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1.
The summer snow anomalies over the Tibetan Plateau （TP） and their effects on climate variability are often overlooked,possibly due to the fact that some datasets cannot properly capture summer snow cover over high terrain.The satellite-derived Equal-Area Scalable Earth grid （EASE-grid） dataset shows that snow still exists in summer in the western part and along the southem flank of the TP.Analysis demonstrates that the summer snow cover area proportion （SCAP） over the TP has a significant positive correlation with simultaneous precipitation over the mei-yu-baiu （MB） region on the interannual time scale.The close relationship between the summer SCAP and summer precipitation over the MB region could not be simply considered as a simultaneous response to the Silk Road pattern and the SST anomalies in the tropical Indian Ocean and tropical central-eastern Pacific.The SCAP anomaly has an independent effect and may directly modulate the land surface heating and,consequently,vertical motion over the western TP,and concurrently induce anomalous vertical motion over the North Indian Ocean via a meridional vertical circulation.Through a zonal vertical circulation over the tropics and a Kelvin wave-type response,anomalous vertical motion over the North Indian Ocean may result in an anomalous high over the western North Pacific and modulate the convective activity in the western Pacific warm pool,which stimulates the East Asia-Pacific （EAP） pattern and eventually affects summer precipitation over the MB region.  相似文献   

2.
基于1960—2019年中国东北地区108个台站逐日降水资料、JRA-55再分析资料和Hadley中心海温数据,分析了东北地区春季极端连续无雨日的年际变化特征及其与前冬北太平洋地区大气环流和海表温度的关系。研究表明,东北地区春季极端连续无雨日集中在3—4月。当3—4月极端连续无雨日偏多时,贝加尔湖地区存在异常高压,东北地区受偏北气流影响,局地水汽辐散。进一步分析发现,东北地区3—4月极端连续无雨日与前冬1—2月北太平洋地区偶极型海平面气压存在密切联系。该大气模态可以引起同期北太平洋海温呈现出马蹄形异常分布并持续到3—4月。在3—4月,海温异常可以通过改变北太平洋上空的经向温度梯度,引起东亚到北太平洋地区的西风变化,进而有利于贝加尔湖地区出现异常高压。另一方面,海温异常还会增强北半球中纬度的波列活动,东传的波列也可以增强贝加尔湖地区的高压。上述异常环流为东北地区极端连续无雨日的增加提供了有利背景条件。留一交叉验证结果显示,前冬1—2月北太平洋地区偶极型海平面气压可作为东北春季极端连续无雨日的潜在预测因子。  相似文献   

3.
The variability of climate in the lee side of the Tibetan Plateau (TP) often exhibits unique features. In this study, the authors investigate the variations of early autumn rainfall in the lee side of the TP (LSTP). The rainfall amount and number of rain days in LSTP increase from August to September. The center of heavy and torrential rains during September is located in LSTP as well. These unique features are attributed to later withdrawal of the East Asian summer monsoon in the middle and higher troposphere compared to the lower troposphere and stronger South Asian summer monsoon and thermal forcing of the TP. The September rainfall in LSTP experienced strong interdecadal fluctuation, with overall below normal rainfall from mid-1980s to late 2000s, while there was no apparent long-term trend in the August and October rainfall amount. The above normal September rainfall is associated with an anomalous anticyclone over the western North Pacific, a weaker-than-normal ridge around the Lake Baikal, a stronger-than-normal East Asian jet stream, and warmer air over the southeastern TP. The interdecadal decrease in rainfall in September may be caused by the central equatorial Pacific warming, which induces an anomalous cyclone over the western North Pacific. The September anomalous cyclone is stronger and more westward compared to that in August and October, and thus favors the below normal rainfall in LSTP.  相似文献   

4.
We investigate European summer (July–August) precipitation variability and its global teleconnections using the NCEP/NCAR reanalysis data (1950–2010) and a historical Coupled Model Intercomparison Project climate simulation (1901–2005) carried out using the ECHAM6/MPIOM climate model. A wavelike pattern is found in the upper tropospheric levels (200 hPa) similar to the summer circumglobal wave train (CGT) extending from the North Pacific to the Eurasian region. The positive phase of the CGT is associated with upper level anomalous low (high) pressure over western (eastern) Europe. It is further associated with a dipole-like precipitation pattern over Europe entailing significantly enhanced (reduced) precipitation over the western (eastern) region. The anomalous circulation features and associated summer precipitation pattern over Europe inverts for the negative CGT phase. Accordingly, the global teleconnection pattern of a precipitation index summarizing summer precipitation over Western Europe entails an upper level signature which consists of a CGT-like wave pattern extending from the North Pacific to Eurasia. The imprint of the CGT on European summer precipitation is distinct from that of the summer North Atlantic Oscillation, despite the two modes of variability bear strong similarities in their upper level atmospheric pattern over Western Europe. The analysis of simulated CGT features and of its climatic implications for the European region substantiates the existence of the CGT-European summer precipitation connection. The summer CGT in the mid-latitude therefore adds to the list of the modes of large-scale atmospheric variability significantly influencing European summer precipitation variability.  相似文献   

5.
The features of large-scale circulation, storm tracks and the dynamical relationship between them were examined by investigating Rossby wave breaking （RWB） processes associated with Eastern Pacific （EP） and Central Pacific （CP） E1-Nifio. During EP E1-Nino, the geopotential height anomaly at 500 hPa （Z500） exhibits a Pacific-North America （PNA） pattern. During CP EI-Nifio, the Z500 anomaly shows a north positive-south negative pattern over the North Pacific. The anomalous distributions of baroclinicity and storm track are consistent with those of upper-level zonal wind for both EP and CP EI-Nino, suggesting impacts of mean flow on storm track variability. Anticyclonic wave breaking （AWB） oczurs less frequently in EP EI-Nino years, while cyclonic wave breaking （CWB） occurs more frequently in CP EI-Nino years over the North Pacific sector. Outside the North Pacific, more CWB events occur over North America during EP Ei-NiNo. When AWB events occur less frequently over the North Pacific during EP EI-Nino, Z500 decreases locally and the zonal wind is strengthened （weakened） to the south （north）. This is because AWB events reflect a monopoie high anomaly at the centroid of breaking events. When CWB events occur more frequently over the North Pacific under CP EI-Nino conditions, and over North America under EP EI-Nino condition, Z500 increases （decreases） to the northeast （southwest）, since CWB events are related to a northeast-southwest dipole Z500 anomaly. The anomalous RWB events act to invigorate and reinforce the circulation anomalies over the North Pacific-North America region linked with the two types of EI-Nino.  相似文献   

6.
Extreme precipitation events in the upper Yangtze River Valley (YRV) have recently become an increasingly important focus in China because they often cause droughts and floods. Unfortunately, little is known about the climate processes responsible for these events. This paper investigates factors favorable to frequent extreme precipitation events in the upper YRV. Our results reveal that a weakened South China Sea summer monsoon trough, intensified Eurasian-Pacific blocking highs, an intensified South Asian High, a southward subtropical westerly jet and an intensified Western North Pacific Subtropical High (WNPSH) increase atmospheric instability and enhance the convergence of moisture over the upper YRV, which result in more extreme precipitation events. The snow depth over the eastern Tibetan Plateau (TP) in winter and sea surface temperature anomalies (SSTAs) over three key regions in summer are important external forcing factors in the atmospheric circulation anomalies. Deep snow on the Tibetan Plateau in winter can weaken the subsequent East Asian summer monsoon circulation above by increasing the soil moisture content in summer and weakening the land–sea thermal contrast over East Asia. The positive SSTA in the western North Pacific may affect southwestward extension of the WNPSH and the blocking high over northeastern Asia by arousing the East Asian-Pacific pattern. The positive SSTA in the North Atlantic can affect extreme precipitation event frequency in the upper YRV via a wave train pattern along the westerly jet between the North Atlantic and East Asia. A tripolar pattern from west to east over the Indian Ocean can strengthen moisture transport by enhancing Somali cross-equatorial flow.  相似文献   

7.
夏季亚洲—太平洋涛动与大气环流和季风降水   总被引：19，自引：4，他引：15  
利用ERA-40再分析资料和数值模拟,分析了在亚洲-太平洋区域的大气遥相关以及与亚洲季风降水和西北太平洋热带气旋活动气候特征的关系,探讨了青藏高原加热和太平洋海表温度(SST)对遥相关的影响,结果表明:亚洲-太平洋涛动(Asian-Pacific Oscillation,APO)是夏季对流层扰动温度在亚洲与太平洋中纬度之间的一种"跷跷板"现象,当亚洲大陆中纬度对流层偏冷时,中、东太平洋中纬度对流层偏暖,反之亦然;这种遥相关也出现在平流层中,只是其位相与对流层的相反.APO为研究亚洲与太平洋大气环流相互作用提供了一个途径.APO指数也是亚洲-太平洋对流层热力差异指数,它具有年际和年代际的多时间尺度变化特征,在1958-2001年亚洲与太平洋之间的对流层热力差异呈现出减弱趋势,同时也有显著的5.5 a周期.APO形成可能与太阳辐射在亚洲陆地和太平洋的加热差异所造成的纬向垂直环流有关,数值模拟进一步表明:夏季青藏高原加热可以造成高原附近对流层温度升高、上升运动加强,太平洋下沉运动加强、温度下降,从而形成APO现象;而太平洋年代际涛动和赤道东太平洋的厄尔尼若现象对APO的影响可能较小.当夏季APO异常时,南亚高压、欧亚中纬度西风急流、南亚热带东风急流以及太平洋上空的副热带高压都出现显著变化,并伴随着亚洲季风降水及西北太平洋热带气旋活动异常.过去40多年来的长江中上游地区夏季变冷与APO有关,可能是全球大气环流年代际变化在该区域的一种反映.APO异常信号可以传播到南、北两极.此外,亚洲-太平洋之间的这种遥相关型也出现在其他季节.  相似文献   

8.
Based on the National Centers for Environmental Prediction and National Center for Atmospheric Research （NCEP/NCAR） reanalysis data from 1950-1999, interdecadal variability of the East Asian Summer Monsoon （EASM） and its associated atmospheric circulations are investigated. The EASM exhibits a distinct interdecadal variation, with stronger （weaker） summer monsoon maintained from 1950-1964 （1976-1997）. In the former case, there is an enhanced Walker cell in the eastern Pacific and an anti-Walker cell in the western Pacific. The associated ascending motion resides in the central Pacific, which flows eastward and westward in the upper troposphere, descending in the eastern and western ends of the Pacific basin. At the same time, an anomalous East Asian Hadley Cell （EAHC） is found to connect the low-latitude and mid-latitude systems in East Asia, which strengthens the EASM. The descending branch of the EAHC lies in the west part of the anti-Walker cell, flowing northward in the lower troposphere and then ascending at the south of Lake Baikal （40°-50°N, 95°- 115°E） before returning to low latitudes in the upper troposphere, thus strengthening the EASM. The relationship between the EASM and SST in the eastern tropical Pacific is also discussed. A possible mechanism is proposed to link interdecadal variation of the EASM with the eastern tropical Pacific SST. A warmer sea surface temperature anomaly （SSTA） therein induces anomalous ascending motion in the eastern Pacific, resulting in a weaker Walker cell, and at the same time inducing an anomalous Walker cell in the western Pacific and an enhanced EAHC, leading to a weaker EASM. Furthermore, the interdecadal variation of summer precipitation over North China is found to be the south of Lake Baikal through enhancing and reducing strongly regulated by the velocity potential over the regional vertical motions.  相似文献   

9.
Cut-off lows (COLs) are significantly associated with many convective events and anomalous regional climate in the Northeast China. By using 49-year NCEP/NCAR reanalysis data, COL events are detected and tracked by an objective and automatic method based on synoptic concept model. Based on this dataset and daily rain-gauge records in Northeast China during 1979–2005, seasonal climatology of COLs and associated precipitation patterns over Northeast China are investigated. Most COLs have a short lifetime of less than a week and have a spatial size ranging from 500 to 1,000 km, with slight seasonal differences. Temporal variation of COL occurrence exhibits a seasonal cycle, with a peak in summer, and considerable interannual variability. The COLs tend to occur more frequently over the northern Northeast China Plain, and the center for maximum frequency shows a zonal oscillation, with an extension to continent in summer and a shift to western North Pacific coast in winter. Most COLs form to the east of Lake Baikal and decay over the western North Pacific coast. COLs are apt to move along east or southeast passages around the year, and tracks are relatively more complicated in warm seasons. About a quarter of annual mean precipitation over Northeast China is associated with COLs. Moreover, COL-associated precipitation contributes greatly to total precipitation in northern and northwestern parts of Northeast China, and the ratios of COL contribution are stronger during spring and autumn than in summer.  相似文献   

10.
利用近50年月平均的SODA海洋同化资料和NCEP大气再分析资料,研究了热带太平洋次表层海温异常(SOTA)年代际变率主要分布型以及与之相关的亚洲-北太平洋-北美地区上空异常大气环流场,并揭示了类ENSO模态与中国气候异常之间的联系.得到主要结果:(1)热带太平洋SOTA年代际变率有两种类ENSO模态.第一模为类ENSO事件成熟期热带太平洋年代际SOTA状态;第二模为类ENSO过渡期热带太平洋年代际SOTA状态.二者组合构成类ENSO事件40年左右及其背景下13年左右的周期振荡.(2)类ENSO事件对亚洲-北太平洋-北美上空中高纬和副热带大气系统年代际变化具有重要影响.类El Ni(n)o成熟期间冬季,中高纬地区大气环流经向型发展,贝加尔湖高压脊加强,西太平洋副高偏强、位置偏西,蒙古高原为较强的异常反气旋环流.类El Ni(n)o衰退期(类La Ni(n)a发展期)夏季,贝加尔湖低压槽加深,乌拉尔山高压脊加强,西太平洋副高偏弱,新疆-河套地区为较强的异常反气旋环流距平.类La Ni(n)a事件时相反.(3)热带太平洋类ENSO事件通过影响中高纬和副热带大气系统,造成中国北部地区上空南风距平的年代际变化,进而导致东亚季风和中国气候异常.类El Ni(n)o事件成熟期,中国北部地区上空多异常偏北风,东亚季风弱,华北少雨,长江中、下游多雨;类El Ni(n)o衰退(类La Ni(n)a发展)期,中国北部地区上空亦为异常偏北气流,东亚季风较弱,华北少雨.中国气候异常型主要取决于类ENSO第一模态,而第二模态主要视位相异同来加强或减弱第一模态.两个类ENSO模态的共同作用导致1978年前后中国气候跃变和华北地区持续20余年的干旱.近期类ENSO模的振荡从1998年左右开始转为类La Ni(n)a模态,大致在2018年左右结束.在此期间,华北降水有望增加,长江中、下游降水可能减少.  相似文献   

11.
用1958～2000年NCEP/NCAR再分析资料、中国160站降水量及1958～1998年月平均海温资料分析了中国夏季相邻月份降水异常型的相关特征，及其与大气热源的关系和相关物理过程。结果表明，7月长江流域的降水异常与8月长江和黄河之间地区的降水异常有很好的同号性。7、8月长江流域及附近地区持续性偏旱（涝）与太平洋洋盆尺度的大气热源异常有关，并与前期5、6月热带中、东太平洋大范围的热源异常、青藏高原热源异常也有密切的联系，即当5、 6月赤道东太平洋的大气热源正异常，而赤道中太平洋北侧的热源负异常，则中国7月长江中下游偏涝，8月长江中上游与江淮流域和内蒙古东部偏涝，华南偏旱；反之亦然。前期热带中、东太平洋上空的热源异常中心和与之联系的异常垂直运动中心的西扩和西移，以及青藏高原东部的热源异常中心是影响我国7、8月持续偏旱（涝）的重要环流异常特征。另外，南海－西太平洋海温在前期也已经具有我国夏季长江流域发生旱涝对应的同期海温异常分布型的特征。  相似文献   

12.
Influence of North Atlantic sea surface temperature (SST) anomalies on tropical Pacific SST anomalies is examined. Both summer and winter North Atlantic SST anomalies are negatively related to central-eastern tropical Pacific SST anomalies in the subsequent months varying from 5 to 13?months. In particular, when the North Atlantic is colder than normal in the summer, an El Ni?o event is likely to be initiated in the subsequent spring in the tropical Pacific. Associated with summer cold North Atlantic SST anomalies is an anomalous cyclonic circulation at low-level over the North Atlantic from subsequent October to April. Corresponded to this local response, an SST-induced heating over the North Atlantic produces a teleconnected pattern, similar to the East Atlantic/West Russia teleconnection. The pattern features two anticyclonic circulations near England and Lake Baikal, and two cyclonic circulations over the North Atlantic and near the Caspian Sea. The anticyclonic circulation near Lake Baikal enhances the continent northerlies, and strengthens the East-Asian winter monsoon. These are also associated with an off-equatorial cyclonic circulation in the western Pacific during the subsequent winter and spring, which produces equatorial westerly wind anomalies in the western Pacific. The equatorial westerly wind anomalies in the winter and spring can help initiate a Pacific El Ni?o event following a cold North Atlantic in the summer.  相似文献   

13.
中国东部夏季分区降水对海温异常响应特征的研究   总被引：6，自引：5，他引：1  
用刘征宇最新发展的广义平衡反馈方法结合经验正交分析和旋转经验正交分析法,研究中国东部6个分区夏季降水异常对各海盆海温异常(SSTA)模态的响应特征,探讨了东北区降水异常对SSTA的响应机制。结果表明:各分区降水异常对SSTA的响应特征有明显差异。东北区降水异常对热带太平洋SSTA的回应显著,当SSTA表现为类似El Niño模时,该区夏季降水增加;江淮区降水异常同时受到中纬度以及热带SSTA的强迫,对热带太平洋SSTA的类似La Niña Modoki模、北大西洋SSTA三极型模等回应显著;西南地区的降水异常主要与中纬度SSTA有密切关联。对流层高度场对热带太平洋SSTA类似El Niño模的直接回应在热带太平洋上空为显著正异常。通过东亚—太平洋型遥相关波列使东北地区上空高度场出现负异常,并在其西侧形成负异常中心,对流层低层为气旋性环流异常。这一环流回应与东北地区夏季降水偏多时的环流特征相近。  相似文献   

14.
龙振夏  李崇银 《大气科学》2001,25(2):145-159
利用LASG九层大气环流谱模式及IAP两层大气环流模式，模拟研究了不同持续时间的赤道东太平洋海表温度正异常(海表温度异常的持续时间分别为1月份，1～2月份，1～4月份及1～8月份，其他月份为气候SST)对西太平洋副高的影响。结果表明，尽管海表温度异常的持续时间不同，但其引起的西太平洋副高的异常演变及其分布却十分相似；同时，季风区的异常降水(进而异常潜热释放)随时间的演变及其分布也存在一定的相似性(对应于不同持续时间的赤道东太平洋的海表温度正异常，5月份印度洋至西太平洋地区都表现出赤道辐合带北移偏晚的特征)；季风区降水的这种变化同西太平副高的异常是一致的，从而揭示出这两种现象有可能存在着某种联系。结果还表明，导致这种大气响应场对赤道东太平洋海表温度异常持续时间不敏感的一个重要原因是大气内部过程的影响:中纬大气的内部Rossby波源维持了热带地区激发的扰动在中高纬的存在，同时大气内部Rossby波源对赤道太平洋地区的海表温度异常持续时间表现出不敏感性，正是由于这种不敏感性才导致了响应场对赤道太平洋地区海表温度异常持续时间的不敏感性。模拟结果还表明，在夏季赤道东太平洋存在海表温度正异常的情况，尽管大气内部动力过程的作用十分重要，但夏季赤道东太平洋海表温度正异常对夏季西太平洋副高的影响却明显存在，因此，基于赤道太平洋地区海表温度异常的夏季西太平洋副高的可预报性受到赤道东太平洋海表温度正异常及大气内部动力过程的双重影响。模式的依赖性研究表明，模拟结果具有一定的普遍性。  相似文献   

15.
张书萍  祝从文  周秀骥 《大气科学》2014,38(5):1005-1016
本文利用1951～2011 年期间中国台站资料、东亚地区的探空资料、NCEP/NCAR 和ERA40 等大气再分析资料,通过对水分平衡方程诊断探讨了华北地区过去60 年中水资源和可利用降水量的变化特征及其与大尺度环流变化之间的关系。结果发现,华北地区69%的降水量被蒸发,可利用降水仅仅为降水量的31%。夏季可利用降水是华北水资源的主要来源,华北夏季可利用降水量在80 年代初发生突变减少,进入21 世纪初,伴随蒸发量的增加该地区可利用降水量进一步减少。西风带水汽与东亚夏季风水汽是华北可利用降水的主要来源。NCAR/NCEP 和EAR40 再分析资料的结果均显示贝加尔湖一带的位势高度偏低和西太平洋高压的偏强有利于该地区降水增多。利用探空资料进一步证明,蒙古以及贝加尔湖地区的温度在对流层低层变暖和位势高度场的加强导致了过去几十年华北可利用降水量减少。由于贝加尔湖地区温度变化与全球变暖存在密切关联,监测该地区温度的变化对预测华北水资源和东亚夏季风的长期变化具有重要的意义。  相似文献   

16.
利用1999—2008年5—8月中国160站月平均气温资料、每日2次的MICAPS资料及每日4次的NCEP 1°×1°资料,通过定义一个夏季华北冷涡强度指数(NCCVI),研究了夏季华北冷涡异常年西太平洋副高、东亚季风、高空急流及低层垂直运动的异常特征。结果表明：夏季NCCVI异常强年500 hPa上贝加尔湖地区有气旋性环流发展,从贝加尔湖至我国华北地区为一显著的高空槽所控制,冷空气较活跃并随槽后引导气流扩散南下影响华北地区。对流层各层偏暖湿,200 hPa上高空急流偏强,700 hPa上高纬冷涡后部偏北气流加强,低纬偏南气流加强,冷暖空气在华北交汇,华北和东北地区低层上升运动发展。同期副热带高压偏强,位置略偏南;东亚夏季风偏强, 加强了水汽输送。夏季NCCVI异常弱年相反。  相似文献   

17.
The temporal clustering of the western North Pacific tropical cyclogenesis and its modulation by the Madden–Julian oscillation (MJO) during the 1991 summer were examined based on the tropical cyclone best track, outgoing longwave radiation, and NCEP/NCAR reanalysis datasets. The wavelet analysis shows that convective activities around the monsoon trough in the western North Pacific possessed a distinct MJO with a period of 20–60 days. Two or more tropical cyclones were observed to form successively during each active phase of the MJO, and tropical cyclones tended to generate around the southeastern part of the maximum vorticity of the low-frequency cyclonic circulation during the developing and peak stages of the active MJO phase. But tropical cyclogenesis scarcely occurred during inactive MJO phases. Thus the MJO was a major agent in modulating repeated development of tropical cyclones in the western North Pacific during the 1991 summer. The MJO in circulation was characterized by a huge anomalous cyclone (anticyclone) in the lower troposphere existing alternately over the western North Pacific, leading to an enhanced (weakened) monsoon trough. An examination of the meridional gradient of absolute vorticity associated with the zonal flow indicates that the zonal flow in the monsoon trough region satisfied the necessary conditions for barotropic instability, with both zonal flow and the meridional gradient of absolute vorticity varying on the similar MJO timescale. The intraseasonal oscillation of such an unstable zonal flow might thus be an important mechanism for temporal clustering of tropical cyclogenesis in the western North Pacific. The barotropic conversion could provide a major energy source for the formation and growth of tropical cyclones in the western North Pacific during active MJO phases, with the eddy kinetic energy generation being dominated by both terms of eddies interacting with zonal and meridional gradients of the basic zonal flow.  相似文献   

18.
基于美国环境预报中心/国家大气研究中心（NCEP/NCAR-Ⅰ）再分析资料,按照国际通行的阻塞高压（阻高）定义,采用计算机自动识别和天气图人工主、客观相结合的检测方法,获得了1979—2018年5月和6月逐日北半球中高纬度阻高活动的无缝隙分布;并利用线性相关和信息流因果关系等统计方法,研究了东北亚（鄂霍次克海）阻高与北半球其他阻高活动区特征及其联系。根据阻高活动集中程度与占北半球活动总天数的百分比,选定8个5月阻高主要活动区和10个6月阻高主要活动区。从统计结果来看,5月北太平洋、北美和乌拉尔山阻高活动占前3位,6月东北亚阻高活动天数跃升第1位。值得注意的是,初夏在贝加尔湖以南、青藏高原以北地区出现了明显的阻塞形势,称为青藏高原北阻高。5月和6月北半球各阻高活动中心集中的纬度分布,自西向东具有“正弦波”特征,其主要活动区引起的同期北半球500 hPa高度场的异常虽不尽相同,但均具有一定的遥相关特征;5月和6月东北亚阻高活动天数的年际变化分量具有明显的相对独立性。5月东北亚阻高是6月贝加尔湖阻高活动年际变化的稳定影响源,是6月青藏高原北阻高活动年际变化的不稳定影响源;唯有5月北太平洋阻高是6月东北亚阻高年际变化的稳定影响源。2019年6月北半球阻高活动异常的区域位于欧洲,达19 d,为气候平均值（7 d）的2.7倍,也是导致欧洲大陆初夏高温的主要影响系统。   相似文献   

19.
We identified the Asian–Pacific Oscillation (APO) and its associated index, a zonal teleconnection pattern over the extratropical Asian–Pacific region. This was done through the correlation and empirical orthogonal function (EOF) analyses on the summer mean tropospheric eddy temperature from the monthly European Center for Medium-Range Weather Forecast reanalysis. The APO reflects an out-of-phase relationship in variability of the eddy temperature between Asia and the North Pacific and is associated with the out-of-phase relationship in atmospheric heating. The APO index shows a decadal variation, tending to a high-index polarity before 1975 and afterward to a low-index polarity. Moreover, the APO index has a quasi-5-year period. With higher APO-index conditions in the upper troposphere, the summer South Asian high and the North Pacific trough are stronger, while the westerly jet stream over Asia and the easterly jet stream over South Asia strengthen. Also, the Asian low and the North Pacific subtropical high are stronger in the lower troposphere. The anomalous southerlies prevail at the midlatitudes of East Asia, accompanied by a more northward Mei-yu front, and the anomalous westerlies prevail over South Asia. Summer rainfall increases in North China, South China, and South Asia, while it decreases from the valley of the Yangtze River to southern Japan, and near the Philippines.  相似文献   

20.
2005年夏季的主要天气及其环流分析   总被引：10，自引：2，他引：8  
简要讨论了2005年夏季的主要天气过程和形势。2005年夏季全国大部分地区降雨量接近常年同期或偏多,特别是新疆地区降雨异常偏多,华南地区出现严重洪涝,而长江流域出现了空梅。造成6月华南地区强降雨的影响天气系统为切变线和地面静止锋,主要为从东北和西北来的冷空气与暖湿气流交汇于华南地区而形成。2005年与1994、1998年环流的对比表明,1998年西南季风强度比1994、2005年都要弱,但2005年梅雨期东阻位置在贝加尔湖东侧,比1998年的鄂霍次克阻高偏西,中纬度地区多小槽活动,贝加尔湖地区没有长波槽建立,中高层西风急流带偏北大约10个纬度,低层西南风急流也偏北,有利于北方降水的发生。2005年夏季登陆我国的台风偏多,强度较强,这是又一特点。华北地区的暴雨过程多与登陆或西太平洋上活动的台风有关;东北地区多低涡活动。与2004年对比,2005年华北地区的高温日数偏多,而且出现持续闷热天气,江南部分地区的高温天数也偏多。  相似文献   

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