Phase transition of the Pacific decadal oscillation and decadal variation of the East Asian summer monsoon in the 20th century   总被引：1，自引：0，他引：1  

Xiao Dong  Feng Xue 《大气科学进展》2016,33(3):330-338

This paper focuses on the relationship between the phase transition of the Pacific decadal oscillation (PDO) and decadal variation of the East Asian summer monsoon (EASM) in the twentieth century. The first transition occurred in the 1940s, with an enhanced SST in the North Pacific and reduced SST in the tropical eastern Pacific and South Indian Ocean. In agreement with these SST changes, a higher SLP was found in most parts of the Pacific, while a lower SLP was found in the North Pacific and most parts of the Indian Ocean. In this case, the EASM was largely enhanced with a southerly anomaly in the lower troposphere along the east coast of China. Correspondingly, there was less rainfall in the Yangtze River valley and more rainfall in northern and southern China. An opposite change was found when the PDO reversed its phase in the late 1970s. In the tropical Indian Ocean and western Pacific, however, the SST was enhanced in both the 1940s and 1970s. As a result, the western Pacific subtropical high (WPSH) tended to extend westward with a larger magnitude in the 1970s. The major features were reasonably reproduced by an atmospheric general circulation model (IAP AGCM4.0) prescribed with observed SST and sea ice. On the other hand, the westward extension of the WPSH was exaggerated in the 1970s, while it was underestimated in the 1940s. Besides, the spatial pattern of the simulated summer rainfall in eastern China tended to shift southward compared with the observation.  相似文献   

Occurrence,durée et intensité des précipitations simulées par deux modèles régionaux canadiens du climat sur la région du Maghreb     

Mariem Jelassi  Philippe Gachon  René Laprise 《大气与海洋》2016,54(5):469-497

[Translated by the editorial staff] Simulating the precipitation regime of Northern Africa is challenging for regional climate models, particularly because of the strong spatial and temporal variability of rain events in the region. In this study we evaluate simulations conducted with two recent versions of regional climate models (RCM) developed in Canada: the CRCM5 and CanRCM4. Both are also used in the COordinated Regional Climate Downscaling EXperiment (CORDEX)-Africa. The assessment is based on the occurrence, duration, and intensity indices of daily precipitation in Maghreb during the fall and spring seasons from 1998 to 2008. We also examine the links between the North-Atlantic Oscillation (NAO) index, weather systems, and the precipitation regime over the region. During the rainy season (September to February), the CRCM5 reproduces the frequency and intensity of extreme precipitation adequately, as well as the occurrence of days with rain, while the CanRCM4 underestimates precipitation extremes. The study of links between weather systems and the precipitation regime shows that, along the Atlantic coast, precipitation (occurrence, intensity, and wet sequences) increases significantly with storm frequency in the fall. In winter, these links grow stronger going east, from the Atlantic coast to the Mediterranean coast. The negative phases of the NAO index are statistically associated with the increase in rain intensity, extremes, and accumulation along the Atlantic coast in the fall. However, the link weakens in winter over these regions and strengthens along the Mediterranean coast as the precipitation frequency rises during negative phases of the NAO. Both RCMs generally reproduce the links between the NAO and the precipitation regime well, regardless of location.  相似文献   

2007年夏季江淮强降水过程中10~30d低频变化及其与对流层上层波包活动的联系          下载免费PDF全文

陈丹萍  管兆勇  侯俊  奚子惠 《大气科学学报》2016,39(2):177-188

利用NCEP/NCAR再分析和全国740站逐日降水资料,运用一点滞后相关等方法,对2007年夏季江淮流域强降水期间低频振荡的波动活动特征及其与降水低频变化的联系进行了分析。结果表明,在2007年夏季降水中,降水低频分量起着重要作用。降水的低频振荡主周期为10~30d,降水距平时间序列与10~30d低频分量具有较好的对应关系。低频扰动在对流层上层和低层都呈现波列状分布,且在降水活跃位相时,低频环流在高、低层具有斜压结构。在对流层上层,低频扰动有缓慢的东移倾向,相速度为每天2~3个经度。西风带中存在多次移动性波列向下游的传播,且在120°E以西以每天14经度的群速度向下游频散能量,表明10~30d低频波动具有明显的下游发展特征。在强降水开始5d前,低频波动与能量可起源于高纬的乌拉尔山附近,沿着西北-东南向的路径向下游传播。下游发展的低频波动为江淮流域带来了能量,为强降水的发生提供了条件。这些结果加深了人们对低频波动在江淮流域强降水过程中所起作用的认识,可为寻找江淮流域强降水过程预报线索提供科学依据。  相似文献   

1980-2010年冬季北极涛动季节内振荡的成因分析          下载免费PDF全文

沈新勇  王涛  赵南  黄伟  王乙舒  崔妍 《大气科学学报》2016,39(1):1-7

采用NCEP/NCAR日平均再分析资料,对冬季热带外低频振荡(大气角动量收支及地形力矩)与AO(Arctic Oscillation)指数进行计算,通过功率谱和统计分析发现,它们都存在30~60 d的周期,大气角动量收支与山脉力矩的变化为正相关,且显著响应AO变化。通过动力学诊断分析初步认为,北半球两大地形的山脉力矩作用于纬向大气角动量,副热带纬向西风发生变化,改变南北西风偶极子结构,使得AO产生变化,而且在两大地形中以喜马拉雅山脉地形作用为主。通过对喜马拉雅山脉地区的动力学诊断发现,在高(低)AO指数阶段,喜马拉雅山脉地区激发准定常行星波并作用于副热带西风,导致副热带西风偏弱(偏强),高纬西风偏强(偏弱),因而AO偏强(偏弱),平流层极涡偏强(偏弱),极涡强(弱)中心偏向东北亚。  相似文献   

致密星的X射线辐射时延现象     

屈进禄  宋黎明  吴枚  李年福 《天文学进展》2002,20(2):144-157

能谱仅反映了高能天体辐射的部分性质，而高能X射线辐射的时变可以反映致密天体的动态性质。因此，在构造高能辐射的理论模型时，既要考虑X辐射的能谱性质，也要考虑其时变性质。特别对高能天体X辐射的快速光变，一般认为其发生在致密天体附近，致密天体快速光变的研究可以揭示出致密天体附近的物理性质，因此，时变可以对X辐射模型给以很强的限制。X射线源不同能量光子到达观测者的时间差称为X射线辐射的时延。介绍了高能X辐射时变中的时延分析方法及其最新发展，综述了致密双星系统中黑洞侯选林和中子星的时延现象，并简单介绍了为解释这些现象所发展的模型，以及时延对模型的限制。  相似文献   

非线性Rossby波所满足的三阶Zakharov方程与低频振荡     

罗德海 《成都信息工程学院学报》1993,(4)

本文在基本气流具有水平切变的情况下,利用摄动法导出了非线性Rossby波所满足的三阶Zakharov方程,然后,考虑了基流具有弱切变的情况,通过使用三阶Zakharov方程研究了Rossby波列的第一类不稳定性问题。结果表明:通过非线性作用,大气中的Rossby波列可产生调制不稳定。同时,本文对这种不稳定的区域,增长率和周期进行了详细的计算,并讨论了波振幅、波数、纬度和基流切变对它们的影响,指出Rossby波列的调制不稳定可以激发30～60天的低频振荡。  相似文献   

南极长城站地区气象要素的中期振荡特征   总被引：2，自引：0，他引：2       下载免费PDF全文

陆龙骅  卞林根  张永萍 《极地研究》1989,1(4):12-20

本文用多维谱分析的方法研究了1985年1月-1987年12月南极长城站地面气象要素的谱特征。该地区的气象要素与北半球一样,也普遍存在3-5天、准一周、准二周和3-4周振荡周期。在长城站所在的乔治王岛地区,从地面到平流层中下部,气压系统都存在着显著的准二周振荡,这种振荡是由上往下传播的。无论冬、夏季,准二周和准一周振荡都是由西往东传播的,而扰动的南北传播方向则与季节及振荡周期长度有关。南极地区的中期振荡特征与500hPa极地涡旋的活动和强度变化有密切关系。  相似文献   

Seasonal oscillations in mesospheric temperatures at low-latitudes     

Y. Zhao  M.J. Taylor  H.-L. Liu  R.G. Roble 《Journal of Atmospheric and Solar》2007,69(17-18):2367

Using 3 years of high-quality temperature measurements (2002–2004) recorded from Maui, HI (20.8°N), we have investigated the characteristics of mesospheric seasonal oscillations at low-latitudes. Measurements of the near-infrared OH (6,2) and O₂ (0,1) nightglow emission layers (centered at 87 and 94 km) independently reveal a distinct semi-annual oscillation (SAO) and annual oscillation (AO) with amplitudes of 3.8 and 2.0 K, respectively. An observed asymmetry in the seasonal variation of the nocturnal mean, previously reported by Taylor et al. [2005. Characterization of the semi-annual-oscillation in mesospheric temperatures at low-latitudes. Advances in Space Research 35, doi:10.1016/j.asr.2005.05.111] from this site is shown to be due to a superposed AO of amplitude 50% of the SAO signature. Detailed investigations of the local-time variation of the SAO amplitude and phase combined with TIME-GCM simulations of the seasonal variation of the diurnal tide strongly suggest a large local-time dependence of the amplitude (but not phase) of the observed SAO. These data indicate that the true mean temperature SAO amplitude could be as high as 7 K at this latitude.  相似文献   

地震和潮汐对气候波动变化的影响          下载免费PDF全文

杨冬红  杨德彬  杨学祥 《地球物理学报》2011,54(4):926-934

2004年12月26日印尼地震海啸后,全球低温冻害和暴雪灾害频繁发生."潮汐调温说"和"深海巨震降温说"是一种合理的解释.根据"潮汐调温说"和"深海巨震降温说"理论,2005年以后全球气温将因为地震海啸和强潮汐南北震荡而降低.2009年11月至2010年1月低温暴雪袭击北半球,西方科学家也承认2000～2010年气候的...  相似文献   

厄尔尼诺事件和拉尼娜事件的成因与预测   总被引：5，自引：0，他引：5  

杨冬红  杨学祥 《沙漠与绿洲气象(新疆气象)》2008,2(5):1-10

通过对南极气温资料、环南极海冰资料、臭氧变化资料、太平洋海温资料、地球自转速度变化资料、厄尔尼诺和拉尼娜资料的综合验证,发现了构造运动与厄尔尼诺因果关系。大气、海洋与岩石圈的角动量交换在南半球和北半球有不同的形式,这是由陆海分布的差异决定的。南极上空臭氧变化和环南极海冰变化是赤道海温和全球气候准两年振荡的原因。其中,德雷克海峡的海冰变化起主要作用。这个结论给出了作者提出的“海洋锅炉效应”、“臭氧洞漏能效应”、“德雷克海冰气候开关效应”和“大洋地壳跷跷板运动”的相互关系,证明构造运动对厄尔尼诺的重要影响。强潮汐准4a周期的发现,表明南极海冰变化、东太平洋海温变化、地球自转变化和厄尔尼诺都具有4a准周期变化的原因。海温和海冰开关的准2a周期和日食-厄尔尼诺系数理论有较好的预测效果。  相似文献