The Interannual Variability of East Asian Winter Monsoon and Its Relation to the Summer Monsoon

Based on the NCEP / NCAR reanalysis data the interannual variability of the East Asian winter monsoon (EAWM) is studied with a newly defined EAWM intensity index. The marked features for a strong (weak) winter monsoon include strong (weak) northerly winds along coastal East Asia, cold (warm) East Asian continent and surrounding sea and warm (cold) ocean from the subtropical central Pacific to the tropical western Pacific, high (low) pressure in East Asian continent and low (high) pressure in the adjacent ocean and deep (weak) East Asian trough at 500 hPa. These interannual variations are shown to be closely connected to the SST anomaly in the tropicaI Pacific, both in the western and eastern Pacific. The results suggest that the strength of the EAWM is mainly innuenced by the processes associated with the SST anomaly over the tropical Pacific. The EAWM generally becomes weak when there is a positive SST anomaly in the tropical eastern Pacific (E1 Nino), and it becomes strong when there is a negative SST anomaly (La Nina). Moreover, the SST anomaly in the South China Sea is found to be closely related to the EAWM and may persist to the following summer. Both the circulation at 850 hPa and the rainfall in China confirm the connection between the EAWM and the following East Asian summer monsoon. The possibIe reason for the recent 1998 summer flood in China is briefly discussed too.

How Well do Existing Indices Measure the Strength of the East Asian Winter Monsoon?

Defining the intensity of the East Asian winter monsoon (EAWM) with a simple index has been a difficult task. This paper elaborates on the meanings of 18 existing EAWM strength indices and classifies them into four categories: low level wind indices, upper zonal wind shear indices, east-west pressure contrast indices, and East Asian trough indices. The temporal/spatial performance and prediction potential of these indices are then analyzed for the 1957-2001 period. It reveals that on the decadal timescale, most indices except the east-west pressure contrast indices can well capture the continuous weakening of the EAWM around 1986. On the interannual timescale, the low level wind indices and East Asian trough indices have the best predictability based on knowledge of the El Nio-Southern Oscillation and Arctic Oscillation, respectively. All the 18 existing indices can well describe the EAWM-related circulation, precipitation, and lower tropospheric air temperature anomalies. However, the variations of surface air temperature over large areas of central China cannot be well captured by most indices, which is possibly related to topographic effects. The results of this study may provide a possible reference for future studies of the EAWM.

Predictability of the East Asian Winter Monsoon Interannual Variability as Indicated by the DEMETER CGCMS

The interannual variability of East Asian winter monsoon(EAWM) circulation from the Development of a European Multi-Model Ensemble(MME) System for Seasonal to Inter-Annual Prediction(DEMETER) hindcasts was evaluated against observation reanalysis data.We evaluated the DEMETER coupled general circulation models(CGCMs)' retrospective prediction of the typical EAWM and its associated atmospheric circulation.Results show that the EAWM can be reasonably predicted with statistically significant accuracy,yet the major bias of the hindcast models is the underestimation of the related anomalies.The temporal correlation coefficient(TCC) of the MME-produced EAWM index,defined as the first EOF mode of 850hPa air temperature within the EAWM domain(20-60 N,90-150 E),was 0.595.This coefficient was higher than those of the corresponding individual models(range:0.39-0.51) for the period 1969-2001;this result indicates the advantage of the super-ensemble approach.This study also showed that the ensemble models can reasonably reproduce the major modes and their interannual variabilities for sea level pressure,geopotential height,surface air temperature,and wind fields in Eurasia.Therefore,the prediction of EAWM interannual variability is feasible using multimodel ensemble systems and that they may also reveal the associated mechanisms of the EAWM interannual variability.

Relationship between Bering Sea Ice Cover and East Asian Winter Monsoon Year-to-Year Variations

In this study,the relationship between year-to-year variations in the Bering Sea ice cover(BSIC) and the East Asian winter monsoon(EAWM) for the period 1969-2001 was documented.The time series of total ice cover in the eastern Bering Sea correlated with the EAWM index at 0.49,indicating that they are two tightly related components.Our results show that the BSIC was closely associated with the simultaneous local and large-scale atmosphere over the Asian-northern Pacific region.Heavy BSIC corresponded to weaker EAWM circulations and light BSIC corresponded to stronger EAWM circulations.Thus,the BSIC should be considered as one of the possible factors affecting the EAWM variation.

Interference of the East Asian Winter Monsoon in the Impact of ENSO on the East Asian Summer Monsoon in Decaying Phases

The variability of the East Asian winter monsoon(EAWM) can be divided into an ENSO-related part(EAWMEN) and an ENSO-unrelated part(EAWMres). The influence of EAWMreson the ENSO–East Asian summer monsoon(EASM) relationship in the decaying stages of ENSO is investigated in the present study. To achieve this, ENSO is divided into four groups based on the EAWMres:(1) weak EAWMres–El Nio(WEAWMres–EN);(2) strong EAWMres–El Nio(SEAWMres– EN);(3) weak EAWMres–La Nia(WEAWMres–LN);(4) strong EAWMres–La Nia(SEAWMres–LN). Composite results demonstrate that the EAWMresmay enhance the atmospheric responses over East Asia to ENSO for WEAWMres–EN and SEAWMres–LN. The corresponding low-level anticyclonic(cyclonic) anomalies over the western North Pacific(WNP) associated with El Nio(La Nia) tend to be strong. Importantly, this feature may persist into the following summer, causing abundant rainfall in northern China for WEAWMres–EN cases and in southwestern China for SEAWMres–LN cases. In contrast, for the SEAWMres–EN and WEAWMres–LN groups, the EAWMrestends to weaken the atmospheric circulation anomalies associated with El Nio or La Nia. In these cases, the anomalous WNP anticyclone or cyclone tend to be reduced and confined to lower latitudes, which results in deficient summer rainfall in northern China for SEAWMres–EN and in southwestern China for WEAWMres–LN. Further study suggests that anomalous EAWMresmay have an effect on the extra-tropical sea surface temperature anomaly, which persists into the ensuing summer and may interfere with the influences of ENSO.

Low- and Mid-High Latitude Components of the East Asian Winter Monsoon and Their Reflecting Variations in Winter Climate over Eastern China

The present study defines a low-latitude component (regionally averaged winter 1000-hPa V-winds over 10 25°N, 105 135°E) and a mid-high-latitude component (regionally averaged winter 1000-hPa V-winds over 30 50°N, 110 125°E) of the East Asian winter monsoon (EAWM), which are denoted as EAWM-L and EAWM-M, respectively. The study examines the variation characteristics, reflecting variations in winter climate over eastern China, and associated atmospheric circulations corresponding to the two components. The main results are as follows: 1) the EAWM-L and EAWM-M have consistent variation in some years but opposite variations in other years; 2) the EAWM-M index mainly reflects the extensive temperature variability over eastern China, while the EAWM-L index better reflects the variation in winter precipitation over most parts of eastern China; and 3) corresponding to the variation in the EAWM-M index, anomalous winds over the mid-high latitudes of East Asia modulate the southward invasion of cold air from the high latitudes and accordingly affect temperatures over eastern China. In combination with the variation in the EAWM-L index, anomalous low-latitudinal winds regulate the water vapor transport from tropical oceans to eastern China, resulting in anomalous winter precipitation. These pronounced differences between the EAWM-L and the EAWM-M suggest that it is necessary to explore the monsoons' individual features and effects in the EAWM study.

Relationship Between East Asian Winter Monsoon and Summer Monsoon

Using National Centers for Environmental Prediction/National Centre for Atmospheric Research(NCEP/NCAR) reanalysis data and monthly Hadley Center sea surface temperature(SST) data,and selecting a representative East Asian winter monsoon(EAWM) index,this study investigated the relationship between EAWM and East Asian summer monsoon(EASM) using statistical analyses and numerical simulations.Some possible mechanisms regarding this relationship were also explored.Results indicate a close relationship between EAWM and EASM:a strong EAWM led to a strong EASM in the following summer,and a weak EAWM led to a weak EASM in the following summer.Anomalous EAWM has persistent impacts on the variation of SST in the tropical Indian Ocean and the South China Sea,and on the equatorial atmospheric thermal anomalies at both lower and upper levels.Through these impacts,the EAWM influences the land-sea thermal contrast in summer and the low-level atmospheric divergence and convergence over the Indo-Pacific region.It further affects the meridional monsoon circulation and other features of the EASM.Numerical simulations support the results of diagnostic analysis.The study provides useful information for predicting the EASM by analyzing the variations of preceding EAWM and tropical SST.

Projections of the East Asian Winter Monsoon under the IPCC AR5 Scenarios Using a Coupled Model:IAP_FGOALS

Responses of the East Asian winter monsoon(EAWM) in future projections were studied based on two core future projections of CMIP5 in coordinated experiments with the IAP-coupled model FGOALS2-s.The projected changes of EAWM in climatology,seasonality,and interannual variability are reported here;the projections indicated strong warming in winter season.Warming increased with latitude,ranging from 1 C to 3 C in the Representative Concentration Pathways simulation RCP4.5 projection(an experiment that results in additional radiative forcing of ～4.5 W m 2 in 2100) and from 4 C to 9 C in the RCP8.5 projection(an experiment that results in additional radiative forcing of ～8.5 W m 2 in 2100).The northerly wind along the East Asian coastal region became stronger in both scenarios,indicating a stronger EAWM.Accordingly,interannual variability(described by the standard deviation of temperature) increased around the South China Sea and lower latitudes and decreased over eastern China,especially in North China.The two EAWM basic modes,defined by the temperature EOF analysis over East Asia,were associated with the Arctic Oscillation(AO) and stratospheric polar vortex.The future projections revealed more total variance attributable to the secondary mode,suggesting additional influences from the stratosphere.The correlation between AO and the leading mode decreased,while the correlation between AO and the secondary mode increased,implying increased complexity regarding the predictability of EAWM interannual variations in future projections.

Atmospheric Circulation Cells Associated with Anomalous East Asian Winter Monsoon

Atmospheric circulation cells associated with anomalous East Asian Winter Monsoon (EAWM) were studied using the 1948/49 to 2002/03 NCEP/NCAR reanalysis and NCAR CAM3 AGCM simulations with monthly global sea surface temperatures from 1950 to 2000. Several atmospheric cells in the Pacific [i.e., the zonal Walker cell (ZWC) in the tropic, the Hadley cell in the western Pacific (WPHC), the midlatitude zonal cell (MZC) over the central North Pacific, and the Hadley cell in the eastern Pacific (EPHC)] are associated with anomalous EAWM. When the EAWM is strong, ZWC, WPHC, and MZC are enhanced, as opposed to EPHC. The anomalous enhanced ZWC is characterized by air parcels rising in the western tropical Pacific, flowing eastward in the upper troposphere, and descending in the tropical central Pacific before returning to the tropical western Pacific. The enhanced MZC has characteristics opposite those of the enhanced ZWC in the central North Pacific. The anomalous WPHC shows air parcels rising in the western Pacific, as in the case of ZWC, followed by flowing northward in the upper troposphere and descending in the west North Pacific, as in the case of the enhanced MZC before returning to the western tropical Pacific. The anomalous EPHC is opposite in properties to the anomalous WPHC. Opposite characteristics are found during the weak EAWM period. The model simulations and the observations show similar characteristics and indicate the important role of sea surface temperature. A possible mechanism is proposed to link interannual variation of EAWM with the central-eastern tropical Pacific sea surface temperature anomaly (SSTA).

Anti-Phase Relationship Between the East Asian Winter Monsoon and Summer Monsoon During the Holocene?

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 ^(14)C 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.

Relationships between intensity of the Kuroshio current in the East China Sea and the East Asian winter monsoon

Based on satellite altimeter and reanalysis data,this paper studies the relationships between the intensity of the Kuroshio current in the East China Sea(ECS) and the East Asian winter monsoon(EAWM).The mechanisms of their possible interaction are also discussed.Results indicate that adjacent transects show consistent variations,and on an interannual timescale,when the EAWM is anomalously strong(weak),the downstream Kuroshio in the ECS is suppressed(enhanced) in the following year from February to April.This phenomenon can be attributed to both the dynamic effect(i.e.,Ekman transport) and the thermal effect of the EAWM.When the EAWM strengthens(weakens),the midstream and downstream Kuroshio in the ECS are also suppressed(intensified) during the following year from October to December.The mechanisms vary for these effects.The EAWM exerts its influence on the Kuroshio's intensity in the following year through the tropospheric biennial oscillation(TBO),and oceanic forcing is dominant during this time.The air-sea interaction is modulated by the relative strength of the EAWM and the Kuroshio in the ECS.The non-equivalence of spatial scales between the monsoon and the Kuroshio determines that their interactions are aided by processes with a smaller spatial scale,i.e.,local wind stress and heating at the sea surface.

Predictability of the East Asian Winter Monsoon Indices by the Coupled Models of ENSEMBLES

The seasonal predictability of various East Asian winter monsoon(EAWM) indices was investigated in this study based on the retrospective forecasts of the five state-of-the-art coupled models from ENSEMBLES for a 46-year period of 1961–2006. It was found that the ENSEMBLES models predict five out of the 21 EAWM indices well, with temporal correlation coefficients ranging from 0.54 to 0.61. These five indices are defined by the averaged lower-tropospheric winds over the low latitudes(south of 30°N). Further analyses indicated that the predictability of these five indices originates from their intimate relationship with ENSO. A cross-validated prediction, which took the preceding(November) observed Nino3.4index as a predictor, gives a prediction skill almost identical to that shown by the model. On the other hand, the models present rather low predictability for the other indices and for surface air temperature in East Asia. In addition, the models fail to reproduce the relationship between the indices of different categories, implying that they cannot capture the tropical–extratropical interaction related to EAWM variability. Together, these results suggest that reliable prediction of the EAWM indices and East Asian air temperature remains a challenge.

Influence of Low-frequency Solar Forcing on the East Asian Winter Monsoon Based on HadCM3 and Observations

In this study, we investigate the influence of low-frequency solar forcing on the East Asian winter monsoon(EAWM)by analyzing a four-member ensemble of 600-year simulations performed with Had CM3(Hadley Centre Coupled Model,version 3). We find that the EAWM is strengthened when total solar irradiance(TSI) increases on the multidecadal time scale. The model results indicate that positive TSI anomalies can result in the weakening of Atlantic meridional overturning circulation, causing negative sea surface temperature(SST) anomalies in the North Atlantic. Especially for the subtropical North Atlantic, the negative SST anomalies can excite an anomalous Rossby wave train that moves from the subtropical North Atlantic to the Greenland Sea and finally to Siberia. In this process, the positive sea-ice feedback over the Greenland Sea further enhances the Rossby wave. The wave train can reach the Siberian region, and strengthen the Siberian high. As a result, low-level East Asian winter circulation is strengthened and the surface air temperature in East Asia decreases. Overall,when solar forcing is stronger on the multidecadal time scale, the EAWM is typically stronger than normal. Finally, a similar linkage can be observed between the EAWM and solar forcing during the period 1850–1970.

Stationary Wave Activity Associated with the East Asian Winter Monsoon Pathway

The pathway of the East Asian winter monsoon(EAWM) that usually leads to the out-of-phase pattern of surface air temperature between northern and southern East Asia is an important feature in the variability of the EAWM besides its strength.Using the European Centre for Medium-Range Weather Forecasts 40-year(ERA40) reanalysis dataset,this study investigates the pathway-related stationary wave activity to explore the mechanism of the interannual variations in the EAWM pathway.It reveals that when the southern pathway of the EAWM is strong,the phase of the climatological stationary wave tends to be shifted westward significantly in both the horizontal and vertical directions by an anomalous wavenumber 2 pattern at mid-latitudes,whereas the changes are relatively small in the subtropics.The horizontal changes in the stationary wave phase facilitate a north-south-oriented East Asian trough in the middle troposphere that eventually produces the strong southern pathway of the EAWM.The vertical changes in the stationary wave,in contrast,feature a westward-tilted phase line with height over the North Pacific,indicating enhanced upward propagation of waves into the stratosphere.This result suggests that the phase of stationary waves at mid-latitudes dominate the interannual variations in the EAWM pathway.Moreover,it supports our previous interpretation of the possible role of the North Pacific sea surface temperature(SST) in the EAWM pathway variability.It also implies that the excitation of anomalous mid-latitude stationary waves may be the key in the response of the EAWM pathway to the North Pacific SST.

Simulated and projected relationship between the East Asian winter monsoon and winter Arctic Oscillation in CMIP5 models

观测资料显示,东亚冬季风与同期AO的关系在20世纪80年代发生年代际增强。通过考察CMIP5模式对这一现象的模拟情况,发现GFDL-ESM2M、GISS-E2-H和MPI-ESM-MR这3个模式能够再现EAWM-AO关系的年代际增强。进一步考察这3个模式的集合平均结果(MME)发现,冬季AO对EAWM环流系统以及东亚气温的影响均发生明显的年代际变化。通过考察MME模拟的EP通量结果发现,自20世纪80年代开始,在对流层从高纬度地区传播到副热带地区的EP通量异常明显增强,这是MME模拟结果中EAWM-AO关系发生年代际增强的主要原因。

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.

Evaluation of the Twentieth Century Reanalysis Dataset in Describing East Asian Winter Monsoon Variability

The Twentieth Century Reanalysis(20thCR)dataset released in 2010 covers the period 1871–2010 and is one of the longest reanalysis datasets available worldwide.Using ERA-40,ERA-Interim and NCEP–NCAR reanalysis data,as well as HadSLP2 data and meteorological temperature records over eastern China,the performances of 20thCR in reproducing the spatial patterns and temporal variability of the East Asian winter monsoon(EAWM)are examined.Results indicate that 20thCR data:(1)can accurately reproduce the most typical configuration patterns of all sub-factors involved in the EAWM system,albeit with some diferences in the main circulation fields over East Asia in comparison to ERA-40 reanalysis data;(2)is reliable and stable in describing the temporal variability of EAWM since the 1930s;and(3)can describe the high-frequency variability of EAWM better than the low-frequency fluctuations,especially in the early period.In conclusion,caution should be taken when using 20thCR data to study interdecadal variabilities or long-term trends of the EAWM,especially prior to the 1930s.

Improved simulation of the East Asian winter monsoon interannual variation by IAP/LASG AGCMs

东亚冬季风的模拟性能一直是检验气候模式的重要指标。本文对比分析了LASG新旧两个版本大气环流模式对东亚冬季风年际变率的模拟性能。结果表明,GAMIL2模拟的东亚冬季风指数与观测的相关系数为0.71,相较于GAMIL1(0.37)有明显改进。主要原因是GAMIL2改进了云参数化方案,能够更合理的再现加热率对厄尔尼诺的响应,有助于激发菲律宾海反气旋,从而改进东亚冬季风的模拟。

A STUDY ON RELATION BETWEEN EAST ASIAN WINTER MONSOON AND CLIMATE CHANGE DURING RAINING SEASON IN CHINA

Based on the data of NCEP, OLR and rainfall of China, we studied the influences of the East Asian winter monsoon activities on the precipitation during the raining season over China by correlation analysis and composite analysis. The result shows that annual and interdecadal change of East Asian winter monsoon is distinct. It is strong from 1950s to the middle of 1980s but weak after the middle of 1980s. The effect of abnormal winter monsoon on the precipitation during raining season is significant over the middle and lower reaches of the Changjiang River basin. It is revealed that the precipitation will increase when preceding winter monsoon is weak but decrease when preceding winter monsoon is strong. In this paper, some appropriate reasons are given to explain the abnormal rainfall by analyzing the distribution of SSTA and the variation of summer circulation. It is pointed out definitely that the variation of SSTA and summer circulation is a primary cause for abnormal rainfall over the middle and lower reaches of the Changjiang River.

East Asian Winter Monsoon record from the environmental sensitive grain size component of QF Old Red Sand, Haitan Island, China

The "Old Red Sand" is widely distributed along the coast of Fujian Province, China. Most studies have been carried out from aspects of the origin, age and laterization of the "Old Red Sand", but this paper focused on reconstructing the history of the Asian Winter Monsoon change. On the basis of granulometric analysis of high-resolution samples, we have obtained environmental sensitive grain size component (ESGSC) from the Qingfeng (QF) profile by using the grain size-standard deviation method, which proves that the selected ESGSC is an important climate proxy. The mean grain size of this ESGSC could be used to reconstruct the East Asian Winter Monsoon (EAWM) intensity. As such, the history of the EAWM change since 44.0 ka reconstructed here reveals three main phases based on chronology dates of previous researches: (1) 44.0-25.5 ka B.P., the EAWM is relatively weak but increases gradually with fluctuations; (2) 25.5-15.5 ka B.P., relatively strong with high frequency fluctuations; (3) 15.5-7.1 ka B.P., with a weaker winter monsoon, but during 11-10 ka B.P. is remarkably enhanced. The EAWM recorded by mean grain size of the two neighboring sections have a better repeatability, so the millennial scales oscillation should be a reliable signal of the EAWM intensity. The climate recorded by ESGSC of the QF "Old Red Sand" compared to δ 18 O of Hulu Cave stalagmites and Greenland GISP2 ice cores shows a good consistency, especially in detail, the YD event and four Heinrich events are all recorded, but the signal of D-O cycles was relatively weak.