An Inter-hemispheric Teleconnection and a Possible Mechanism for Its Formation

Through observational analyses,an inter-hemispheric teleconnection is identified between the subtropical region of the South China Sea to the western Pacific near the Philippines(WP)and the region to the east of Australia(AE).The teleconnection is significantly correlated with sea surface temperature anomalies(SSTAs)in key sea areas(including the Indian Ocean,the South China Sea,and the area to the east of Australia).Based on the IAP T42L9 model,numerical experiments are performed to explore a possible mechanism for the formation of the teleconnection.The results show that the positive SST anomalies in the key sea areas may jointly contribute to the occurrence and maintenance of the positive geopotential height anomalies over both the WP and AE and be a critical factor in the teleconnection formation.The large-scale SST anomaly in the Indian Ocean,involving the tropics and subtropics of both hemispheres,may lead to concurrent atmospheric responses over both the WP and AE,while the effect of the local SST anomaly to the east of Australia seems to reinforce and maintain the positive height anomaly over the AE.     

A study of the contribution of mass elevation effect to the altitudinal distribution of timberline in the Northern Hemisphere简

Alpine timberline, as the ＂ecologica tion of scientists in many fields, especially in transition zone,＂ has long attracted the atten- recent years. Many unitary and dibasic fitting models have been developed to explore the relationship between timberline elevation and latitude or temperature. However, these models are usually on regional scale and could not be applied to other regions; on the other hand, hemispherical-scale and continental-scale models are usually based on about 100 timberline data and are necessarily low in precision. The present article collects 516 data sites of timberline, and takes latitude, continentality and mass elevation effect （MEE） as independent variables and timberline elevation as dependent variable to develop a ternary linear regression meteorological data released by WorldClim and model. Continentality is calculated using the mountain base elevation （as a proxy of mass elevation effect） is extracted on the basis of SRTM 90-meter resolution elevation data. The results show that the coefficient of determination （R2） of the linear model is as high as 0.904, and that the contribution rate of latitude, continentality and MEE to timberline elevation is 45.02% （p=0.000）, 6.04% （p=0.000） and 48.94% （p=0.000）, respectively. This means that MEE is simply the primary factor contributing to the elevation distribution of timberline on the continental and hemispherical scales. The contribution rate of MEE to timberline altitude dif- fers in different regions, e.g., 50.49% （p=0.000） in North America, 48.73% （p=0.000） in the eastern Eurasia, and 43.6% （p=0.000） in the western Eurasia, but it is usually very high.     

大气环流异常对山东雨季降水的影响

利用1958～2003年NCEP/NCAR再分析资料,对山东旱涝年500hPa高度距平、高(200hPa)低(925hPa)层散度距平、OLR距平分布以及115～123°E山东东西边界范围内的平均垂直速度进行合成分析,并与华北旱涝年大气环流的分布特征进行了对比。结果发现:(1)北半球500hPa夏季存在的东亚-太平洋遥相关型(EAP)对山东夏季降水产生重要影响,山东涝年夏季500hPa呈现出EAP型,旱年呈负EAP型。(2)山东涝年,鄂霍茨克海高压春季偏强、夏季偏弱,山东上游易维持低压槽区,副高偏北,热带地区对流活动加强,Hadley和Walker环流加强,山东上空盛行上升运动。旱年与涝年的特征基本相反,只是鄂霍茨克海高压在春季和夏季均较常年偏强。(3)不同旱年(涝年)的500hPa特征与旱年(涝年)平均情况相似,只是有时距平中心位置和强度不同。特别是涝年,冷空气强度、入侵路径以及副高的位置均有差别。(4)华北旱涝年500hPa高度距平与山东不同。华北旱年500hPa欧亚大陆中高纬度呈现出EU遥相关分布,且华北涝年夏季鄂霍茨克海和朝鲜-日本地区位势高度变化不显著。(5)影响山东夏季降水的热带强迫源区主要位于热带印度洋、南海-热带西太平洋,两者实现遥相关的可能机制是热带强迫所激发的大尺度准定常Rossby波列的传播。     

月内尺度南半球环状模对应的大气环流异常传播特征

本文利用NCEP/NCAR逐日再分析资料, 分析了南半球环状模 (Southern Hemisphere Annular Mode, 简称SAM) 在月内时间尺度 (sub-monthly timescales, 5～30天)上相关环流的垂直和水平传播特征。结果表明, 月内SAM对应的纬向风异常和温度异常具有明显自南极地区向南半球中纬度地区水平传播特征; 在垂直方向上, 纬向风异常为明显上传特征, 温度异常则具有在极地和高纬度地区明显上升、低纬度地区下沉的特点。月内SAM对应的南半球中高纬度地区上传信号表明, 在较短的月内时间尺度上, 对流层信号可以突破对流层顶, 上传达到平流层; 而月内SAM对应的整层南传信号表明, 南极地区环流变化超前于中高纬度地区, 因此在1～3周的月内时间尺度上, 极区信号可能对中高纬地区信号具有指示意义。     

Pathways of Influence of the Northern Hemisphere Mid–high Latitudes on East Asian Climate: A Review

This paper reviews recent progress made by Chinese scientists on the pathways of influence of the Northern Hemisphere mid–high latitudes on East Asian climate within the framework of a "coupled oceanic–atmospheric(land–atmospheric or seaice–atmospheric) bridge" and "chain coupled bridge". Four major categories of pathways are concentrated upon, as follows:Pathway A—from North Atlantic to East Asia; Pathway B—from the North Pacific to East Asia; Pathway C—from the Arctic to East Asia; and Pathway D—the synergistic effects of the mid–high latitudes and tropics. In addition, definitions of the terms "combined effect", "synergistic effect" and "antagonistic effect" of two or more factors of influence or processes and their criteria are introduced, so as to objectively investigate those effects in future research.     

2000年北半球平流层、对流层质量交换的季节变化

用2000年NCEP资料,P坐标下Wei公式诊断北半球平流层、对流层交换的季节变化.主要结论:(1)热带西太平洋是物质由对流层向平流层输送的主要通道,并有明显的季节性东西移动.由于2000年赤道辐合带偏弱,因此秋季通量最大.(2)中高纬度地区同时存在向上、向下的通量,大尺度槽区伴随着平流层向下的输送.一年中冬春季向下的输送强,夏秋季较弱,其季节变化与大尺度环流的季节性变化一致.(3)东亚地区存在很强的平流层向下输送,且中心位置移动不大.只占北半球5.6%面积的东亚其年净交换量竟占北半球的29%,这说明东亚地区的平流层与对流层之间的质量交换对北半球平流层、对流层交换研究的重要性.     

平流层强、弱极涡事件的演变过程及其对我国冬季天气的影响

本文利用1979～2010年的NCEP再分析资料,通过北半球环状模NAM指数挑选出的强、弱极涡个例,分析了北半球平流层异常变化过程中行星波的演变以及与之相联系的我国天气的变化特征。结果表明,在强极涡事件前,行星波1波会被反射回对流层,极地波导减弱,低纬波导增强,中高纬地区的E-P通量矢量有着从平流层传播到对流层的趋势;强极涡事件后,极地波导增强,低纬波导减弱。在弱极涡事件前,中、高纬度行星波1波沿着极地波导的传播明显增强;弱极涡事件后,极地波导明显减弱。与此对应的我国天气也有明显变化,在强极涡事件前,我国大部分地区温度偏低,南方地区偏湿而新疆西北部和云南西部地区偏干;在强极涡事件后,东亚冬季风进一步增强,冷空气加强南下,南方地区可降水量减少,新疆西北部仍然偏干,而云南大部分地区可将水量增加。在弱极涡事件前,东亚冬季风显著增强,使我国气温偏冷,降水减少,而弱极涡事件后,我国气温明显回升,中、东部地区和新疆西北部地区降水明显增加。     

100 hPa极涡、南亚高压的变化及大气环流分布特征

利用NCEP/NCAR高度场资料进行计算,对冬、夏极涡与南亚高压面积进行Morlet小波变换,并对100 hPa高度场进行EOF分解和长期趋势分析.结果表明:极涡、南亚高压具有相似的演变特征,这种相似特征在前期冬季极涡与南亚高压之间表现更为明显,体现了准5年尺度和准20年尺度的周期变化,在变化的位相上则相反.EOF分析表明,前期冬季高纬度地区与中低纬度地区的环流变化呈相反趋势,且第一模态的时间系数与前期冬季极涡的趋势一致,第一模态在一定程度上反映了前期冬季大气环流分布.夏季第一模态全场为负值,体现了夏季100 hPa整体异常性;第二模态反映了副热带中低纬度大气环流与高纬度大气环流变化相反.从其长期变化趋势来看,冬季高纬度地区的高度场呈负趋势变化,副热带地区呈正趋势变化,夏季除我国华北部分地区为负趋势变化外,均为正趋势变化.极涡、南亚高压的这种年代际变化与100 hPa高度场的长期线性趋势变化有关.     

Boreal winter rainfall anomaly over the tropical indo-pacific and its effect on northern hemisphere atmospheric circulation in CMIP5 models

Experimental outputs of 11 Atmospheric Model Intercomparison Project （AMIP） models from phase 5 of the Coupled Model Intercomparison Project （CMIP5） are analyzed to assess the atmospheric circulation anomaly over Northern Hemisphere induced by the anomalous rainfall over tropical Pacific and Indian Ocean during boreal winter.The analysis shows that the main features of the interannual variation of tropical rainfall anomalies,especially over the Central Pacific （CP） （5°S-5°N,175°E-135°W） and Indo-western Pacific （IWP） （20°S-20°N,110°-150°E） are well captured in all the CMIP5/AMIP models.For the IWP and western Indian Ocean （WIO） （10°S-10°N,45°-75°E）,the anomalous rainfall is weaker in the 11 CMIP5/AMIP models than in the observation.During El Ni（n）o/La Ni（n）a mature phases in boreal winter,consistent with observations,there are geopotential height anomalies known as the Pacific North American （PNA） pattern and Indo-western Pacific and East Asia （IWPEA） pattern in the upper troposphere,and the northwestern Pacific anticyclone （cyclone） （NWPA） in the lower troposphere in the models.Comparison between the models and observations shows that the ability to simulate the PNA and NWPA pattern depends on the ability to simulate the anomalous rainfall over the CP,while the ability to simulate the IWPEA pattern is related to the ability to simulate the rainfall anomaly in the IWP and WIO,as the SST anomaly is same in AMIP experiments.It is found that the tropical rainfall anomaly is important in modeling the impact of the tropical Indo-Pacific Ocean on the extratropical atmospheric circulation anomaly.