT), regional aridity and a strengthened east Asian winter monsoon (driven by global cooling and the rapid uplift of the Tibetan Plateau) were considered as the primary drivers for the development of the Xiashu loess. The sustained eolian loess accumulation represent a regional response of the northern subtropical area of southern China to the MPT global cooling event at around 0.9 Ma.

WOS:000653816200001; International audience; The East Asian marginal seas are among the most productive fisheries grounds. However, in recent decades they experienced massive proliferations of jellyfish that pose vast challenges for the management of harvested fish stocks. In the Korean Peninsula, the common bloom-formers Scyphozoan species Aurelia coerulea and Nemopilema nomurai are of major concern due to their detrimental effects on coastal socio-ecological systems. Here, we used pluriannual field observations spanning over 14 years to test the extent of climate influence on the interannual variability and bloom dynamics of A. coerulea and N. nomurai. To depict climate-jellyfish interactions we assessed partitioning effects, direct/indirect links, and the relative importance of hydroclimate forces on the variability of these species. We show that jellyfish interannual patterns and bloom dynamics are shaped by forces playing out at disparate scales. While abundance changes and earlier blooms of A. coerulea were driven by local environmental conditions, N. nomurai interannual patterns and bloom dynamics were linked with regional climate processes. Our results provide a synoptic picture of cascading effects from large scale climate to jellyfish dynamics in the Korean Peninsula that may affect fisheries sustainability due to the prominent detrimental impact these species have in the region.

Understanding the effects of aerosol on the regional climate change and environment requires long-term and high-resolution aerosol optical properties. An indirect method is employed to acquire aerosol optical depths (AODs) based on the atmospheric horizontal visibility and vapor pressure at 62 stations in South Central Hebei Plain (SCHP) from 1975 to 2016. Mann–Kendall tests are also applied to investigate the spatio-temporal variation of AODs in SCHP and their correlations with East Asian monsoon and secondary industry. Results indicate that large AOD values are concentrated in the southwest banding area centered in Shijiazhuang, Xingtai, and Handan, while low values in northeastern SCHP centered in Langfang and Cangzhou. Statistical analysis shows that the AODs significantly increased in summer and autumn over most regions of SCHP, except for some metropolises. Compared with the East Asian monsoon indexes (EAMI), the change in secondary industry output (SIO) is significantly correlated with variations of annual and seasonal mean AODs in SCHP from 1975 to 2016, with the highest correlation coefficient value at 0.63. The spatial distributions of correlations between EAMI/SIO and AODs indicate that AODs in winter are significantly correlated to the East Asian winter monsoon (EAWMI) over the eastern SCHP, while significant correlations between SIO and the mean AODs in summer, autumn, and year are all detected in the central–western SCHP. This research may help increase the accuracy of long-term aerosol prediction and improve air pollution control in the SCHP.

The variability of the winter monsoon is one of the key components of the Asian monsoon, significantly influencing paleoenvironmental evolution in East Asia. However, whether the winter or the summer monsoon is the dominated factor controlling sedimentary dynamics of the muddy areas of the continental shelves of the East China Sea is debated, due to lack of consistency between various winter monsoon proxies in previous studies. In this work, the sediments of the upper part of core ECS-DZ1 with several marine surface samples were studied in terms of sediment grain size and radiocarbon dating, and changes in sedimentary dynamics of the northern muddy area of the ECS over the past 5000 years were documented. The main findings are as follows: (1) regional sedimentary dynamics were low and did not significantly change since the middle Holocene, (2) coarse particles are the dominated component in the sediments, (3) a proxy can be derived to indicate changes in winter monsoon. Based on this reconstructed winter monsoon record, we found that this record was generally negatively correlated to the stalagmite-based summer monsoon variability over the past 3500 years, but positively correlated before that. Moreover, this record can be well correlated to changes in the Kuroshio Current and the Bond ice-rafting debris events in the North Atlantic on millennial timescales, inferring large-scale and common atmospheric dynamics across the Asian continent over the past 5000 years. Therefore, we concluded that the winter monsoon is the predominant factor controlling sedimentary dynamics in the northern part of the ECS and proposed that the contribution of coarse particles may be one of potential indices to identify the role of the winter and the summer monsoons in sedimentary evolution.

In this paper, the features and possible causes of extreme precipitation in the winter of 2019/2020 in China are investigated based on the observational station daily dataset provided by the China Meteorological Administration and the ECMWF ERA5 reanalysis dataset. Record-breaking precipitations are found in most areas of China in the winter of 2019/2020, particularly for the north of China. The magnitude of precipitation in south (north) of China in 2019/2020 increase 0.39 mm/day (0.15 mm/day), about 39.0% (105.5%) compared with the climatological mean. Moisture budget analysis shows that contributions of atmospheric circulation anomaly on horizontal moisture advection and total moisture flux convergence are primarily responsible for the positive anomalies of precipitation in China. Further analysis suggests that the weakened East Asian Trough and the anti-cyclone circulation anomaly over the Sea of Japan favor the transportation of low-level warm and humid airflow from the Northwest Pacific and the East China Sea to the north of China. Meanwhile, the westward movement of the Subtropical High and the Southern Branch Trough anomalies transport low-level warm and humid air from the Bay of Bengal and the South China Sea to south of China. The warm moist air flows northeastward from the East China Sea, Bay of Bengal and the South China Sea while the climatological cold wind flows southeastward, which causes the increase of local precipitation in the winter of 2019/2020. In consideration of the fact that stratospheric polar vortex anomaly has a process of downward propagation to the troposphere, it is of great significance to study the changes of the stratosphere and the relationships between stratosphere and troposphere.

Observations show that the East Asian winter monsoon (EAWM) experienced an interdecadal weakening in the mid-1980s. This is evident for all members of the EAWM system (i.e., East Asian trough, upper-tropospheric jet stream, and lower-tropospheric monsoon circulation). Here, we investigate the relative contributions of natural (volcanic aerosols and solar variability) and anthropogenic [greenhouse gases (GHGs) and anthropogenic aerosols] forcings to this interdecadal weakening using multiple coupled models within phase 5 of the Coupled Model Intercomparison Project (CMIP5). The results indicate that in the midtroposphere, the increased GHG concentrations play an important role in weakening the East Asian trough (EAT) by increasing the sea surface temperatures (SSTs) over the North Pacific. In the upper troposphere, natural external forcings contribute to the observed weakening of the meridional shear of the East Asian jet stream (EAJS) by regulating the meridional temperature gradient (MTG) over the East Asian region. In the lower troposphere, both anthropogenic and natural forcings can weaken the Siberian high during this period. Overall, based on the present analysis of the CMIP5 output, GHGs and natural forcings play key roles in shaping the observed interdecadal weakening of the EAWM during the mid-1980s. Additionally, contributions from internal variability cannot be neglected and require further investigation.

This study revisits the northern mode of East Asian winter monsoon (EAWM) variation and investigates its response to global warming based on the ERA dataset and outputs from phase 5 of the Coupled Model Intercomparison Project (CMIP5) models. Results show that the observed variation in East Asian surface air temperature (EAT) is tightly coupled with sea level pressure variation in the expanded Siberian high (SH) region during boreal winter. The first singular value decomposition (SVD) mode of the EAT and SH explains 95% of the squared covariance in observations from 1961 to 2005, which actually represents the northern mode of EAWM variation. Meanwhile, the first SVD mode of the EAT and SH is verified to be equivalent to the first empirical orthogonal function mode (EOF1) of the EAT and SH, respectively. Since the leading mode of the temperature variation is significantly influenced by radiative forcing in a rapidly warming climate, for reliable projection of long-term changes in the northern mode of the EAWM, we further employ the EOF1 mode of the SH to represent the northern mode of EAWM variation. The models can well reproduce this coupling between the EAT and SH in historical simulations. Meanwhile, a robust weakening of the northern mode of the EAWM is found in the RCP4.5 scenario, and with stronger warming in the RCP8.5 scenario, the weakening of the EAWM is more pronounced. It is found that the weakening of the northern mode of the EAWM can contribute 6.7% and 9.4% of the warming trend in northern East Asian temperature under the RCP4.5 and RCP8.5 scenarios, respectively.

The Indonesian throughflow (ITF) impacts heat and buoyancy transport from the Pacific Ocean to the Indian Ocean, influencing air‐sea heat exchange and Indo‐Pacific climate. Nearly 80% of the total 15 sverdrups (1 Sv = 106 m3/s) of ITF water moves through the Makassar Strait in the western Indonesian seas, with ~20% of total ITF transport subsequently entering the Indian Ocean through the Lombok Strait. During the East Asian winter monsoon (EAWM), buoyant South China Sea (SCS) waters obstruct southward surface ITF transport in the Makassar Strait, likely impacting surface variability throughout the Lombok Strait. Here we present two subannually resolved, multicentury records of coral‐reconstructed sea surface salinity (SSS) from the northern (110 years) and southern Lombok Strait (193 years). Differences in boreal winter (January–March) SSS variability between the two sites suggest the influence of multiple source waters. Instrumental and reconstructed temperature‐salinity (T‐S) relationships indicate that SCS surface waters dominate the northern Lombok Strait, while Indian Ocean surface waters instead dominate the southern Lombok Strait before 1960. These dissimilarities are likely due to changes in monsoon‐driven surface water advection. At the northern site, the EAWM consistently influences SSS variability. The EAWM influence at the southern site, however, reverses in direction (inverse to direct) coincidentally with a transition from a positive (strong) to negative (weak) EAWM state in 1960. Our records collectively reveal that changes in the strength and state of the EAWM impact Lombok Strait surface water circulation, likely interacting with southward ITF transport and thus Indo‐Pacific climate. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Published version

We examined the correlations between winter aerosol optical depth (AOD) in North China (NC) and three synoptic-scale meteorological indices from 2001 to 2016, including the Siberian High intensity (SHI), East Asian Winter Monsoon intensity (EAWMI), and the Siberian High Position index (SHPI). To separate the influences from meteorology and emissions, NC AOD was detrended by subtracting a linear increasing trend from 2001 to 2013 and a decreasing trend from 2014 to 2016, in correspondence with reported changes in Chinese anthropogenic emissions during the same period. The SHPI explains 37% of the variability in the detrended NC AOD and 83% of the high SHPI winters correspond to high AOD. By contrast, the SHI and EAWMI show little correlation with the observed AOD variability. To project the SHPI in the future climate, we used the ensemble of six global circulation models (GCMs) which were found capable of reproducing the climatic spatial distribution and the longitudinal variability of the Siberian High from 1956 to 2005. The ensemble results show that the frequency of high SHPI winters and consequently more polluted conditions would increase by 29%, 61%, and 100% under RCP2.6, RCP4.5 and RCP8.5 until 2099. There are 11 out of the 25 GCMs examined here that project the possibility of high SHPI conditions to increase under RCP8.5. This indicates changes in the Siberian High position induced by increasing global greenhouse gas (GHG) emissions can lead to more winter pollution in North China in the future.

Due to the negligence of the author, the third affiliation and address “Institute of Meteorology and Oceanography, The Army Engineering University of PLA, Nanjing 211101, China” in the originally published article version was not correct, and should be changed to “Institute of Meteorology & Oceanography, National University of Defense Technology, Nanjing 211101, China”, hereby certify.

Changes in East Asian summer and winter monsoon intensity have played a pivotal role in the prosperity and decline of society in the past, and will be important for future climate scenarios. However, the phasing of changes in the intensity of East Asian summer and winter monsoons on millennial and centennial timescales during the Holocene is unclear, limiting our ability to understand the factors driving past and future changes in the monsoon system. Here, we present a high resolution (up to multidecadal) loess record for the last 3.3 ka from the southern Chinese Loess Plateau that clearly demonstrates the relationship between changes in the intensity of the East Asian summer and winter monsoons, particularly at multicentennial scales. At multimillennial scales, the East Asian summer monsoon shows a steady weakening, while the East Asian winter monsoon intensifies continuously. At multicentennial scales, a prominent ∼700–800 yr cycle in the East Asian summer and winter monsoon intensity is observed, and here too the two monsoons are anti-phase. We conclude that multimillennial changes are driven by Northern Hemisphere summer insolation, while multicentennial changes can be correlated with solar activity and changing strength of the Atlantic meridional overturning circulation.

This study evaluates the relative importance of diabatic heating and intraseasonal disturbances with regard to the variabilities of the East Asian jet stream (EAJS) associated with the East Asian winter monsoon (EAWM). First, strong and weak monsoon years are selected based on the EAWM index of Jhun and Lee, which is highly correlated with the monsoon northerlies between the Eurasian continent and the Pacific. The EAJS is stronger and narrower in strong monsoon years and weaker and wider in weak monsoon years. Model experiments were performed to investigate the atmospheric response to the diabatic heating and the eddy–mean flow feedback from the intraseasonal disturbances. The diabatic heating is closely related to the convective activities. The intraseasonal disturbances include high-frequency components with periods of 3–10 days and low-frequency components with periods of 10–90 days. The model results indicate that the diabatic heating plays a major role maintaining the stronger and weaker EAJS in the strong and weak monsoon years, respectively, whereas the impacts of the eddy feedback are relatively small.

The impacts of the eastern-Pacific (EP) and central-Pacific (CP) El Nino-Southern Oscillation (ENSO) on the southern China wintertime rainfall (SCWR) have been investigated. Results show that wintertime rainfall over most stations in southern China is enhanced (suppressed) during the EP (CP) El Nino, which are attributed to different atmospheric responses in the western North Pacific (WNP) and South China Sea (SCS) during two types of ENSO. When EP El Nino occurs, an anomalous low-level anticyclone is present over WNP/the Philippines region, resulting in stronger-than-normal southwesterlies over SCS. Such a wind branch acts to suppress East Asian winter monsoon (EAWM) and enhance moisture supply, implying surplus SCWR. During CP El Nino, however, anomalous sinking and low-level anticyclonic flow are found to cover a broad region in SCS. These circulation features are associated with moisture divergence over the northern part of SCS and suppressed SCWR. General circulation model experiments have also been conducted to study influence of various tropical sea surface temperature (SST) patterns on the EAWM atmospheric circulation. For EP El Nino, formation of anomalous low-level WNP anticyclone is jointly attributed to positive/negative SST anomalies (SSTA) over the central-to-eastern/ western equatorial Pacific. However, both positive and negative CP Nino-related-SSTA, located respectively over the central Pacific and WNP/SCS, offset each other and contribute a weak but broad-scale anticyclone centered at SCS. These results suggest that, besides the vital role of SST warming, SST cooling over SCS/WNP during two types of El Nino should be considered carefully for understanding the El Nino-EAWM relationship.

This study investigates the transition from East Asian winter monsoon (EAWM) to following summer monsoon (EASM) under two types of El Nino and La Nina events. A robust out-of-phase transition from weak EAWM to strong EASM is related to El Nino events, which is more distinct in eastern Pacific (EP) El Nino than that in central Pacific (CP) El Nino due to the stronger and wider western North Pacific (WNP) anticyclone (WNPAC) as a persistent atmospheric bridge. The WNPAC differences result from the combined impacts of the warming over northern Indian Ocean (NIO) remotely, the dipolar sea surface temperature (SST) anomalies and the anomalous sinking motion over WNP locally. In terms of La Nina, the out-of-phase strong EAWM to weak EASM transition exists only for CP La Nina. Moreover, this connection is weaker compared to that for El Nino events because of a weaker WNP cyclone (WNPC). Conversely, when EP La Nina occurs, an in-phase transition is detected with a strong EAWM evolving into a strong EASM due to the emergence of WNPAC in summer. For CP and EP La Nina, the cooling SST anomalies over NIO and WNP play opposite roles in affecting WNP summertime circulation anomalies. Observational and model results suggest that the WNPC (WNPAC) is dominated by remote (local) cooling in NIO (WNP) in the summer following CP (EP) La Nina. In addition, the local rising (sinking) flow also contributes to the WNPC (WNPAC) associated with CP (EP) La Nina.

The influence of human nuclear activities on environmental radioactivity is not well known at low latitude region that are distant from nuclear tests sites and nuclear facilities. A sediment core collected from Taal Lake in the central Philippines was analyzed for 129I and 127I to investigate this influence in a low-latitude terrestrial system. A baseline of 129I/127I atomic ratios was established at (2.04–5.14) × 10−12 in the pre-nuclear era in this region. Controlled by the northeasterly equatorial trade winds, increased 129I/127I ratios of (20.1–69.3) × 10−12 suggest that atmospheric nuclear weapons tests at the Pacific Proving Grounds in the central Pacific Ocean was the major source of 129I in the sediment during 1956–1962. The 129I/129I ratios, up to 157.5 × 10−12 after 1964, indicate a strong influence by European nuclear fuel reprocessing plants. The East Asian Winter Monsoon is found to be the dominant driving force in the atmospheric dispersion of radioactive iodine (129I) from the European nuclear fuel reprocessing plants to Southeast Asia, which is also important for dispersion of other airborne pollutants from the middle-high, to low latitude regions. A significant 129I/127I peak at 42.8 cm in the Taal Lake core appears to be the signal of the Chernobyl accident in 1986. In addition, volcanic activities are reflected in the iodine isotope profiles in the sediment core, suggesting the potential of using iodine isotopes as an indicator of volcanic eruptions.

The East Asian winter monsoon (EAWM) plays a significant role in the Asian climate system. However, the scarcity of direct high-resolution records, especially those covering recent centuries, limits our understanding of monsoonal dynamics. Here we present a reconstruction of annual EAWM strength over the past century and a half using a Porites coral from Yongxing Island in the northern South China Sea (SCS), where the variations in the rare earth element (REE) parameters in surface seawater are dominantly controlled by the input of aeolian dust. Our record indicates that the EAWM strength weakly increased overall during the latter half of the nineteenth century but decreased during the twentieth century, especially after ~1950 Common Era. Additionally, during the past century and a half, the relationship between the EAWM and the East Asian summer monsoon, as recorded in speleothems, varied temporally and depended on the strength of the EAWM. Our findings suggest that the REE proxy of corals from the offshore SCS can be applied as an excellent indicator of the winter monsoon strength.

Using ensemble empirical mode decomposition (EEMD) for detecting the interdecadal changes in the East Asian winter monsoon (EAWM), this study identifies that the intensity of the EAWM experienced remarkable transition around mid-1980s and late 2000s: a strong period (P1, 1960–1986), a weak period (P2, 1987–2007), and a strong period (P3, 2008–2015). A distinctive cold (warm) surface temperature anomaly is found over the Eurasian continent including East Asia, and cold (warm) sea surface temperature (SST) anomalies are present over the North Pacific (NP) during P1 (P2). In contrast with P1, the EAWM is characterized by a large temperature difference between Eurasian continent and NP, and a negative Pacific Decadal Oscillation (PDO)-like SST anomaly pattern is found over the NP during P3. During three periods, the Siberian high (SH) plays an important role in deciding the intensity of the EAWM. In addition, the EAWM exists under the influence of an enhanced atmospheric circulation associated with a positive North Pacific Oscillation (NPO) and a negative PDO during P2 and P3, respectively. Accordingly, to recognize the relative importance of each combined effect which it differs for times, the combined effect of SH and NPO (SH and PDO) variability on the weakening (strengthening) EAWM is explored during P1 and P2 (P2 and P3). Consequently, while the atmospheric variabilities of SH and NPO bring about the weakening of EAWM after the mid-1980s, the SST variability related to PDO with the SH variabilty is involved in the strengthening of EAWM in recent decade.

This study analysed the time series of tropical cyclone (TC) frequency during October–December (OND) for 32 years (1980–2011). There was a strong decreasing trend of TCs until recently, and the TC sharply decreased from 1996 after the statistical change-point analysis was applied to this time series. To investigate the cause of such recent decrease in TC genesis frequency, the differences (TC activity and its relation to large-scale environments, and others) between the mean of the period from 1996 to 2011 and the mean of the period from 1980 to 1995 were analysed. TCs during the period 1996–2011 mainly occurred in the western region of tropical western North Pacific (TWNP), whereas during the 1980–1995 period they mainly occurred in the eastern region of TWNP. In the analysis of differences periods in the 850 hPa and 500 hPa stream flows between the two periods, an anomalous huge anticyclone existed from the north Pacific to the TWNP, and an anomalous huge cyclone existed to the west of 125°E including the East Asian continent. In other words, this is a typical low-west-high-east pressure system that appears in East Asia during summer, and this anomalous pressure system pattern caused the low TC genesis frequency during the 1996–2011 period. The low-west-high-east anomalous pressure system pattern which has been strengthened recently in East Asia suggests that the East Asian winter monsoon (EAWM) has weakened during the 1996–2011 period. As a result, the amount of snow depth decreased in many areas of the East Asian continent except for the North China and the ground heat net flux also increased in many areas. This weakening of the EAWM strengthened the anomalous huge anticyclone in the TWNP as well as in the central North Pacific, which caused the low TC genesis frequency during the OND in recent years.

We used two 150-year pre-industrial simulations of the Community Earth System Model (CESM), one with interactive dust and the other with prescribed dust, to quantify the impacts of changes in wind during East Asian Winter Monsoon (EAWM) season on dust emissions, and the resulting consequences for interannual variations of temperature and precipitation over East Asia. The simulated December-January-February dust column burden and dust optical depth are lower over northern China in the strongest EAWM years than those of the weakest years by 38.3% and 37.2%, respectively. The decrease in dust over the dust source regions and the downwind region leads to an increase in direct radiative forcing (RF) at the surface by up to 1.5 Wm-2. The effects of EAWM-related variations in surface winds, precipitation and their effects on dust emissions and wet removal contribute 67% to the total dust-induced variations of direct RF at the surface and partly offset the cooling that occurs with the EAWM strengthening by heating the surface. The variations of surface air temperature induced by the changes in wind and dust emissions between the strongest and weakest EAWM years (strongest minus weakest) decrease by 0.4-0.6 K from eastern coastal China to Japan, which weakens the impact of EAWM on surface air temperature by 3–18% in these regions. The warming results from the combined effects of changes in direct RF, turbulent heat flux at the surface, and northwesterly wind anomalies that bring cold and dry air from Siberia to these regions. Over eastern coastal China, the variations of large-scale precipitation induced by the feedback of EAWM-related changes in wind on dust emissions decrease by 10-30% in winter because of the reducing changes in surface air temperature and the anomalous circulation.

While mean grain size of sensitive component in muddy sediments from Chinese coastal seas was widely used as a proxy for reconstruction of the East Asian winter monsoon (EAWM) strength, many intractable problems still remain concerning the discrepancies in different studies. This paper provides a comprehensive overview of recent researches on the reconstruction of Holocene EAWM strength using sensitive grain size (SGS) in muddy sediments from the Chinese coastal seas. In the present study, 15 time-series of SGS in sediments from six mud areas are included. These records are summarized and compared during the last 8000 years, 3000 years and 150 years, respectively. The results show that trends of SGS time-series are inconsistent at millennial, multi-centennial and decadal time scales. The inconsistencies could be partly caused by age uncertainties and chosen SGSs. More important, grain size characteristics in sediments from some mud areas could be influenced by factors other than coastal currents driven by EAWM, such as sedimentary environments, riverine runoff and storms. Thus SGS of muddy sediments should be used with caution when reconstructing winter monsoon strength, especially those in the northern Yellow Sea and near the Yangtze River estuary.

This study investigates the individual effects of the East Atlantic/West Russia (EATL/WRUS) and Western Pacific (WP) teleconnection patterns and their combined effect on the East Asian winter monsoon (EAWM). The contributions of the respective EATL/WRUS and WP teleconnection patterns to the EAWM are revealed by removing the dependence on the Arctic Oscillation (AO) and the El Nino-Southern Oscillation (ENSO) using a linear regression, which are named as N_EATL/WRUS and N_WP, respectively. This is because the EATL/WRUS (WP) is closely linked to the Arctic (tropics) region. A significant increase (decrease) in temperature over East Asia (EA) corresponding to a weak (strong) EAWM is associated with the N_EATL/WRUS and N_WP teleconnection patterns during the positive (negative) phases. In order to examine impacts of these two teleconnections on the EAWM, three types of effects are reconstructed on the basis of ± 0.5 standard deviation: 1) Combined effect, 2) N_EATL/WRUS effect, and 3) N_WP effect. The positive N_EATL/WRUS teleconnection induces to a weakened Siberian High and a shallow EA trough at the mid-troposphere through wave propagation, leading to the weak EAWM. During the positive N_WP pattern, warm air from the tropics flows toward the EA along western flank of an anomalous anticyclone over the North Pacific that is relevant to the meridional shift of the Aleutian Low. When the two mid-latitude teleconnections have the in-phase combination, the increase in temperature over EA appears to be more pronounced than the individual effects by transporting warm air from tropics via strong southeasterly wind anomalies induced by anomalous zonal pressure gradient between the Siberian High and Aleutian Low. Therefore, the impact of the mid-latitude teleconnections on the EAWM becomes robust and linearly superimposed, unlike a nonlinear in-phase combined effect of the AO and ENSO.

Using long-term observational data and numerical model experiments, this study found that the Atlantic multidecadal oscillation (AMO) affects the influence of ENSO-like sea surface temperature anomalies (SSTAs, which contain the variability of both El Niño–Southern Oscillation and Pacific decadal oscillation) on the interannual change in the East Asian winter monsoon (EAWM). In the observations, the out-of-phase relationship between the variations in ENSO and the EAWM was significantly intensified when the AMO and ENSO-like SSTAs were in phase. Warmer-than-normal winters occurred across East Asia when the ENSO-like SSTAs and AMO were positively in phase, with a significantly weakened Siberian high and anomalous anticyclones over the western North Pacific. The opposite patterns occurred under negative in-phase conditions. In contrast, when the ENSO-like and AMO SSTAs were out of phase, the anomalies related to the EAWM tended to exhibit relatively weaker features. Numerical model experiments confirmed these observational results. When the models were perturbed with warm ENSO-like SSTAs and warm AMO SSTAs, the atmosphere showed a weakened Siberian high, strong anticyclonic anomalies over the Philippine Sea, a weakened East Asian trough, and dominant positive temperature anomalies over East Asia, implying a weaker EAWM. Reverse responses to negative in-phase temperature anomalies were observed. However, the atmospheric signals that responded to the out-of-phase conditions were less robust. This phenomenon may be attributed to the superposition of the interannual variability of the EAWM caused by ENSO-like SSTAs upon the influence of AMO on background Eurasian climate and the Walker circulation response to the heating source provided by the AMO, which induced changes in ENSO-like variability through the surface wind anomalies and modulated the anomalous anticyclone/cyclone over the Philippine Sea in warm–cold ENSO-like events.

Large intraseasonal rainfall variations are identified over the southern South China Sea (SSCS), tropical southeastern Indian Ocean (SEIO), and east coast of the Philippines (EPHI) in boreal winter. The present study contrasts origins and propagations and investigates interrelations of intraseasonal rainfall variations on the 10–20- and 30–60-day time scales in these regions. Different origins are identified for intraseasonal rainfall anomalies over the SSCS, SEIO, and EPHI on both time scales. On the 10–20-day time scale, strong northerly or northeasterly wind anomalies related to the East Asian winter monsoon (EAWM) play a major role in intraseasonal rainfall variations over the SSCS and EPHI. On the 30–60-day time scale, both the intraseasonal signal from the tropical Indian Ocean and the EAWM-related wind anomalies contribute to intraseasonal rainfall variations over the SSCS, whereas the EAWM-related wind anomalies have a major contribution to the intraseasonal rainfall variations over the EPHI. No relation is detected between the intraseasonal rainfall variations over the SEIO and the EAWM on both the 10–20-day and 30–60-day time scales. The anomalies associated with intraseasonal rainfall variations over the SSCS and EPHI propagate northwestward and northeastward, respectively, on the 10–20- and 30–60-day time scales. The intraseasonal rainfall anomalies display northwestward and northward propagation over the Bay of Bengal, respectively, on the 10–20- and 30–60-day time scales.

The relationship between the East Asian winter monsoon (EAWM) and East Asian summer monsoon (EASM) during the Holocene is complicated and remains controversial. In this study, analysis of grain size and benthic foraminiferal oxygen isotope, as well as accelerator mass spectrometry 14C dating was performed on a sediment core retrieved from the newly revealed muddy deposit on the northern South China Sea continental shelf. The history of the EAWM and EASM were reconstructed for the last 8200 a BP. Further analysis in conjunction with previously published paleo-climate proxies revealed that the relationship between the EAWM and EASM during the Holocene is more complex than a simple and strict anti-phase one-both negative and positive correlations were identified. The EAWM and EASM are negatively correlated around 7500, 4800, 4200, 3200, and 300 a BP (cooling periods), while positively correlated around 7100, 3700, and 2100 a BP (warm periods). In particular, both the EAWM and EASM intensified during the three positive correlation periods. However, we also found that the relationship between these two sub-monsoons is anti-phase during the final phase of particularly hot periods like Holocene Optimum and Medieval warm period. The possible impact from variations of solar irradiance on the relationship between the EAWM and EASM was also discussed.

Nine potential vorticity (PV) regimes over East Asia are identified by applying a Self-Organizing Map and Hierarchical Ascendant Classification regime analysis to the daily PV reanalysis fields on the 300K isentropic surface for December-March 1948–2014. According to the surface temperature anomalies over East Asia, these nine regimes are further classified into three classes, i.e., cold class (three regimes), warm class (four regimes), and neutral class (two regimes). The PV-based East Asian winter monsoon index (EAWMI) is used to study the relationship between PV distributions and the temperature anomalies. The magnitude of cold (warm) anomalies over the land areas of East Asia increases (decreases) quasi-linearly with the EAWMI. Regression analysis reveals that cold temperature anomalies preferentially occur when the EAWMI exceeds a threshold at ∼0.2PVU (where 1PVU≡10−6 m2 Kkg−1 s−1). PV inversion uncovers the mechanisms behind the relationships between the PV regimes and surface temperature anomalies, and reveals that cold (warm) PV regimes are associated with significant warming (cooling) in the upper troposphere and lower stratosphere. On average, cold regimes have longer durations than warm regimes. Interclass transition probabilities are much higher for paths from warm/neutral regimes to cold regimes than for paths from cold regimes to warm/neutral regimes. Besides, intraclass transitions are rare within the warm or neutral regimes. The PV regime analysis provides insight into the causes of severe cold spells over East Asia, with blocking circulation patterns identified as the primary factor in initiating and maintaining these cold spells.

This study investigates the variations and feedback attributions of changes in surface temperature between strong and weak East Asian winter monsoons. The variations of winter-mean surface air temperature are dominated by two distinct principal modes that account for 70.9% of the total variance. The first mode features high correlation with the high-latitude atmospheric circulation, including a correlation coefficient of −0.53 with the Arctic Oscillation in January, and the second mode is significantly linked to El Niño–Southern Oscillation, with a correlation coefficient of −0.37. The surface temperature anomalies of each mode are decomposed into partial temperature anomalies resulting from radiative and nonradiative feedback processes by applying a coupled climate feedback–response analysis method to quantify contributions from thermodynamic and dynamic processes. Results indicate that the surface cooling associated with both modes is mainly attributed to the nonradiative feedback processes of atmospheric dynamics and surface sensible heating and to the radiative feedback processes of water vapor and clouds. The first mode exhibits a deep barotropic anomalous high that weakens the high-latitude westerly jet stream but strengthens the midlatitude westerly jet stream. This circulation feature traps cold and dry air over northern East Asia. For the second mode, the ocean and land heat storage processes induce a large thermal gradient over eastern China and the northwestern Pacific, resulting in a large pressure gradient. Northerly anomalies further reinforce the pressure gradient, which favors cold air intruding southward into the tropics.

The East Asian winter monsoon (EAWM) is greatly influenced by many factors that can be classified as anthropogenic forcing and natural forcing. Here we explore the contribution of anthropogenic influence to the change in the EAWM over the past decades. Under all forcings observed during 1960–2013 (All-Hist run), the atmospheric general circulation model is able to reproduce the climatology and variability of the EAWM-related surface air temperature and 500 hPa geopotential height and shows a statistically significant decreasing EAWM intensity with a trend coefficient of ∼-0.04 yr−1, which is close to the observed trend. By contrast, the simulation, which is driven by the same forcing as the All-Hist run but with the anthropogenic contribution to them removed, shows no decreasing trend in the EAWM intensity. By comparing the simulations under two different forcing scenarios, we further reveal that the responses of the EAWM to the anthropogenic forcing include a rise of 0.6∘ in surface air temperature over East Asia as well as weakening of the East Asian trough, which may result from the poleward expansion and intensification of the East Asian jet forced by the change in temperature gradient in the troposphere. Additionally, compared with the simulation without anthropogenic forcing, the frequency of strong (weak) EAWM occurrence is reduced (increased) by 45 % (from 0 to 10/7). These results indicate that the weakening of the EAWM during 1960–2013 may be mainly attributed to the anthropogenic influence.