首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到19条相似文献，搜索用时 140 毫秒
1.
The connection of the Arctic Oscillation(AO)with the frequency of temperature extremes over East Asia during boreal winter has been documented by many studies.This study describes an asymmetry in the relationship between the January AO and the simultaneous cold extremes in Northeast China(NEC),and further reveals a breakdown of this relationship.It is demonstrated that the frequency of January cold extremes in NEC shows significant(insignificant)negative correlation with the simultaneous negative(positive)phase of the AO.One possible explanation for such an asymmetry is that the Arctic center of negative AO extends more southwards to Siberia compared with that of positive AO,conducive to a closer connection with the frequency of an extreme Siberian high.As a result,the frequency of January cold extremes in NEC shows a more significant relationship with the negative AO.The other related explanation is that,concurrent with the negative phase of the AO,there is an evident meridional stationary planetary wave in the upper troposphere around(30°N,100–300 hP a),which disappears in the positive AO.Therefore,the negative AO could better reflect the fluctuation of the subtropical westerly wind and the synoptic-scale transient wave activity,which is closely related to the frequency of cold extremes in NEC.Along with a positive polarity of the AO trend since the mid-1980s,the connection between the cold extremes over NEC and the AO during January has been weakened.  相似文献   

2.
This paper demonstrates regional characteristics, a long-term decreasing trend, and decadal variations in the frequency of cold surge events based on daily mean temperature and daily minimum temperature data in mainland China from 1960 to 2008. During these 48 years, four high frequency centers of cold surge events were located in Xinjiang, central North China, northeast China, and southeast China. A main frequency peak of cold surge events occurs in autumn for the four regions and another peak is detected in spring over northeast China and southeast China. The regional pattern of cold surge frequencies is in accordance with the perturbation kinetic energy distribution in October-December, January, and February-April. The long-term decreasing trend （-0.2 times/decade） of cold surge frequencies in northeast China and decadal variations in China are related to the variations of the temperature difference between southern and northern China in the winter monsoon season; these variations are due to the significant rising of winter temperatures in high latitudes.  相似文献   

3.
By using the observed monthly mean data over 160 stations of China and NCAR/NCEP reanalysis data, the generalized equilibrium feedback assessment(GEFA) method, combined with the methods of EOF analysis, correlation and composite analysis, is used to explore the influence of different SST modes on a wintertime air temperature pattern in which it is cold in the northeast and warm in the southwest in China. The results show that the 2009/2010 winter air temperature oscillation mode between the northern and southern part of China is closely related to the corresponding sea surface temperature anomalies(SSTA) and its associated atmospheric circulation anomalies. Exhibiting warming in Northeast China and cooling in Southwest China, the mode is significantly forced by the El Nio mode and the North Atlantic SSTA mode, which have three poles. Under the influence of SSTA modes, the surface northerly flow transported cold air to North and Northeast China, resulting in low temperatures in the regions. Meanwhile, the mid-latitude westerlies intensify and the polar cold air stays in high latitudes and cannot affect the Southwest China, resulting in the warming there.  相似文献   

4.
The surface and upper-level features associated with a sharp drop of wintertime daily temperature over South Korea is investigated in this study. This sharp drop in daily temperature is called a cold surge and is one of the most hazardous weather phenomena in East Asian winters. An upper-level baroclinic wave of 60°wavelength propagating eastward at a phase speed of 12°longitude per day across the continent of northern China from the west of Lake Baikal toward the eastern coast of China causes the outbreak of cold air over South Korea. The cooling associated with the upper-level baroclinic wave is found at all altitudes under the geopotential height-fall center near the tropopause. The development in the ridge seems to derive the early evolution of the eastward-propagating sinusoidal wave, whereas the trough is connected directly with the tropospheric temperature-drop. An enhancement of the wintertime East Asian jet stream after the outbreak of a cold surge is a response to the steep temperature gradient associated with the developing baroclinic wave.  相似文献   

5.
Using NCEP/NCAR reanalysis data, the China rainfall and surface temperature data of the China Meteorological Administration, and the Arctic Oscillation (AO) indices of NOAA, the author investigates relationships between the AO and the precipitation and temperature over China. There exists a good relationship between the AO index in December and the succeeding January precipitation over South China, indicating that when the December AO index is positive (negative), the January precipitation over South China increases (decreases). A remarkable negative correlation between the December AO index and the January surface temperature also exists over South China, indicating that when the December AO index is positive (negative), the January temperature over South China drops (rises). The occurrence of this anomalous climate is related to the anomalies of the atmospheric circulation systems. The December AO greatly influences circulation anomalies in January. A positive phase of the AO is found to lead to a stronger subtropical jet over the south side from the Iran Plateau to the Tibetan Plateau. Consequently, it results in a deepening pressure trough around the Bay of Bengal, which transports the warm and wet air to South China continuously. The Siberian High in January is stronger and extends farther southeastward. It results in continual cold air at 1000 hPa pouring into South China, inducing low temperature. Cooperating with the trough of the Bay of Bengal, anomalous precipitation occurs over South China. For the negative phase of the December AO, the opposite situation is observed.  相似文献   

6.
The region of south China is sometimes subject to major climatic catastrophes in winter. To have a clear understanding, the time in which extremely severe cold months occur in the south China wintertime over the past 45 years are determined and characteristics of the 500-hPa geopotential fields and SST fields are studied for the simultaneous and preceding 6-month periods. Similarity exists in the 500-hPa geopotential fields between each current severely cold month, with the geopotential pattern of being high in the north, but low in the south, of Asian-Pacific region and meridional circulation developing. The work presents anomalies of the months with significant differences in the 500-hPa geopotential field of the previous periods. The SSTA is continuous in the distribution from each extremely severe cold winter month back to the 6 months leading up to it for the region of south China while the SST pattern is of El Ni?o in January and the preceding 1 ~ 6 months for equatorial eastern Pacific but of La Ni?a in February and December. It is concluded that the prediction of severely cold winter months are possible with the use of the geopotential field at 500 hPa and the SST fields for the months ahead of the target time.  相似文献   

7.
In the present study, the authors investigated the relationship between the Arctic Oscillation (AO) and the high-frequency variability of daily sea level pressures in the Northern Hemisphere in winter (November through March), using NCEP/NCAR reanalysis datasets for the time period of 1948/49-2000/01.High-frequency signals are defined as those with timescales shorter than three weeks and measured in terms of variance, for each winter for each grid. The correlations between monthly mean AO index and high-frequency variance are conducted. A predominant feature is that several regional centers with high correlation show up in the middle to high latitudes. Significant areas include mid- to high-latitude Asia centered at Siberia, northern Europe and the middle-latitude North Atlantic east of northern Africa. Theirs trong correlations can also be confirmed by the singular value decomposition analysis of covariance between mean SLP and high-frequency variance. This indicates that the relationship of AO with daily Sea Level Pressure (SLP) is confined to some specific regions in association with the inherent atmospheric dynamics. In middle-latitude Asia, there is a significant (at the 95% level) trend of variance of-2.26% (10yr)^-1. Another region that displays a strong trend is the northwestern Pacific with a significant rate of change of 0.80% (10 yr)^-1. If the winter of 1948/49, an apparent outlier, is excluded, a steady linear trend of 1.51% (10 yr)^-1 shows up in northern Europe. The variance probability density functions (PDFs) are found to change in association with different AO phases. The changes corresponding to high and low AO phases, however, are asymmetric in these regions. Some regions such as northern Europe display much stronger changes in high AO years, whereas some other regions such as Siberia show a stronger connection to low AO conditions. These features are supported by ECMWF reanalysis data. However, the dynamical mechanisms involved in the AO-high frequency SLP variance connection have not been well understood,and this needs further study.  相似文献   

8.
The severe rainfall events in the mid-summer of July 2004 and the roles of cold air in the forma- tion of heavy precipitation are investigated by using daily observational precipitation data of China and NCEP/NCAR reanalysis.The results show that the severe rainfalls in Southwest China are closely related to the cold air activities from the mid-high latitudes,and the events take place under the cooperative effects of mid-high latitude circulation and low latitude synoptic regimes.It is the merging of a cold vortex over mid-latitudes with the northward landing typhoon and eastward Southwest China Vortex,as well as the abrupt transformation from a transversal trough into an upright one that causes three large alterations of mid-high atmospheric circulation respectively in the early and middle ten days of this month.Then,the amplitude of long waves soon magnifies,leading to the unusual intrusion of cold air to low-latitude areas in the mid-summer.Meanwhile,the warm and humid southwest summer monsoon is quite active.The strong interactions of cold air and summer monsoon over Southwest China result in the large-scale convective rain- falls on the southern side of cold air. With regard to the activities of cold air,it can influence rainfalls in three prominent ways.Firstly,the incursion of upper-level cold air is often accompanied by partial southerly upper-level jet.The ascending branch of the corresponding secondary circulation,which is on the left front side of the jet center,provides the favorite dynamic upward motion for the rainfalls.Secondly,the southward movement of cold air contributes to the establishment of atmospheric baroclinic structure,which would lead to baroclinic disturbances.The atmospheric disturbances associated with the intrusion of cold air can destroy the potential instability strat- ification,release the convective available potential energy(CAPE)and finally cause convective activities.In addition,the advection processes of dry and cold air at the upper level along with the advection of humid and warm air at the lower level are rather significant for the reestablishment of potential instability in the precipitation area,which is one of the crucial factors contributing to persistent rainfalls.  相似文献   

9.
Partial Least Squares Regression （PLSR） is used to study monthly changes in the influence of the Arctic Oscillation （AO） on spring, summer and autumn air temperature over China with the January 500 hPa geopotential height data from 1951 to 2004 and monthly temperature data from January to November at 160 stations in China. Several AO indices have been defined with the 500-hPa geopotential data and the index defined as the first principal component of the normalized geopotential data is best to be used to study the influence of the AO on SAT （surface air temperature） in China. There are three modes through which the AO in winter influences SAT in China. The influence of the AO on SAT in China changes monthly and is stronger in spring and summer than in autumn. The main influenced regions are Northeast China and the Changjiang River drainage area.  相似文献   

10.
Systematic studies on the cryosphere in China started in the late 1950s. Significant achievements have been made by continuous investigation of glacier inventories, frozen ground observations, paleo-climate analyses of ice cores, process studies and the modeling of cryopsheric/atmospheric interactions. The general facts and understanding of these changes include： （1） Solid precipitation, including the number of days with frost and hail storms, shows a decreasing tendency over the past half century. （2） In most areas glaciers are retreating or have completely vanished （〉80%）, some glaciers are still advancing （5%-20% depending upon time period）. The annual glacial melt water has been increasing since the 1980s. This increased supply of melt water to river runoff in Northwest China is about a 10%-13%. （3） The long-term variability of snow cover in western China is characterized by a large inter-annual variation superimposed on a small increasing trend. Snow cover variability in the Qinghai-Xizang Plateau （QXP） is influenced by the Indian monsoon, and conversely impacts monsoon onset and strength and eventually the drought and flood events in middle-low reaches of Yangtze River. （4） Frozen ground, including permafrost, is decaying both in QXP and in Northeast China. The most significant changes occurred in the regions with thickest seasonal frozen ground （SFG）, i.e., inland QXP, then northeastern and northwestern QXP. The cold season air temperature is the main factor controlling SFG change. The increase of ground surface temperatures is more significant than air temperature. （5） The sea ice coverage over the Bohai Sea and Yellow Sea has deceased since the 1980s. （6） River ice duration and ice thickness is also decreasing in northern China.
In 2001, the Chinese National Committee of World Climate Research Program/Climate and Cyosphere （WCRP/CliC） （CNC-CliC） was organized to strengthen research on climate and cryosphere in China. Future monitoring of the cryosphe  相似文献   

11.
中国冬季积雪变异及其与北极涛动的联系   总被引：1，自引：0，他引：1  
本文利用1979～2010年NCEP/NCAR再分析资料、中国台站观测雪深、气温和降雪资料, 分析了中国冬季积雪时空分布特征, 结果表明:雪深经验正交分解第一模态有显著的南、北反位相特征, 当新疆北部、东北地区积雪偏多(少)时, 对应黄河以南和青藏高原地区积雪偏少(多)。近30年来中国冬季积雪变异与北极涛动(AO)有非常紧密的联系, 雪深的南、北反位相分布型与北极涛动有明显的反相关关系。AO负位相时, 500 hPa等压面上40°N以北存在着中心在贝加尔湖附近的气旋环流, 而在其南存在着中心在中国西南的反气旋性环流, 中国北方和南方地区分别受气旋和反气旋的控制。在我国北方地区, 与AO相联系的气旋环流异常导致降雪增多、地表温度偏低, 使得积雪增加;而在南方地区, 与AO相联系的反气旋性环流异常导致的降雪减少和气温偏高, 导致了积雪减少。本文的研究说明了北极涛动通过影响中国降雪和气温, 进而对中国冬季积雪产生可能的影响。  相似文献   

12.
利用NCEP/NCAR再分析资料、北极涛动（AO）指数序列及中国160个台站月温度资料,分析1951-2007年中国冬季气温与AO指数的变化特征及其相互关系。结果表明：1951-2007年AO与中国东部地区冬季气温基本呈正相关关系。中国东部地区冬季气温指数（IWT）与北极涛动指数（IAO）均逐渐增强,并有显著的年际和年代际变化,均存在准18 a的周期变化特征。从偏相关系数来看,在年际尺度上,西伯利亚高压对中国东部地区冬季气温的年际变化影响较大,而AO与冬季气温无显著相关关系;在年代际尺度上,AO对中国东部地区冬季气温的影响较显著,比西伯利亚高压影响大。东亚大槽偏弱时,中国冬季气温偏高,AO指数也偏高,反之则相反。在年际尺度上,东亚大槽对中国东部地区冬季气温的年际变化影响较大,而AO与冬季气温无显著相关关系;在年代际尺度上,AO和东亚大槽对中国冬季气温的变化影响均较显著。  相似文献   

13.
冬季北极涛动与极涡的变化分析   总被引：11，自引：5，他引：11  
利用NCEP／NCAR资料计算出冬季极涡面积（PVA）指数和极涡强度（PVI）指数，对冬季北极涛动（AO）和北半球500hPa极涡指数进行周期分析，讨论了冬季AO与极涡的年际、年代际变化。结果表明：冬季AO指数与PVA指数呈反相关关系，与PVI指数呈正相关关系，且AO指数呈上升趋势，PVA指数呈下降趋势。冬季AO指数、PVA指数以及PVI指数均具有多重周期。强（弱）AO指数年，极地500hPa高度场降低（升高），PVI指数偏大（偏小），PVA指数偏小（偏大）。500hPa高度场上亚洲大槽、北美大槽均减弱（加强）。AO可激发出类似EU遥相关型的异常，从而影响到东亚地区的气候。冬季AO指数在1982年发生突变，且突变后北太平洋地区的正中心位置更靠东，强度更大。此外，AO突变前后极涡变化不是很显著。  相似文献   

14.
冬季平流层北极涛动对江南气温的影响   总被引：3，自引：2，他引：1  
利用ERA—interim及NCEP—DOE两种再分析资料,分析了冬季北极涛动（Arctic Oscillation,AO）与我国江南地区地表气温相关的时空结构。结果表明：1）2月30hPa的Ao指数与江南地区地表气温的同期相关系数最高,这与AO指数和江南地区地表气温的标准差均在2月极大有关。2）30hPa的正AO事件加强时,贝加尔湖地区对流层易出现显著的正位势高度异常,有利于东亚地区出现向南、向下的异常风场,与之对应,西伯利亚高压向南扩展,有利于北方冷空气南侵至我国江南地区,造成局地气温负距平;反之亦然。  相似文献   

15.
利用MM5V3区域气候模式单向嵌套ECHAM5全球环流模式的结果,对中国地区实际温室气体浓度下当代气候(1981—2000年)及IPCC A1B情景下21世纪中期气候(2041—2060年)分别进行了水平分辨率为50 km的模拟试验。首先检验全球和区域模式对当代气候的模拟情况,结果表明:区域模式对中国地区地面温度和降水空间分布的模拟能力优于全球模式;与实际观测相比,区域模式模拟的地面温度在中国大部分地区偏低,模拟的降水量偏多,降水位置偏北。IPCCA1B情景下中国地区21世纪中期气候变化的模式结果显示:各季节地面温度在全国范围内都将比当代升高1.2～3.9℃,且升温幅度具有北方大于南方、冬季大于夏季的时空分布特征;降水变化具有一定的区域性和季节性,秋季和冬季降水在全国大部分地区都将增加10%～30%,春季和夏季降水则呈现"北方减少、南方增多"的趋势,变化幅度在-10%～10%之间。21世纪中期地面温度和降水变化还具有一定的年际特征:地面温度在中国地区各子区域均表现为上升趋势,升温速率在0.7～0.9℃/10a之间,温度变率也比当代有所增大;降水在西北地区略呈下降趋势,在其它子区域均为上升,降水变率的变化具有区域性特征。  相似文献   

16.
20世纪90年代末东亚冬季风年代际变化特征及其内动力成因   总被引：10，自引：4，他引：6  
为纪念陶诗言先生对东亚冬季风研究的杰出贡献,本文利用我国测站、NCEP/NCAR和ERA-40/ERA-Interim再分析资料分析了我国冬季气温和东亚冬季风在20世纪90年代末所发生的年代际跃变特征及其内动力成因。分析结果表明:从20世纪90年代末之后,我国冬季气温和东亚冬季风发生了明显的年代际跃变。从1999年之后,随着东亚冬季风从偏弱变偏强,我国冬季气温变化从全国一致变化型变成南北振荡型（即北冷南暖型）,并由于从1999年之后我国北方冬季气温从偏高变成偏低,故冬季低温雪暴冰冻灾害频繁发生,同时,我国冬季气温和东亚冬季风年际变化在此时期从以往3～4 a周期年际变化变成2～8 a周期;并且,结果还表明了东亚冬季风此次年代际变化是由于西伯利亚高压和阿留申低压的加强所致。本文还从北极涛动（AO）和北半球准定常行星波活动的动力理论进一步讨论了此次东亚冬季风年代际跃变的内动力成因及其机理,结果表明:从20世纪90年代末之后,北半球冬季准定常行星波在高纬地区沿极地波导传播到平流层加强,而沿低纬波导传播到副热带对流层上层减弱,这造成了行星波E-P通量在高纬度地区对流层和平流层辐合加强,而在副热带地区对流层中、上层辐散加强,因而导致了北半球高纬度地区从对流层到平流层纬向平均纬向流和欧亚上空极锋急流减弱,而副热带急流加强,这造成了AO减弱和东亚冬季风加强。  相似文献   

17.
Interdecadal variability of observed winter precipitation in Southeast China (1961–2010) is characterized by the first empirical orthogonal function of the three-monthly Standardized Precipitation Index (SPI) subjected to a 9-year running mean. For interdecadal time scales the dominating spatial modes represent monopole features involving the Arctic Oscillation (AO) and the sea surface temperature (SST) anomalies. Dynamic composite analysis (based on NCEP/NCAR reanalyzes) reveals the following results: (1) Interdecadal SPI-variations show a trend from a dryer state in the 1970s via an increase during the 1980s towards stabilization on wetter conditions commencing with the 1990s. (2) Increasing wetness in Southeast China is attributed to an abnormal anticyclone over south Japan, with northward transport of warm and humid air from the tropical Pacific to South China. (3) In mid-to-high latitudes the weakened southward flow of polar airmasses induces low-level warming over Eurasia due to stronger AO by warmer zonal temperature advection. This indicates that AO is attributed to the Southeast China precipitation increase influenced by circulation anomalies over the mid-to-high latitudes. (4) The abnormal moisture transport along the southwestern boundary of the abnormal anticyclone over south Japan is related to anomalous south-easterlies modulated by the SST anomalies over Western Pacific Ocean; a positive (negative) SST anomaly will strengthen (weaken) warm and humid air transport, leading to abundant (reduced) precipitation in Southeast China. That is both AO and SST anomalies determine the nonlinear trend observed in winter precipitation over Southeast China.  相似文献   

18.
利用1961—2019年黑龙江省冬季气温、NCEP再分析资料和环流指数资料,采用多变量经验正交函数分解、合成分析、相关分析等方法,分析黑龙江省冬季气温季节内变化及其环流异常特征,并进一步对比了主要环流因子在冬季气温季节内演变不同模态中的相对贡献。结果表明: 季节内变化是黑龙江省冬季气温变化的基本特征。黑龙江省冬季气温存在季节内一致变化、12月和翌年1—2月反位相变化、12月至翌年1月和2月反位相变化三个主要模态。当冬季气温处于第一模态分布一致偏暖（冷）时,环流呈现北极涛动（AO）正（负）位相的分布特征,东亚冬季风（EAWM）偏弱（强）。当冬季气温发生季节内冷暖转换时,季内极涡、高空急流、西伯利亚高压（SH）和EAWM强度、中高纬环流经向度等均有明显调整。第二模态1月和第三模态2月环流场分别呈现类似极地欧亚型（PEA）和东大西洋型（EA）遥相关的分布特征。AO、SH、EAWM、PEA和EA是冬季气温季节内演变的重要影响因子。  相似文献   

19.
Based on the surface 2?m monthly minimum temperature from the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis dataset, the spatial and temporal characteristics of winter minimum temperature during 1961–2010 have been analyzed in China. Results showed that the minimum temperature in China has a significant increasing rate of 0.25° per decade calculated by the Mann–Kendall statistical test, which is consistent with the global warming trend. Empirical orthogonal function (EOF) analysis reveals that there are three main patterns that can explain more than 57.6% of the total variance of the winter minimum temperature. The EOF1, EOF2, and EOF3 account for 34.8%, 13.5%, and 13.5% of the total inter-annual variance, respectively. The EOF1, EOF2, and EOF3 patterns are synchronous in northern China, central China, and on the Tibetan Plateau. There exist a decrease trend in the corresponding time coefficients of EOF1 and EOF2 and an increase trend in that of EOF3 since the 1960s. Both the corresponding time coefficients of EOF1 and EOF2 have significant positive correlations with the 500?hPa geopotential heights of the Arctic region and negative correlations in the regions lower than 40°N, while a significant positive correlation is found between the corresponding time coefficients of EOF3 and 500?hPa geopotential heights in the low latitudes. This suggests that rapid warming occurs in northern China and on the Tibetan Plateau, while the weakest trend locates in southeast China. Thus, warming in winter is more pronounced at higher altitudes and latitudes. These patterns are tightly connected with the atmospheric circulation.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号