Seasonal Prediction Skill and Biases in GloSea5 Relating to the East Asia Winter Monsoon

The simulation and prediction of the climatology and interannual variability of the East Asia winter monsoon(EAWM),as well as the associated atmospheric circulation,was investigated using the hindcast data from Global Seasonal Forecast System version 5(GloSea5),with a focus on the evolution of model bias among different forecast lead times.While GloSea5 reproduces the climatological means of large-scale circulation systems related to the EAWM well,systematic biases exist,including a cold bias for most of China’s mainland,especially for North and Northeast China.GloSea5 shows robust skill in predicting the EAWM intensity index two months ahead,which can be attributed to the performance in representing the leading modes of surface air temperature and associated background circulation.GloSea5 realistically reproduces the synergistic effect of El Niño–Southern Oscillation(ENSO)and the Arctic Oscillation(AO)on the EAWM,especially for the western North Pacific anticyclone(WNPAC).Compared with the North Pacific and North America,the representation of circulation anomalies over Eurasia is poor,especially for sea level pressure(SLP),which limits the prediction skill for surface air temperature over East Asia.The representation of SLP anomalies might be associated with the model performance in simulating the interaction between atmospheric circulations and underlying surface conditions.

EFFECTS OF VARIATION OF WINTER SEA-ICE AREA IN KARA AND BARENTS SEAS ON EAST ASIA WINTER MONSOON

By analyzing the observation data and performing the numerical simulation tests,it is shown that the Kara and the Barents Sea area is a key region to influence climate variation over the Northern Hemisphere.The variation of winter sea-ice area in the key region is closely associated with that of the EU teleconnection pattern at 500 hPa and East Asia winter monsoon(EAWM) intensity.When a heavy sea-ice prevails in the key region,the EU teleconnection pattern at 500 hPa is excited easily(there are positive 500 hPa height anomalies over around Japan and West Europe),and winter Siberia high is weakened,meanwhile,sea level pressure(SLP)has positive anomalies over the Northern Pacific.Therefore,EAWM will be weakened,winter temperature over East Asia is above normal and the frequency of cold-air activity in February in China will be decreased.When the light sea-ice occurs in the key region,the results will be opposite.

A possible way to extract a stationary relationship between ENSO and the East Asian winter monsoon

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.

East Asia Winter Monsoon changes inferred from environmentally sensitive grain-size component records during the last 2300 years in mud area southwest off Cheju Island,ECS

Environmentally sensitive grain-size component (ESGSC) extracted from grain-size data of a sediment core B2, which were retrieved from mud area southwest off Cheju Island (MACI), East China Sea (ECS), can be used to indicate the variations of East Asia Winter Monsoon (EAWM), with high (low) content/mean-size of ESGCS denote to strong (weak) EAWM. Combined with AMS14C datings core B2 provides a continuous high-resolution record of EAWM changes over the past 2300 years, with an average resolution of 13 years. The results show that the variations of EAWM are con-sistent with temperature changes inferred from historical documents in eastern China over the past 2300 years, from which four climate stages may be identified. In stages before 1900 aBP (50 AD) and 1450―780 aBP (50―1170 AD) the EAWM were comparatively weak, corresponding to warm climate periods in eastern China, respectively. And in stages of 1900―1450 aBP (50―500 AD) and 780―219 aBP (1170―1731 AD) the EAWM were strongly developed, which correspond well to climate changes of two cold periods in eastern China. It is also shown from this study that the stage at 780―219 aBP (1170―1731 AD) was the coldest climate period during the last 2300 years and could be, therefore, related to the Little Ice Age (LIA). Climatic fluctuations appeared obviously in all the four stages, and two climate events of abrupt changes from warm to cold occurred at around 1900 aBP (50 AD) and 780 aBP (1170 AD), of which the latter is probably related to globe-scale changes of atmospheric circulation at that time.

The strong winter monsoon in East Asia and El Nino

The relationship between meridional wind in mid - latitudes of East Asia and SST in the Equatorial Eastern Pacific is analysed in this paper. It is pointed out that there exist close relations between the seasonal changes of the meridional wind in mid - latitudes of East Asia and SST in the Equatorial Eastern Pacific. The intensification of north winds over East Asia also plays an important role in the rise of SST in Equatorial Eastern Pacific one year later. The strong winter monsoon usually occurs in previous winter of El Nino and it causes low temperature to a great extent in China . The low temperature in China can be regarded as a precursor of El Nino.

Characteristics of Atmospheric Circulation Associated with Cold Surge Occurrences in East Asia:A Case Study During 2005/06 Winter

The characteristics of the upper-level circulation and thermodynamical properties for the period when two distinct cold surges broke out over East Asia during the 2005/06 winter are investigated. From early December 2005 to early January 2006, exceptionally cold weather lasted for approximately one month due to two successive cold surges that took place on 2 December 2005 and 2 January 2006, respectively. This study reveals that both involve the upper-tropospheric circulation, which induces the amplification and expansion of the surface Siberian high toward East Asia, but arose from different causes： the former is caused by the upper-level blocking originated from the North Pacific and the latter is caused by the upper-level wave train across the Eurasian Continent. In particular, it is suggested that the lower-tropospheric anomalous wind caused by upper-level circulation anomalies and a steep meridional temperature gradient amplified by phase-locked annual cycle combined to induce very strong cold advection in East Asia, which resulted in exceptionally cold weather that lasted for several weeks. The present results emphasize that the characteristics of the upper-tropospheric circulation can be considered as important precursors to cold surge occurrences in East Asia.

A FURTHER STUDY ON INTERACTION BETWEEN ANOMALOUS WINTER MONSOON IN EAST ASIA AND EL NINO

The interaction between anomalous winter monsoon in East Asia and El Nino is further stud- ied in this paper.The new results still more proved a previous conclusion:there are clear interac- tions between El Nino and winter monsoon in East Asia.The continual westerly burst and stronger cumulus convection over the equatorial central-western Pacific caused by stronger winter monsoon in East Asia can respectively excite anomalous oceanic Kelvin wave and stronger atmo- spheric intraseasonal oscillation in the tropics,then excite the El Nino event through air-sea inter- action.In El Nino winter,there are warmer and weaker winter monsoons in East Asia.The El Ni- no will still reduce the intensity of intraseasonal oscillation and leads it to be barotropic structure.

AN ANALYSIS OF THE WINTER EXTREME PRECIPITATION EVENTS ON THE BACKGROUND OF CLIMATE WARMING IN SOUTHERN CHINA

Based on daily precipitation and monthly temperature data in southern China, the winter extreme precipitation changes in southern China have been investigated by using the Mann-Kendall test and the return values of Generalized Pareto Distribution. The results show that a winter climate catastrophe in southern China occurred around i99I, and the intensity of winter extreme precipitation was strengthened after climate wanning. The anomalous circulation characteristics before and after the climate wanning was further analyzed by using the U.S. National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis data. It is found that the tropical winter monsoon over East Asia is negatively correlated with the precipitation in southeastern China. After climate warming the meridionality of the circulations in middle and high latitudes increases, which is favorable for the southward movement of the cold air from the north. In addition, the increase of the temperature over southern China may lead to the decrease of the differential heating between the continent and the ocean. Consequently, the tropical winter monsoon over East Asia is weakened, which is favorable for the transport of the warm and humid air to southeastem China and the formation of the anomalous convergence of the moisture flux, resulting in large precipitation over southeastern China. As a result, the interaction between the anomalous circulations in the middle and high latitudes and lower latitudes after the climate warming plays a major role in the increase of the winter precipitation intensity over southeastem China.

Wintertime Cyclone Activity and Its Relation to Precipitation over China

The authors examined the variability in wintertime cyclone activity and storm tracks and their relation to precipitation over China for the period 1951-2006 using the observational data.Two apparent modes of variability were assumed for the cyclone activity and storm tracks.The first mode describes the oscillation in the strength of the storm tracks in East Asia,which significantly increased since the mid-1980s,whereas the second mode describes a seesaw oscillation in the storm track strength between the Central-Southeast China and northem East Asia.The storm tracks over the Central-Southeast China have increased since the late 1960s.The possible causes for the variation of the cyclone activity and storm tracks are also explored.It is shown that wintertime precipitation,which has increased since the mid-1980s,concentrates in Central-Southeast China.The enhancement may be caused by the first mode of variability of storm tracks,whereas the interannual variability of precipitation may be linked to the second mode of the storm track variability.

近2ka以来东海内陆架泥质区记录的高分辨率古气候演化

通过对位于东海内陆架泥质区中部的MZ02柱样岩芯进行粒度、常量元素、AMS14C分析,获得了粒度和常量元素随时间变化的高分辨率曲线。结果表明,近2 ka以来研究区沉积环境稳定,以沿岸流控制的浅海沉积为主,沉积物中CaO/K2O,MgO/Al2O3和MnO/Na2O比值的变化与我国东部气候变化序列具有较好的一致性,证明这些元素地球化学指标可以作为古气候变化的高分辨率替代性指标。近2 ka以来CaO/K2O、MgO/Al2O3和MnO/Na2O共同识别出的7次极值揭示了同期的降温事件,分别发生在～1 480 a BP(C1),～1 200 a BP(C2),～1 020 a BP(C3),～780 a BP(C4),～580 a BP(C5),～330 a BP(C6),～120 a BP(C7),且在其他区域不同介质中也能找到相应的降温证据,揭示了气候变化的区域性以至全球性联系。

东亚地区冬季风对气溶胶传输和分布的影响研究

随着东亚地区经济高速发展,气溶胶成为最主要的大气污染物之一,其时空分布受到东亚季风气候的影响.本研究利用MODIS(Moderate-Resolution Imaging Spectroradiometer)和TOMS(Total Ozone Meteorological Satellite)气溶胶卫星产品以及NCEP(National Centers for Environmental Prediction)月均气象场再分析资料,统计分析了1979—2011年东亚地区气溶胶光学厚度的分布特征以及冬季风的大气环流特征,同时分析了东亚冬季风对气溶胶传输和分布的影响.结果表明,东亚冬季风存在明显的年际和年代际差异,年际变化幅度较大.1979—2011年东亚冬季风出现逐渐减弱的趋势.近10年来东亚地区气溶胶光学厚度呈现上升趋势,主要是由于人类活动导致气溶胶排放量增加.东亚地区冬季风对气溶胶的分布有较大影响,强冬季风年会加强气溶胶的向南输送,同时降水增加导致气溶胶湿清除增大,使东亚气溶胶减少.在风场和降水对气溶胶的影响中,降水的清除作用更加明显.

冬季北大西洋涛动极端异常变化与东亚冬季风

依据资料分析发现，冬季北大西洋涛动指数与冬季西伯利亚高压范围呈反向变化关系，冬季北大西洋涛动指数异常偏高（ 低） 时期，３０ ～５０ｏＮ 的亚洲大陆中部气压显著偏低（ 高） ，致使冬季西伯利亚高压和东亚冬季风减弱（ 增强） 以及亚洲大陆北部气温显著偏高（ 低） 。冬季西伯利亚高压范围异常变化对北大西洋涛动没有显著的影响，其对北半球海平面气压、８５０ ｈＰａ 温度的影响也明显要弱于北大西洋涛动的影响。

夏季索马里急流的建立及其影响机制

定义了夏季索马里急流(SSMJ)的建立指数,从而确定了1948—2002年的SSMJ建立日期,并以此为基础研究了SSMJ建立过程以及前冬海陆热力异常和冬季风异常对其建立早晚的影响。结果表明:SSMJ的建立是亚洲季风爆发的最早信号;其建立过程受到马斯克林高压、中非低压以及阿拉伯高压等非洲—印度洋系统的影响,而印度低压的发展有利于SSMJ越过赤道后向东转向;夏季索马里急流建立时间的年际变化反映了北半球冬季海陆热力差异的年际异常;强(弱)东亚冬季风时,次年春季SSMJ建立偏迟(早)。

早、中更新世东亚冬季风强度的快速变化

对黄土高原中部洛川黄土堆积进行了系统的粒度和磁化率测量，以黄土－古土壤中的粗颗粒组分，即＞３０μｍ颗粒的百分含量作为冬季风强度代用指标，根据一个独立的时间标尺，发现在１４５～１６５、２４０～２８０、３２０～３５０、３９０～４４０、６００～６４０、８６０～８９０、９００～９３０和１３３０～１４００ｋａＢ．Ｐ．东亚冬季风强度存在千年尺度快速变化的特征，冬季风加强事件的持续时间在１．４～７．２ｋａ之间，变化幅度也不相同；周期分析结果表明，这些古气候变化存在１．８９～４．０ｋａ之间的周期，由于时间标尺的精度还有待于进一步提高，在这里没有把冬季风强度变化与北大西洋沉积物记录的古气候事件进行对比，但是，实验结果证明在早。

东亚冬季风指数的分类和比较

在回顾了2009年以前定义过的冬季风指数的基础上,按照定义要素的不同,进行了分类及序列延长计算,并将现有的冬季风指数分为海陆气压差类(4个)、高压特征类(3个)、风场特征类(9个)、环流特征类(4个)和综合类(2个)。研究了这些冬季风指数的年际及年代际变化趋势及其周期变化,分析了各指数之间的相关性,以及冬季风指数对中国冬季大陆气温变化的指示性。结果表明:东亚冬季风存在缓慢减弱的变化趋势,主要呈现出准6a,准11a和准17a的周期振荡特征。同类别指数之间的相关性要优于不同类别的。东亚冬季风指数与中国冬季大陆气温相关性普遍好的地区主要在河套及内蒙古中部、华南和东南沿海、四川盆地等。

冬季北极喀拉海、巴伦支海海冰面积变化对东亚冬季风的影响

通过大量的数据分析发现，冬季喀拉海、巴伦支海海区是影响东亚以及北半球气候变化的关键区之一，该海区海冰面积变化与大气５００ｈＰａ高度场的ＥＵ遥相关型以及东亚冬季风强、弱之间存在密切的关系。冬季该海区海冰偏多，则５００ｈＰａ高度场容易出现ＥＵ遥相关型（日本及西欧５００ｈＰａ高度场偏高），亚洲大陆上的冷高压减弱。而北太平洋海域海平面气压升高，致使东亚冬季风偏弱以及２月份入侵我国的冷空气次数减少；而冬季该海区海冰偏少时，情况正好相反。

中国地面气温年际和年代际变化及其与北冰洋涛动指数的关系

利用中国气象局气候中心数据库1958—1994年中国160个测站的月平均温度资料, 分析了中国37年气温的年际和年代际变化及其与北冰洋涛动指数的关系。结果表明: (1)1958—1994 年以来,东北地区全年、秋季和冬季温度上升都很明显, 其中冬季最明显; 新疆冬季温度升高也很明显; 华南夏季温度明显升高。(2)通过对各区温度的年代际变化检验可知, 东北全年、秋季和冬季 1983 年以后温度有非常显著的升高; 新疆冬季1976年以后温度也有显著升高; 华南夏季 1976 年以后温度有明显升高。(3)从全国来看, 北方各区气候变暖要比南方显著一些, 特别是冬季。(4)北冰洋涛动与我国东北温度有十分密切的联系, 当AO指数偏小时, 冬季冰岛附近海平面气压偏低, 西伯利亚高压范围缩小,东亚冬季风比较弱, 我国东北冬半年的温度出现明显上升。

南方极端雨雪冰冻过程东亚冬季风环流特征及与EINino/La Nina事件的关系

根据南方极端雨雪冰冻过程的定义,确定1964、1969、1977、1984、2008年的强降水、降温过程为南方极端雨雪冰冻过程。对发生在EINino/LaNina事件之后的南方极端雨雪冰冻过程的分析表明:EINino/LaNina是造成中国东部1月降水异常的一个主要原因,但不能解释气温异常。前一年秋季热带中东太平洋发生暖事件时,利于1月降水黄河流域偏少,长江以南偏多,而发生冷事件时,则利于1月降水黄河流域偏多,长江以南偏少。南方极端雨雪冰冻过程期间对流层低层和高层矢量风距平场表明:发生月对流层低层在1977、1984年南方极端雨雪冰冻过程中,北太平洋出现大范围气旋环流异常,中国长江中下游及以南至菲律宾出现气旋环流异常,长江中下游及以南为东风距平控制。1964、1969、2008年北太平洋出现大范围反气旋环流异常,中国长江中下游及以南出现大片偏南风距平。其共同点是均存在洋面上空暖湿空气向长江中下游及以南地区的输送。南方极端雨雪冰冻过程的前一年11月北太平洋无一例外地出现大范围气旋环流异常,发生月对流层高层副热带西风急流在中国黄海至日本一带较常年都有不同程度的偏强。

东亚冬季风年际变化的ENSO信息 Ⅰ.观测资料分析

利用１９５０～１９８９年４０年的全球月平均资料，详细讨论了东亚冬季风的年际变化特征，分析结果表明东亚冬季风年际变化中包含有明显的ＥＮＳＯ信号，也就是说东亚冬季风活动与ＥＮＳＯ的发生有明显的关系，大多数ＥＩＮino事件爆发后东亚冬季风偏弱，而大多数ＬａＮｉｎａ爆发后东亚冬季风偏强。通过对这４０年间的１０次ＥＩＮｉｎｏ和７次ＬａＮｉｎａ事件的合成分析，结果表明ＥＩＮino。冬半年东亚５００ｈＰａ位势高度为正距平、海平面气压为负距平，即东亚冬季风偏弱，阿留申及北美地区呈现出明显的类似ＰＮＡ型的异常环流形势；ＬａＮｉｎａ冬半年东亚以至于北半球大气环流异常形势与ＥＩＮｉｎｏ的相反。同时资料分析也表明，在大多数ＥＩＮｉｎｏ（ＬａＮｉｎａ）爆发前东亚冬季风偏强（弱）。另外，功率谱分析结果表明，东亚冬季风有显著的３～５年和准２年的变化周期，这从另一方面说明了东亚冬季风的年际异常中包含有显著的ＥＮＳＯ信息。

东亚冬季风异常对区域气溶胶分布的影响

气溶胶已是东亚地区最主要的大气污染物之一,其时空分布会受到东亚季风气候的影响。利用2000~2014年MODIS/AOD(Moderate-resolution Imaging Spectroradiometer/Aerosol Optical Depth)和NCEP月平均气象场再分析资料,本研究分析了东亚冬季风长期变化趋势、气溶胶年际变化规律,探讨了东亚冬季风强度变化对气溶胶分布的影响。基于MODIS/AOD,发现近10年东亚地区冬季AOD呈现上升趋势,最大值为2007年的0.44,高值区覆盖四川盆地、华北平原及长江中下游大部分地区。风场特征类冬季风指数分析表明,东亚冬季风存在明显的年际和年代际差异,近年出现逐渐减弱的趋势。强冬季风年,海陆气压差增大、东亚大槽加深增强,东亚地区偏北风异常,风场的增强将引导更多冷空气南下,从而给东亚大部分地区带来明显的降温天气;弱年相反。气象场差异引起气溶胶分布变化,强年较强的偏北风将气溶胶向南方输送,东亚地区AOD出现“北低南高”的空间分布;弱年偏北风较弱,导致气溶胶集中在华北平原一带,AOD出现“北高南低”的空间分布。