East Asian Winter Monsoon Variability Research Articles

A multiproxy reconstruction of Asian winter monsoon variability since the last glacial from southeast offshore Hainan Island, South China Sea

The evolution of East Asian winter monsoon (EAWM) in tropical oceans has been a key issue in the climatic coupling between high- and low-latitudes. This study aims to investigate the EAWM variability using multiproxy of sediment core XB19S40 in the southeast offshore of Hainan Island, South China Sea. Alkenone derived sea surface temperature (SST), sediment grain size, and elemental ratios show consistent changes over the last 20.7 ka. There were synchronous abrupt changes in the SST, Zr/Rb, K/Ti, and End-members (EMs) during the Bølling-Allerød warming period, Younger Dryas and 8.2 ka cooling events. The Zr/Rb and EM2 (18.7–84.6 μm, 40.1 μm) changes reflect the EAWM and are highly coincident with records in high latitudes. These changes suggest that the EAWM gradually weakened from the last glacial maximum to early Holocene, experienced minor strengthening in the late Holocene but has diminished since 1 ka. In contrast, the indicators K/Ti and EM1 (0.2–18.7 μm, 9.9 μm) suggest that the East Asian summer monsoon is in the opposite phase. Spectral analysis demonstrates that the intensity of East Asian monsoons in the SCS were mainly affected by solar activity on a centennial-scale. The results of this study provide new insight into the complexity of the EAWM system and emphasize the importance of understanding multiple components of the climate system.

Natural and anthropogenic forcing on the fate of sedimentary organic matter in the South Yellow Sea during the Holocene

Long-term organic matter (OM) burial in the ocean is essential to the global carbon cycle. Mud deposits, such as South Yellow Sea mud deposit (SYSMD) located in the central South Yellow Sea (SYS), are ideal for the study of long-term OM burial. A sediment core YS-A from the SYSMD was analyzed for lignin phenols and bulk OM properties to reveal the driving forces of sedimentary OM (SOM) fate during the Holocene. SOM burial was found to be dominantly influenced by sea level rise and increased East Asian summer monsoon during 11.0–7.0 ka BP. During 7.0–1.0 ka BP, the fate of SOM was controlled by El Niño Southern Oscillation on the millennial time scale, and correlated with East Asian winter monsoon variability on the centennial time scale. Remarkably, anthropogenic perturbation has gradually overwhelmed long-term climate control on the fate of SOM since 1.0 ka BP, and this phenomenon became more evident after 0.4 ka BP.

Summer Arctic Atmospheric Circulation and Its Association With the Ensuing East Asian Winter Monsoon Variability

AbstractThe impact of autumn Arctic sea ice reduction on the winter climate in Eurasia has been widely studied, but the role of the atmospheric circulation of the preceding summer has been mostly neglected. This study investigates a linkage between the summer Arctic circulation anomaly and the ensuing East Asian Winter Monsoon (EAWM) variability. The Arctic circulation anomaly, characterized by an anomalous anti‐cyclone occupying the Arctic Ocean and its marginal seas, can strongly melt Arctic sea ice in the Kara Sea‐Laptev Sea‐East Siberian Sea‐Chukchi Sea‐Beaufort Sea through dynamic and thermodynamic processes. The combination of the summer anti‐cyclone (cyclone) anomaly and light (heavy) autumn sea ice leads to an enhanced (weakened) EAWM. By introducing the coupling relationship between summer circulation and autumn sea ice into numerical experiments, the Community Atmospheric Model version 4 model has a good capability for capturing EAWM variability. Nevertheless, the dominant features of EAWM variability cannot be reproduced when the autumn sea ice mismatches the preceding summer circulation in the model. Therefore, the preceding summer circulation may modulate the impact of sea ice on Eurasia to some extent, which may increase uncertainties in the impact of Arctic sea ice loss on winter atmospheric circulation variability.

Centennial-scale East Asian winter monsoon variability within the Younger Dryas

The Younger Dryas (YD) is recognized as a millennial-scale cold climate event that occurred during the last deglaciation in the Northern Hemisphere. Modeling and geological evidences reveal that the YD period was punctuated by multiple rapid changes at interdecadal to centennial timescales. However, characteristics and mechanism of abrupt climate variability within the YD in its most pronounced winter interval remain poorly constrained. Here, we present two high-resolution loess grain-size time series from the western Chinese Loess Plateau (CLP) to address centennial-scale East Asian winter monsoon (EAWM) variability during this phenomenal cooling event. The mean grain size results reveal two cold intervals of the Heinrich event 1 and YD during the last deglaciation, corresponding well to climate changes from regional and global context. More importantly, the mean grain size results demonstrate a persistent centennial-scale EAWM variability within the YD. We propose that this was caused by the North Atlantic sea ice variation via fast atmospheric processes between the subpolar and mid-latitude regions. We also observed a marked decrease in magnitudes of centennial-scale EAWM variability around the mid-YD. Such a mid-YD shift is closely related to a northward shift of the atmospheric polar front and sea ice retreat induced by the resumption of the Atlantic meridional overturning circulation (AMOC). Our results suggest that the AMOC-induced sea ice change in the North Atlantic plays a more dominant role than the AMOC itself in transmitting abrupt climate signals over the Northern Hemisphere.

Simulations of the East Asian Winter Monsoon on Subseasonal to Seasonal Time Scales Using the Model for Prediction Across Scales

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.

A tale of shifting relations: East Asian summer and winter monsoon variability during the Holocene

Understanding the dynamics between the East Asian summer (EASM) and winter monsoon (EAWM) is needed to predict their variability under future global warming scenarios. Here, we investigate the relationship between EASM and EAWM as well as the mechanisms driving their variability during the last 10,000 years by stacking marine and terrestrial (non-speleothem) proxy records from the East Asian realm. This provides a regional and proxy independent signal for both monsoonal systems. The respective signal was subsequently analysed using a linear regression model. We find that the phase relationship between EASM and EAWM is not time-constant and significantly depends on orbital configuration changes. In addition, changes in the Atlantic Meridional Overturning circulation, Arctic sea-ice coverage, El Niño-Southern Oscillation and Sun Spot numbers contributed to millennial scale changes in the EASM and EAWM during the Holocene. We also argue that the bulk signal of monsoonal activity captured by the stacked non-speleothem proxy records supports the previously argued bias of speleothem climatic archives to moisture source changes and/or seasonality.

Stalagmite evidence for East Asian winter monsoon variability and 18O-depleted surface water in the Japan Sea during the last glacial period

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.

Spatial variation of East Asian winter monsoon evolution between northern and southern China since the last glacial maximum

AbstractThe East Asian winter monsoon (EAWM) is one of the most dynamic components of the global climate system. Although poorly understood, knowledge of long-term spatial differences in EAWM variability during the glacial–interglacial cycles is important for understanding the dynamic processes of the EAWM. We reconstructed the spatiotemporal characteristics of the EAWM since the last glacial maximum (LGM) using a comparison of proxy records and long-term transient simulations. A loess grain-size record from northern China (a sensitive EAWM proxy) and the sea surface temperature gradient of an EAWM index in sediments of the southern South China Sea were compared. The data–model comparison indicates pronounced spatial differences in EAWM evolution, with a weakened EAWM since the LGM in northern China but a strengthened EAWM from the LGM to the early Holocene, followed by a weakening trend, in southern China. The model results suggest that variations in the EAWM in northern China were driven mainly by changes in atmospheric carbon dioxide (CO2) concentration and Northern Hemisphere ice sheets, whereas orbital insolation and ice sheets were important drivers in southern China. We propose that the relative importance of insolation, ice sheets, and atmospheric CO2for EAWM evolution varied spatially within East Asia.

Diagnostic Metrics for Evaluating Model Simulations of the East Asian Monsoon

AbstractThe distinctive monsoon climate over East Asia, which is affected by the vast Eurasian continent and Pacific Ocean basin and the high-altitude Tibetan Plateau, provides arguably the best testbed for evaluating the competence of Earth system climate models. Here, a set of diagnostic metrics, consisting of 14 items and 7 variables, is specifically developed. This physically intuitive set of metrics focuses on the essential features of the East Asian summer monsoon (EASM) and East Asian winter monsoon (EAWM), and includes fields that depict the climatology, the major modes of variability, and unique characteristics of the EASM. The metrics are applied to multimodel historical simulations derived from 20 models that participated in phases 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5, respectively), along with the newly developed Nanjing University of Information Science and Technology Earth System Model, version 3. The CMIP5 models show significant improvements over the CMIP3 models in terms of the simulated East Asian monsoon circulation systems on a regional scale, major modes of EAWM variability, the monsoon domain and precipitation intensity, and teleconnection associated with the heat source over the Philippine Sea. Clear deficiencies persist from CMIP3 to CMIP5 with respect to capturing the major modes of EASM variability, as well as the relationship between the EASM and ENSO during El Niño developing and decay phases. The possible origins that affect models’ performance are also discussed. The metrics provide a tool for evaluating the performance of Earth system climate models, and facilitating the assessment of past and projected future changes of the East Asian monsoon.

Impacts of Summer North Atlantic Sea Surface Temperature Anomalies on the East Asian Winter Monsoon Variability

Abstract 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.

Change in Relationship between the East Asian Winter Monsoon and the East Asian Jet Stream during the 1998–99 Regime Shift

Abstract A composite analysis was conducted on the reanalysis dataset for 1979–2016, along with an idealized model experiment to show that the relationship between the East Asian jet stream (EAJS) and the East Asian winter monsoon (EAWM) is nonstationary. The relationship between EAWM and the EAJS weakened during the late 1990s. This decadal change in the EAJS–EAWM relationship was mainly due to a change in the secondary circulation across the EAJS between two contrasting periods, induced by the northward shift of the EAJS. A possible mechanism associated with the decadal change in meridional displacement of the EAJS is proposed. The enhanced convective activity in the western tropical Pacific after the late 1990s results in stronger Hadley circulation that could have contributed to the northward displacement of the Hadley circulation boundary latitude. Subsequently, this leads to the northward shift of the EAJS. Therefore, it is necessary to define a new EAJS index to account for the EAWM variability based on the change in the oceanic and atmospheric mean state across the late 1990s.

Individual and Combined Impacts of Two Eurasian Wave Trains on Intraseasonal East Asian Winter Monsoon Variability

AbstractThe present study investigates the intraseasonal wind variations over East Asia during boreal winter. It is shown that the wind variations less than 30 days are the main component of total intraseasonal signal. The intraseasonal variations in this time period are associated with two distinctive wave trains over Eurasia starting from the North Atlantic Ocean. One wave train propagates along the polar front jet eastward over Europe and Siberia and then southeastward after passing the Lake Baikal. The other wave train propagates along the subtropical jet southeastward through the Mediterranean region and the Arabian Peninsula to north India and then eastward to southern China. The East Asian wind and temperature anomalies are determined by the combination of the two wave trains. An anomalous cyclone forms over East Asia with large extent and intensity when the two wave trains work coherently, resulting in strong lower‐level northerly wind anomalies with a large meridional extent. More cold air is transported southward from high latitudes by anomalous northerly winds, causing widespread and large temperature decrease in East Asia. When only a single wave train exists, lower‐level wind and temperature anomalies are reduced. When there is a destructive interference of the two wave trains, the lower‐level wind and temperature anomalies are weak in East Asia. Observational analyses and barotropic model experiments indicate that the formation of the two wave trains may be related to the combination of disturbances at different locations over the North Atlantic Ocean.

Historical Variation in the Distribution of Trace and Major Elements in a Poor Fen of Fenghuang Mountain, NE China

Ombrotrophic bogs are widely used to reconstruct the history of atmospheric metal deposition. Minerotrophic fens are potential archives as well but not much attention has been paid to them. This study examined the accumulation of major and trace elements in a poor fen of Fenghuang Mountain, NE China. Peat cores were dated by 210Pb and 137Cs techniques and elemental analyses were conducted after a two-step sequential digestion with HCl. Results suggest no significant pollution for other trace metals but Pb in Fenghuang Mountain area. Atmospheric soil dust flux (ASD) was calculated from the Ti content in the peat, and its decreasing trend over the last 60 years agrees with the East Asian winter monsoon (EAWM) shift, which suggests that ASD could be a potential climatic proxy for the EAWM variability in the region.

Paleoclimatic and paleoceanographic records through Marine Isotope Stage 19 at the Chiba composite section, central Japan: A key reference for the Early–Middle Pleistocene Subseries boundary

Marine Isotope Stage (MIS) 19 is an important analogue for the present interglacial because of its similar orbital configuration, especially the phasing of the obliquity maximum to precession minimum. However, sedimentary records suitable for capturing both terrestrial and marine environmental changes are limited, and thus the climatic forcing mechanisms for MIS 19 are still largely unknown. The Chiba composite section, east-central Japanese archipelago, is a continuous and expanded marine sedimentary succession well suited to capture terrestrial and marine environmental changes through MIS 19. In this study, a detailed oxygen isotope chronology is established from late MIS 20 to early MIS 18, supported by a U-Pb zircon age and the presence of the Matuyama–Brunhes boundary. New pollen, marine microfossil, and planktonic foraminiferal δ18O and Mg/Ca paleotemperature records reveal the complex interplay of climatic influences. Our pollen data suggest that the duration of full interglacial conditions during MIS 19 extends from 785.0 to 775.1 ka (9.9 kyr), which offers an important natural baseline in predicting the duration of the present interglacial. A Younger Dryas-type cooling event is present during Termination IX, suggesting that such events are linked to this orbital configuration. Millennial- to multi-millennial-scale variations in our δ18O and Mg/Ca records imply that the Subarctic Front fluctuated in the northwestern Pacific Ocean during late MIS 19, probably in response to East Asian winter monsoon variability. The climatic setting at this time appears to be related to less severe summer insolation minima at 65˚N and/or high winter insolation at 50˚N. Our records do not support a recently hypothesized direct coupling between variations in the geomagnetic field intensity and global/regional climate change. Our highly resolved paleoclimatic and paleoceanographic records, coupled with a well-defined Matuyama–Brunhes boundary (772.9 ka; duration 1.9 kyr), establish the Chiba composite section as an exceptional climatic and chronological reference section for the Early–Middle Pleistocene boundary.

East Asian Winter Monsoon Variations and Their Links to Arctic Sea Ice During the Last Millennium, Inferred From Sea Surface Temperatures in the Okinawa Trough

AbstractThe East Asian winter monsoon (EAWM) significantly impacts living conditions in a large part of Asia, and therefore, it is important to understand its major driving mechanisms. Winter sea surface temperature (SSTW) and circulation in the southern Okinawa Trough are today both primarily controlled by the EAWM. Here we present a new SSTW reconstruction for the last millennium based on a diatom record from sediment core MD05‐2908, from the continental slope of the southern Okinawa Trough off northeastern Taiwan. Our reconstruction indicates that SSTW varied between 14.1 and 19.6°C over the past 1,000 years. Changes in SSTW in the southern Okinawa Trough correspond closely to the index of warm winters based on historical documents from the East Asian monsoon domain. This implies that our SSTW record can be used to reconstruct EAWM variability during the last millennium. Comparisons with the reconstructed winter Arctic Oscillation (AO, developed from historical snow anomaly events in Eastern Asia) and Arctic sea ice cover reveal a significant positive correlation between the EAWM and AO during the time interval from 1000–1400 Common Era (C.E.), coinciding with reduced sea ice cover. However, there is no significant correlation with increased sea ice cover during the interval from 1400 to 1700 C.E. This suggests that the reduction in Arctic sea ice may periodically have played a role in strengthening the relationship between the EAWM and the AO during the last millennium and that the current and future reduction in Arctic sea ice may have significant consequences for the EAWM.

Intensified episodes of East Asian Winter Monsoon during the middle through late Holocene driven by North Atlantic cooling events: High-resolution lignin records from the South Yellow Sea, China

The varying intensity of the East Asian Winter Monsoon (EAWM) governs the strength of the counter-clockwise surface circulation of the South Yellow Sea and the redistribution of sediment and terrestrial organic material that had accumulated on the shallow shelf during the summer season into the central part of that basin. We compiled a time series spanning about 6.3 ka of terrestrial lignin proxies from sediment core N02 from Central Yellow Sea Mud that has well-preserved high-resolution sedimentary records (24 yr/cm average spacing). The “hydrodynamic sorting effect” driven by century-scale climate variation in the strength of the EAWM exerts the main underlying control on the variation of lignin proxies in marginal sea sediments, rather than paleovegetation variability in provenance region driven by the East Asian Summer Monsoon (EASM). Our lignin proxies data imply that North Atlantic climate forcing recorded by ice-rafted debris (“Bond cycles”) played a critical role in generating EAWM variability on these centennial timescales during the Holocene. These variations of lignin records are superimposed on general multi-thousand-year trends that appear to mirror the relative frequency and intensity of the El Niño Southern Oscillation (ENSO). Our results indicate that lignin can be adopted as an additional reliable proxy for paleoclimate evolution, at least in South Yellow Sea area.

Low-high latitude interaction forcing on the evolution of the 400 kyr cycle in East Asian winter monsoon records during the last 2.8 Myr

Variability of the East Asian winter monsoon (EAWM), stronger during glacials and weaker during interglacials, has been tightly linked to the wax and wane of the Northern Hemisphere ice sheets (NHIS) via the Siberian High over the last 2.8 million years (Myr). However, the long eccentricity cycle (ca. 400 kyr) in the EAWM record from the late Pliocene to early-Pleistocene (2.8–1.2 Ma) could not be linked to NHIS changes, which lacked the long eccentricity cycle in the Pleistocene. Here, we present the first low latitude EAWM record of the last 2.8 Myr using surface and subsurface temperature difference from the northern South China Sea to evaluate interactions between tropical ocean and EAWM changes. The results show that the EAWM variability displayed significant 400 kyr cycle between 2.8 Ma and 1.2 Ma, with weak (strong) EAWM during high (low) earth orbital eccentricity state. A super El Niño–Southern Oscillation (ENSO) proxy record, calculated using west-east equatorial Pacific sea surface temperature differences, revealed 400 kyr cycles throughout the last 2.8 Myr with warm phase during high eccentricity state. Thus, we propose that super ENSO mean state strongly modulated the EAWM strength through remote forcing to generate the 400 kyr cycle between 2.8 Ma and 1.2 Ma, while low NHIS volume was not sufficient to dominate the EAWM variation as it did over the last 0.9 Myr with 100 kyr cycles in dominance.

Climate‐driven winter variations of Calanus sinicus abundance in the East China Sea

AbstractGlobal environmental changes threaten the sustainable use of resources and raise uncertainties regarding marine populations' responses in a changing Ocean. The pelagic copepods of the genus Calanus play a central role in shelf ecosystems transferring phytoplankton carbon to harvested populations, from boreal to temperate regions. Here we examined a 15‐yr time series of Calanus sinicus abundance in regards to climate forcing in the East China Sea. We identified a compound effect of the Pacific Decadal Oscillation (PDO) and the East Asian Winter Monsoon (EAWM) on environmental conditions in the East China Sea. Such climate influences not only a southward transport of C. sinicus from its population centres into the Taiwan area, but favours advantageous thermal conditions for the species as well. On the interannual scale, our results show that the population size of C. sinicus echoes climate‐driven temperature changes. Hence, the possibility of using the PDO and EAWM variability for assessing and predicting interannual abundance changes of C. sinicus in the East China Sea is considered. The observed close relationship between climate and C. sinicus may promote bottom‐up controls in the pelagic food web, further influencing the southern edge of the species' geographic distribution. Owing to the prominent role this species plays in food web dynamics these results might help integrative fisheries management policies in the heavily exploited East China Sea.

Simple metrics for representing East Asian winter monsoon variability: Urals blocking and western Pacific teleconnection patterns

Instead of conventional East Asian winter monsoon indices (EAWMIs), we simply use two large-scale teleconnection patterns to represent long-term variations in the EAWM. First, the Urals blocking pattern index (UBI) is closely related to cold air advection from the high latitudes towards western Siberia, such that it shows an implicit linkage with the Siberian high intensity and the surface air temperature (SAT) variations north of 40◦N in the EAWM region. Second, the well-known western Pacific teleconnection index (WPI) is connected with the meridional displacement of the East Asian jet stream and the East Asian trough. This is strongly related to the SAT variations in the coastal area south of 40◦N in the EAWM region. The temperature variation in the EAWM region is also represented by the two dominant temperature modes, which are called the northern temperature mode (NTM) and the southern temperature mode (STM). Compared to 19 existing EAWMIs and other well-known teleconnection patterns, the UBI shows the strongest correlation with the NTM, while the WPI shows an equally strong correlation with the STM as four EAWMIs. The UBI–NTM and WPI–STM relationships are robust when the correlation analysis is repeated by (1) the 31-year running correlation and (2) the 8-year high-pass and low-pass filter. Hence, these results are useful for analyzing the large-scale teleconnections of the EAWM and for evaluating this issue in climate models. In particular, more studies should focus on the teleconnection patterns over extratropical Eurasia.

The Linkage between Upper-Level Jet Streams over East Asia and East Asian Winter Monsoon Variability

Abstract This study investigates the linkage between East Asian winter monsoon (EAWM) variability and upper-level jets, with particular focus on the East Asian polar front jet (PJ) and its concurrent variation with the subtropical jet located to the south of the Tibetan Plateau (TSJ). The winter upper-level zonal wind variations over the Asian landmass (70°–120°E) are dominated by two principal modes (i.e., meridional displacement of the PJ and out-of-phase variation in the intensity of the TSJ and PJ) and they are closely linked to the EAWM northern mode and southern mode, respectively. Southward shifting of the PJ concurs with northwestward displacement of the Siberian high (SH), an enhanced northern East Asian trough, leading to cold winter in northern East Asia. Meanwhile the simultaneous TSJ intensification and PJ weakening is linked to an amplified SH, a southward shift of the Aleutian low (AL), a strengthened southern East Asian trough, and a wavelike anomaly pattern extending from western Barents Sea downstream to East Asia at the 500-hPa level. Equatorward shift of the PJ is associated with La Niña conditions in the tropics and sea ice anomalies over the Arctic. An intensified TSJ and weakened PJ are preceded by autumn warming over the central and eastern Pacific Ocean and are linked to circulation anomalies induced by the extensions of stationary Rossby waves, as well as synoptic-scale transient eddy activity anomalies. Therefore, a combination of external forcing and internal atmospheric dynamics plays a role in driving the variations of two leading EOFs, and there is potential for seasonal forecasting of both modes.