Precursory atmospheric teleconnection patterns for strong Siberian High events

本文利用日本55年逐日再分析资料,发现在SH异常增强前,有三种不同的大气遥相关型前兆信号,即斯堪的纳维亚(SCA)型,西太平洋(WP)型,极地-欧亚(POL)型据此,本文将异常增强的SH分为对应的三类事件.合成结果表明,三类事件在典型环流特征和对东亚气温的影响上存在着明显的不同.具体而言,SCA类事件主要表现为在欧亚中高纬度上自西向东的波列异常,WP类事件表现为环流异常自下游太平洋/俄罗斯远东地区向西发展的特征,POL型事件的显著信号则来源于自极区向南移动的反气旋式环流异常.在对东亚地表气温的影响上,SCA类与POL类事件类似,它们均可造成大范围的低温异常.而WP类仅在我国北方和东部地区造成强度较弱的地表气温异常,但该异常的持续性特征较明显。

Teleconnection between Sea Ice in the Barents Sea in June and the Silk Road,Pacific–Japan and East Asian Rainfall Patterns in August

In contrast to previous studies that have tended to focus on the influence of the total Arctic sea-ice cover on the East Asian summer tripole rainfall pattern, the present study identifies the Barents Sea as the key region where the June sea-ice variability exerts the most significant impacts on the East Asian August tripole rainfall pattern, and explores the teleconnection mechanisms involved. The results reveal that a reduction in June sea ice excites anomalous upward air motion due to strong near-surface thermal forcing, which further triggers a meridional overturning wave-like pattern extending to midlatitudes.Anomalous downward motion therefore forms over the Caspian Sea, which in turn induces zonally oriented overturning circulation along the subtropical jet stream, exhibiting the east–west Rossby wave train known as the Silk Road pattern. It is suggested that the Bonin high, a subtropical anticyclone predominant near South Korea, shows a significant anomaly due to the eastward extension of the Silk Road pattern to East Asia. As a possible descending branch of the Hadley cell, the Bonin high anomaly ultimately triggers a meridional overturning, establishing the Pacific–Japan pattern. This in turn induces an anomalous anticyclone and cyclone pair over East Asia, and a tripole vertical convection anomaly meridionally oriented over East Asia. Consequently, a tripole rainfall anomaly pattern is observed over East Asia. Results from numerical experiments using version 5 of the Community Atmosphere Model support the interpretation of this chain of events.

The Linkage between the Pacific-North American Teleconnection Pattern and the North Atlantic Oscillation

In this study, using the ECMWF reanalysis data, the possible linkage between the Pacific-North American teleconnection pattern （PNA） and the North Atlantic Oscillation （NAO） during boreal winter （December- February） is investigated. The PNA and the NAO pattern are obtained by performing Rotated Empirical Orthogonal Function （REOF） analysis on an anomalous daily mean 300-hPa geopotential height field. The composite daily NAO indices show that the NAO indices are prone to be negative （positive） when the contemporary PNA indices are extremely positive （negative）. The correlation coefficients between the daily PNA and NAO indices also confirm that, indeed, there is a significant anti-correlation between the PNA and NAO indices. The correlation peaks at a lag of 0 days （meaning contemporary correlation）, and its value is 0.202. Analyses of a newly defined Rossby wave breaking index and diagnostics of the stream function tendency equation indicate that the anti-correlation between PNA and NAO may be caused by the anomalous Rossby wave breaking events associated with the PNA pattern.

Studies on the Northern Early Summer Teleconnection Patterns, Their Interannual Variations and Relation to Drought / Flood in China

By using the one-point correlation method, calculations have been made of the northern early summer 500 hPa teleconnection patterns. Seven teleconnection patterns are revealed, namely, the Western Atlantic (WA), the Eastern Atlantic (EA), the Eurasian (EU), the Bengal / Northern Pacific (BNP), the Western Pacific (WP), the East Asian / Pacific (EAP), and the Huanghe / East Asian (HEA) patterns. Their centers are determined and their yearly intensity indices (1951-1990) are calculated. On this basis the relationship between their interannual variations and the drought / flood in China is examined. It is noted that the EU, HEA and EAP wave trains are closely related to the drought / flood in China. The HEA and EAP patterns strongly influence the precipitation in eastern China. For example, the fierce floods experienced in 1991 early summer over China are related to the weak EAP and strong HEA patterns.

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. Int particular, more studies should focus on the teleconnection patterns over extratropical Eurasia.

Possible connection between anomalous activity of Scandinavian Atmospheric Teleconnection Pattern and winter snowfall in the Yangtze-Huaihe River Basin of China

The temporal and spatial characteristics of winter snowfall in the Yangtze–Huaihe River Basin (YHRB) of China and its possible connection with Scandinavian Atmospheric Teleconnection Pattern (SCAND) anomalies are explored based on daily meteorological data contained in the Daily Surface Climate Dataset for China (V3.0) during the period 1960–2012. Results show that winter snowfall in the YHRB exhibits consistent anomalies over the whole region for the interannual variation during 1960–2012. Further analysis suggests that winter snowfall anomalies in the YHRB are closely linked to the anomalous wintertime SCAND activity. When there is more winter snowfall in the YHRB, SCAND is usually in a positive phase, accompanied by a strengthened Urals blocking high and East Asian trough, which is conducive to strengthened cold-air activity, intensified vertical motions, and more water vapor transport in the YHRB. In contrast, less winter snowfall in the YHRB usually happens in the negative phase of SCAND. Our results provide useful information to better understand the relevant mechanism responsible for anomalous winter snowfall in this area.

Multi-scale regionalization based mining of spatio-temporal teleconnection patterns between anomalous sea and land climate events

Climate sequences can be applied to defining sensitive climate zones, and then the mining of spatio-temporal teleconnection patterns is useful for learning from the past and preparing for the future. However, scale-dependency in this kind of pattern is still not well handled by existing work. Therefore, in this study, the multi-scale regionalization is embedded into the spatio-temporal teleconnection pattern mining between anomalous sea and land climatic events. A modified scale-space clustering algorithm is first developed to group climate sequences into multi-scale climate zones. Then, scale variance analysis method is employed to identify climate zones at characteristic scales, indicating the main characteristics of geographical phenomena. Finally, by using the climate zones identified at characteristic scales, a time association rule mining algorithm based on sliding time windows is employed to discover spatio-temporal teleconnection patterns. Experiments on sea surface temperature, sea level pressure, land precipitation and land temperature datasets show that many patterns obtained by the multi-scale approach are coincident with prior knowledge, indicating that this method is effective and reasonable. In addition, some unknown teleconnection patterns discovered from the multi-scale approach can be further used to guide the prediction of land climate.

Teleconnection Patterns in the Northern Hemisphere Simulated by IAP GCM

Based on monthly mean sea level pressure and 500 hPa height data for a 20-year period simulated by IAP 2L AGCM, teleconnection patterns in the Northern Hemisphere appearing in the model are identified and compared with observations. The results show that almost all of the observed teleconnection patterns in the Northern winter can be reproduced by the model, thus these patterns exist in the atmosphere without any external anomalies. On the other hand, the simulated teleconnection patterns are more dependent on each other than the observed, i.e., they are lack of spatial orthogonality among them, therefore, it is possible that more complex patterns will appear under the action of anomalous external factors. Besides, the simulated teleconnection patterns in summer are greatly different from those in winter, in particular, its scale in summer is much less than that in winter.

Summertime Atmospheric Teleconnection Pattern Associated with a Warming over the Eastern Tibetan Plateau

By using a surface air temperature index （SATI） averaged over the eastern Tibetan Plateau （TP）, investigation is conducted on the short-term climate variation associated with the interannual air warming （or cooling） over the TP in each summer month. Evidence suggests that the SATI is associated with a consistent teleconnection pattern extending from the TP to central-western Asia and southeastern Europe. Associated rainfall changes include, for a warming case, a drought in northern India in May and June, and a stronger mei-yu front in June. The latter is due to an intensified upper-level northeasterly in eastern China and a wetter and warmer condition over the eastern TP. In the East Asian regions, the time-space distributions of the correlation patterns between SATI and rainfall are more complex and exhibit large differences from month to month. Some studies have revealed a close relationship between the anomalous heating over the TP and the rainfall anomaly along the Yangtze River valley appearing in the summer on a seasonal mean time-scale, whereas in the present study, this relationship only appears in June and the signal＇s significance becomes weaker after the long-term trend in the data was excluded. Close correlations between SATI and the convection activity and SST also occur in the western Pacific in July and August： A zonally-elongated warm tone in the SST in the northwestern Pacific seems to be a passive response of the associated circulation related to a warm SATI. The SATI-associated teleconnection pattern provides a scenario consistently linking the broad summer rainfall anomalies in Europe, central-western Asia, India, and East Asia.

Internal Dynamics of the Generation of Atmospheric Teleconnection Patterns

A preferred growing perturbation concept has been introduced into the dynamical study on the generation ofatmospheric teleconnection patterns.It is shown that all the important teleconnection patterns observed in the realatmosphere may be established through internal barotropic dynamical processes.

Connections between the Eurasian Teleconnection and Concurrent Variation of Upper-level Jets over East Asia

The variation of the East Asian jet stream （EAJS） associated with the Eurasian （EU） teleconnection pattern is investigated using 60-yr NCEP-NCAR daily reanalysis data over the period 1951-2010.The EAJS consists of three components：the polar front jet （PFJ）; the plateau subtropical jet （PSJ）; and the ocean subtropical jet （OSJ）.Of these three jets over East Asia,the EU pattern exhibits a significant influence on the PFJ and OSJ.There is a simultaneous negative correlation between the EU pattern and the PFJ.A significant positive correlation is found between the EU pattern and the OSJ when the EU pattern leads the OSJ by about 5 days.There is no obvious correlation between the EU pattern and the PSJ.The positive EU phase is accompanied by a weakened and poleward-shifted PFJ,which coincides with an intensified OSJ.A possible mechanism for the variation of the EAJS during different EU phases is explored via analyzing the effects of 10-day high-and low-frequency eddy forcing.The zonal wind tendency due to high-frequency eddy forcing contributes to the simultaneous negative correlation between the EU pattern and the PFJ,as well as the northward/southward shift of the PFJ.High-and low-frequency eddy forcing are both responsible for the positive correlation between the EU pattern and the OSJ,but only high-frequency eddy forcing contributes to the lagged variation of the OSJ relative to the EU pattern.The negative correlation between the EU pattern and winter temperature and precipitation anomalies in China is maintained only when the PFJ and OSJ are out of phase with each other.Thus,the EAJS plays an important role in transmitting the EU signal to winter temperature and precipitation anomalies in China.

Greenland Ice Sheet Elevation Change in Winter and Influence of Atmospheric Teleconnections in the Northern Hemisphere

The relationship between the variability of the surface elevation of the Greenland Ice Sheet (GIS) in winter and sea level pressure is identified through analysis of data from satellite-borne radar altimeters, together with meteorological data fields during 1993 2005. We found that both the North Pacific Oscillation (NPO) and the North Atlantic Oscillation (NAO), the two major teleconnection patterns of the atmospheric surface pressure fields in the Northern Hemisphere, significantly influence the GIS winter elevation change. Further, it is suggested that the NPO may affect the GIS accumulation by influencing the NAO, particularly by changing the intensity and location of the Icelandic Low.

TELECONNECTION BETWEEN SEA－SURFACE TEMPERATURE IN TROPICAL EASTERN PACIFIC AND OZONOSPHERE OVER NORTHERN HEMISPHERE

Seasonal interaction between sea-surface temperature (SST) in the tropical eastern Pacific and ozone layer in Northern Hemisphere, ahd the layer,s teleconnection spatial structure caused by SST effeets, for January and July, are statistically analysed. The result indicates that the areas spacially correlated between SST and ozone layer in January greatly differ from the ones in July and they show opposite tendency in the signs of correlation, so do the teleconnection pattern for the ozone lay6r due to effects of SST in different seasons. In addition, persistent' influence of SST on the ozone layer results insuperposition of seasonal SST effects on the layer and makes it characteristic of well-defined wavetrainsin responses to SST. It is concluded that SST in the tropical eastern Pacific is of great importance to thenorthern ozone layer distribution and its seasonal evolution.

Linkage Between European and East Asian Heatwaves on Synoptic Scales

Concurrent extreme weather events in geographically distant areas potentially cause high-end risks for societies.By using network analysis,the present study managed to identify significant nearly-simultaneous occurrences of heatwaves between the grid cells in East Asia and Eastern Europe,even though they are geographically far away from each other.By further composite analysis,this study revealed that hot events first occurred in Eastern Europe,typically with a time lag of3-4 days before the East Asian heatwave events.An eastward propagating atmospheric wave train,known as the circumglobal teleconnection(CGT)pattern,bridged the sequent occurrences of extreme events in these two remote regions.Atmospheric blockings,amplified by surface warming over Eastern Europe,not only enhanced local heat extremes but also excited a CGT-like pattern characterized by alternative anomalies of high and low pressures.Subsequent downstream anticyclones in the middle and upper troposphere reduced local cloud cover and increased downward solar radiation,thereby facilitating the formation of heatwaves over East Asia.Nearly half of East Asian heatwave events were preceded by Eastern European heatwave events in the 10-day time range before East Asian heatwave events.This investigation of heatwave teleconnection in the two distant regions exhibits strong potential to improve the prediction accuracy of East Asian heatwaves.

两类厄尔尼诺事件对次年山东夏季降水的影响研究

厄尔尼诺(El Nino)事件可根据海温极大值中心分为东部型El Nino和中部型El Nino。本研究通过观测资料研究了1979-2020年两类El Nino事件对次年山东夏季(6-8月)季节平均和月平均降水异常的影响。结果显示,中部型El Nino次年夏季西北太平洋反气旋较气候态偏北,进而增强东亚夏季风,使得山东夏季平均降水偏多。伴随着反气旋在季节内的北移,降水正异常在晚夏(8月)最为显著,而东部型El Nino次年夏季反气旋较气候态偏南偏弱。同期日本列岛地区由于东亚-太平洋遥相关负位相的出现产生异常气旋,山东地区受气旋西侧干冷北风控制,夏季降水偏少。由于气旋强度在季节内逐渐降低,所以山东干旱在初夏(6月)最显著。这些结果可以为未来山东夏季降水季节预测提供重要参考。

Tropical Cyclones over the Western North Pacific Strengthen the East Asia–Pacific Pattern during Summer

The contribution of tropical cyclones(TCs)to the East Asia–Pacific(EAP)teleconnection pattern during summer was investigated using the best track data of the Joint Typhoon Warning Center and NCEP-2 reanalysis datasets from 1979 to2018.The results showed that the TCs over the western North Pacific(WNP)correspond to a strengthened EAP pattern:During the summers of strong convection over the tropical WNP,TC days correspond to a stronger cyclonic circulation anomaly over the WNP in the lower troposphere,an enhanced seesaw pattern of negative and positive geopotential height anomalies over the subtropical WNP and midlatitude East Asia in the middle troposphere,and a more northward shift of the East Asian westerly jet in the upper troposphere.Further analyses indicated that two types of TCs with distinctly different tracks,i.e.,westward-moving TCs and northward-moving TCs,both favor the EAP pattern.The present results imply that TCs over the WNP,as extreme weather,can contribute significantly to summer-mean climate anomalies over the WNP and East Asia.

Year aridity index patterns in northwest China and the relationship to summer North Atlantic sea surface temperature

Aim to linking the variability of drought in northwest China to the oceanic influence of North Atlantic SSTs at the background of global warming and at the regional climate change shifting stages, year aridity index variations in northwest China and summer North Atlantic sea surface temperature （SST） variations are examined for the 44 a period of 1961-2004 using singular value decomposition （SVD） analysis. Results show that the SST anomalies （SSTA）in the North Atlantic in summer reflected three basic models. The first SVD mode of SST pattern shows a dipole - like variation with the positive center located at southwest and negative center at northeast of extratropical North Atlantic. And it strongly relates to the positive trend in AI variation in northwest China. The second coupled modes display the coherent positive anomalies in extratropical North Atlantic SST and the marked opposite trend of AI variability between north and south of Xinjiang. In addition, the lag correlation analysis of the first mode of SSTA and geopotential heights at 500 hPa variations also shows that the indication of the former influencing the latter configuration, which result in higher air temperature and less precipitation when the SSTA in the North Atlantic Ocean in summer motivated Eurasian circulation of EA pattern, further to influence the wet - dry variations in northwest China by the ocean-to - atmosphere forcing.

2022年夏季中国高温的环流异常特征

基于美国国家海洋和大气管理局(National Oceanic and Atmospheric Administration, NOAA)全球范围扩展重建海面温度资料第5版本(Extended Reconstructed Sea Surface Temperature version 5,ERSSTv5),以及美国国家环境预报中心和国家大气研究中心NCEP(National Centers for Environmental Prediction)/NCAR(National Center for Atmospheric Research)逐月全球再分析资料,采用相关、回归、合成及物理量诊断等方法,对2022年夏季中国大范围高温相关环流异常的可能成因进行了分析。结果表明:(1)2022年夏季南亚高压偏强并分别向东、西方向扩展,西太平洋副热带高压(以下简称“副高”)异常偏强西伸。2022夏季为拉尼娜(La Nina)年,但热带大西洋垂直上升环流相对西太平洋更强,且热带印度洋到西太平洋热带垂直上升环流异常也偏强。(2)2022年热带大西洋、印度洋到西太平洋上空垂直环流异常和La Nina共同作用,使得夏季南亚高压和西太平洋副高极端异常。La Nina和印度洋到西太平洋垂直环流异常有利于南亚高压和西太平洋副高的偏强西伸;热带大西洋环流异常则既有利于南亚高压的加强及东扩,也有利于西太平洋副高偏强西伸。(3)印度洋到西太平洋垂直环流主要通过局地经向哈得来(Hadley)环流影响青藏高原到中国东部的环流异常,表现为青藏高原到中国东部中低层为显著的辐散异常;热带大西洋则通过引起纬向风异常(急流异常),激发遥相关波列并向下游传播,进而影响青藏高原到中国东部地区的环流异常。

春季东大西洋/西俄罗斯遥相关型异常与我国气温异常的联系

利用1979—2017年逐月中国160站气温资料和美国NCEP-DOE再分析资料,研究了春季东大西洋/西俄罗斯(East Atlantic/West Russia,EATL/WRUS)遥相关型异常与我国气温异常的联系,并初步探讨了这一联系的可能物理机制。研究结果表明,春季EATL/WRUS遥相关型正(负)位相表现为北大西洋至欧亚大陆中高纬地区的500 hPa位势高度场“+-+”(“-+-”)纬向波列,该波列的三个主要活动中心分别位于西欧、乌拉尔山附近和贝加尔湖南侧。在垂直方向上,春季EATL/WRUS遥相关型具有明显的相当正压结构。春季EATL/WRUS遥相关型异常与我国西北地区春季气温异常具有显著的正相关关系。当春季EATL/WRUS遥相关型处于正(负)位相年,乌拉尔山附近地区为负(正)位势高度异常和气旋性(反气旋性)环流异常,贝加尔湖南侧地区出现正(负)位势高度异常和反气旋性(气旋性)环流异常,使得影响我国西北地区的冷空气减弱(加强),从而导致我国西北地区春季气温异常升高(降低)。

北大西洋-东亚和北亚型遥相关的机制及其对新疆夏季旱涝的影响

北大西洋-东亚和北亚(简称NAENA)型遥相关是夏季欧亚大陆对流层上层经向风异常的第二主导模态,对欧亚大陆多尺度气候变率有显著影响。本文在分析NAENA型维持的动力学机制的基础上,研究了该遥相关型对新疆夏季旱涝异常的影响及其可能机制。大气波列的涡度收支分析表明,气候态的旋转纬向风引起的扰动涡度平流可以被扰动旋转经向风引起的平均涡度平流所补偿。能量转换过程分析表明,该大气波列有效地从平均流中提取有效位能,通过斜压能量转换过程得以维持。大西洋海温异常三极子模态则是NAENA型维持的重要外强迫因子。回归分析表明NAENA型遥相关能通过促进南疆夏季降水,显著影响新疆的旱涝异常。NAENA型位于中亚的气旋性低压一方面增强了南疆地区的垂直上升运动,同时气旋性环流将更多的水汽输送到该地区,有利于水汽在对流层中低层的异常辐合,进而对南疆的降水有促进作用。