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1.
An Indian monsoon intraseasonal oscillations (MISO) index for real time monitoring and forecast verification 总被引：1，自引：1，他引：0
The wet/dry spells of the Indian summer monsoon (ISM) rainfall are governed by northward propagating boreal summer monsoon intraseasonal oscillations (MISO). Unlike for the Madden Julian Oscillation (e.g. RMM indices, Wheeler and Hendon in Mon Weather Rev 132:1917–1932, 2004), a low dimensional real-time monitoring and forecast verification metric for the MISO is not currently available. Here, for the first time, we present a real time monitoring index developed for identifying the amplitude and phase of the MISO over the ISM domain. The index is constructed by applying extended empirical orthogonal function (EEOF) analysis on daily unfiltered rainfall anomalies averaged over the longitudinal domain 60.5°E–95.5°E. The gravest two modes of the EEOFs together explain about 23 % of the total variance, similar to the variance explained by MISO in observation. The pair of first two principal components (PCs) of the EEOFs is named as MISO1 and MISO2 indices which together represent the evolution of the MISOs in a low dimensional phase space. Power spectral analysis reveals that the MISO indices neatly isolate the MISO signal from the higher frequency noise. It is found that the current amplitude and phase of the MISO can be estimated by preserving a memory of at least 15 days. Composite pictures of the spatio-temporal evolution of the MISOs over the ISM domain are brought out using the MISO indices. It is further demonstrated that the MISO indices can be used in the quantification of skill of extended range forecasts of MISOs. Since the MISO index does not rely on any sort of time filtering, it has great potential for real time monitoring of the MISO and may be useful in developing some prediction scheme. 相似文献
2.
Summary This study shows that precipitation over the United States has two time scales of intraseasonal variation at about 37 days
and 24 days. The results are derived from the application of a combination of statistical methods including principal component
analysis (PCA), singular spectrum analysis (SSA), and multi-channel singular spectrum analysis (MSSA) to over 10 years of
gridded daily precipitation records. Both oscillations have largest amplitude during the cold season. The 37-day oscillation
has larger interannual variability. Intraseasonal oscillations are most significant in the Pacific Northwest. The 37-day oscillation
has opposite phases between the western and eastern United States, while the 24-day oscillation has the same phases. These
intraseasonal time scale precipitation variations may be associated with previously revealed mid-tropospheric circulation
anomalies that oscillate at similar time scales.
Received February 7, 2000 Revised October 20, 2000 相似文献
3.
近百年东亚冬季风的突变性和周期性 总被引：42，自引：4，他引：38
该文利用海平面气压场资料,计算了1873～1990年的东亚冬季风强度指数,并用滑动t检验和奇异谱分析方法（SSA）对近百年的东亚冬季风的突变性和周期性进行了研究。研究表明:东亚冬季风强度具有显著的年际及年代际变化。当冬季风强时,中国大部分地区温度降低,蒙古高压升高,阿留申低压加深。当冬季风弱时,天气及环流特点几乎与之相反。东亚冬季风存在QBO、LFO和IDO现象,各振荡分量都具有年代际的差别。 相似文献
4.
Experiments of forecasting daily bi-variate index of the tropical atmospheric Madden-Julian Oscillation (MJO) are performed in the context of adaptive filtering prediction models by combining the singular spectrum analysis (SSA) with the autoregressive (AR) methods.the MJO index,a pair of empirical orthogonal function (EOF) time series,called RMM1 and RMM2,predicts by the combined statistical SSA and AR models:firstly,according to the index of historic observation decomposed by SSA and then reconstructed by selecting the first several components based on prominent variance contributions;after that,established an AR prediction model from the composite (scheme A) or built the forecast models for each of these selected reconstructed components,separately (Scheme B).Several experimental MJO index forecasts are performed based on the models.The results show that both models have useful skills of the MJO index forecast beyond two weeks.In some cases,the correlation coefficient between the observed and predicted index series stays above 0.5 in 20 leading days.The SSA-AR model,based on the reconstructed composite series,has better performance on MJO forecast than the AR model,especially for the leading time longer than 5 days.Therefore,if we build a real-time forecast system by the SSA-AR model,it might provide an applicable tool for the operational prediction of the MJO index. 相似文献
5.
Possible role of warm SST bias in the simulation of boreal summer monsoon in SINTEX-F2 coupled model
Susmitha Joseph A. K. Sahai B. N. Goswami Pascal Terray Sebastian Masson J.-J. Luo 《Climate Dynamics》2012,38(7-8):1561-1576
Reasonably realistic climatology of atmospheric and oceanic parameters over the Asian monsoon region is a pre-requisite for models used for monsoon studies. The biases in representing these features lead to problems in representing the strength and variability of Indian summer monsoon (ISM). This study attempts to unravel the ability of a state-of-the-art coupled model, SINTEX-F2, in simulating these characteristics of ISM. The coupled model reproduces the precipitation and circulation climatology reasonably well. However, the mean ISM is weaker than observed, as evident from various monsoon indices. A wavenumber–frequency spectrum analysis reveals that the model intraseasonal oscillations are also weaker-than-observed. One possible reason for the weaker-than-observed ISM arises from the warm bias, over the tropical oceans, especially over the equatorial western Indian Ocean, inherent in the model. This warm bias is not only confined to the surface layers, but also extends through most of the troposphere. As a result of this warm bias, the coupled model has too weak meridional tropospheric temperature gradient to drive a realistic monsoon circulation. This in turn leads to a weakening of the moisture gradient as well as the vertical shear of easterlies required for sustained northward propagation of rain band, resulting in weak monsoon circulation. It is also noted that the recently documented interaction between the interannual and intraseasonal variabilities of ISM through very long breaks (VLBs) is poor in the model. This seems to be related to the inability of the model in simulating the eastward propagating Madden–Julian oscillation during VLBs. 相似文献
6.
Summary Spatio-temporal characteristics of the 25–50-day oscillations are investigated using the empirical orthogonal function (EOF) decomposition and spectral analysis with the Maximum Entropy Method (MEM). Daily pressure values over India during 1978 are used in this study. Power spectra of the temporal coefficients of the two leading EOFs show the existence of a low frequency oscillation with a period range 25–50-day over all India. An analysis using extended empirical orthogonal function (EEOF) indicates North-Eastward propagating 25–50-day mode. The analysis EOF has allowed to establish a relationship between the 25–50-day oscillation and the activity of the summer monsoon. The North-Eastward propagation of this mode is also confirmed by the simple EOF analysis.With 9 Figures 相似文献
7.
Monthly mean surface-air temperatures at 870 sites in the contiguous United States were analyzed for interannual and interdecadal variability over the time interval 1910-87. The temperatures were analyzed spatially by empirical-orthogonal-function analysis and temporally by singularspectrum analysis (SSA). The dominant modes of spatio-temporal variability are trends and nonperiodic variations with time scales longer than 15 years, decadal-scale oscillations with periods of roughly 7 and 10 years, and interannual oscillations of 2.2 and 3.3 years. Together, these modes contribute about 18% of the slower-than-annual United States temperature variance. Two leading components roughly capture the mean hemispheric temperature trend and represent a long-term warming, largest in the southwest, accompanied by cooling of the domain's southeastern quadrant. The extremes of the 2.2-year interannual oscillation characterize temperature differences between the Northeastern and Southwestern States, whereas the 3.3-year cycle is present mostly in the Western States. The 7- to 10-year oscillations are much less regular and persistent than the interannual oscillations and characterize temperature differences between the western and interior sectors of the United States. These continental- or regional-scale temperature variations may be related to climatic variations with similar periodicities, either global or centered in other regions; such variations include quasi-biennial oscillations over the tropical Pacific or North Atlantic and quasi-triennial oscillations of North Pacific sea-surface temperatures.The U.S. Government right to retain a non-exclusive, royalty-free licence in and to any copyright is acknowledged. 相似文献
8.
应用奇异谱分析(SSA)方法和奇异交叉谱分析(SCSA)方法，对全球及南北半球近100多年(1856～1997年)逐月地面气温距平序列中的准两年周期振荡(QBO)的长期演变特征进行诊断分析。结果表明:全球平均气温序列蕴含显著的QBO分量，它们与全球气候系统中其他各个子系统所隐含的QBO信号具有各种耦合对应关系，尤其突出地表现在Nino区海温和以SLP序列为代表的全球大气环流系统中QBO信号的耦合对应关系上。而平均气温的QBO的年代际特征及其变率的阶段性，不但表现在振幅上，而且其位相亦很明显。上述特征在全球、两半球具有明显的差异。 相似文献
9.
Extended empirical orthogonal functions (EEOFs), alternatively known as multi-channel singular systems (or singular spectrum)
analysis (MSSA), provide a natural method of extracting oscillatory modes of variability from multivariate data. The eigenfunctions
of some simple non-oscillatory noise processes are, however, also solutions to the wave equation, so the occurrence of stable,
wave-like patterns in EEOF/MSSA is not sufficient grounds for concluding that data exhibits oscillations. We present a generalisation
of the "Monte Carlo SSA" algorithm which allows an objective test for the presence of oscillations at low signal-to-noise
ratios in multivariate data. The test is similar to those used in standard regression, examining directions in state-space
to determine whether they contain more variance than would be expected if the noise null-hypothesis were valid. We demonstrate
the application of the test to the analysis of interannual variability in tropical Pacific sea-surface temperatures.
Received: 13 September 1995 / Accepted: 4 April 1996 相似文献
10.
The space–time structure of the three-dimensional circulation over the South Asian monsoon region has been studied using the ERA-40 reanalysis of the European Centre for Medium-Range Weather Forecasts. Applying multi-channel singular spectrum analysis on combined daily values of horizontal winds and pressure vertical velocity at ten vertical levels for the period 1958–2001, two leading intraseasonal nonlinear oscillations were extracted. The first oscillation has an average period of 50?days and propagates northeastward from the Indian Ocean to the Indian subcontinent. The second oscillation has a period of 30?days and propagates northwestward from the West Pacific to the Indian region. Both the oscillations exhibit the oscillatory and propagation features at all vertical levels from 1,000 to 100?hPa. The two oscillations correspond well with similar oscillations found in outgoing longwave radiation and precipitation in earlier studies. The wind oscillations also account for the active and break phases of the Indian monsoon. The vertical structures and propagation of specific humidity and temperature are found to be consistent with those of the winds in each oscillation. The structure and movement of regional Hadley and Walker circulations have also been described. The analyses provide further strong evidence for the existence of two distinct monsoon intraseasonal oscillations. 相似文献
11.
12.
夏季西太平洋副热带高压的振荡 总被引：15，自引：7，他引：15
本文用1965年,1976—1985年夏季(6—8月)500hPa逐日西太平洋副热带高压脊线位置的复经验正交函数(CEOF)展开讨论了夏季西太平洋副热带高压的振荡特征。发现西太平洋副热带高压主要存在15—20d以及10d左右的振荡周期,它们一般都是从西太平洋的东部(180°E)向西部(110°E)传播的,其速度为5—7long./d。西太平洋副热带高压10d以下的短周期振荡一般自西(110°E)向东(180°E)传播。其东西部的振荡呈反位相。15—20d周期的振荡能量主要集中在西太平洋东、中部(150—170°E),而10d左右周期的振荡能量主要集中在西太平洋的西部(120一140°E)。一般6月下旬至7月中旬是西太平洋副热带高压的低振荡能量期,而7月中旬以后有一段高振荡能量期。 相似文献
13.
我国近百年气温变化的奇异谱分析 总被引：9，自引：1，他引：8
用奇异谱方法分析我国近百年平均气温的准周期性,结果表明：我国平均气温的年际变化以２～３ａ周期振荡为主,同时１ａ左右的准同期振荡也较强,和同期北半球平均气温的准周期性有差异,不过它们的准１ａ周期振荡随时间的阶段性变化特征非常相似。将我国大致分成７个区域,对７个区域代表站气温进行奇异谱分析,结果表明：各区气温的准周期振荡及其随时间的变化互不相同。华北、东北、西北、和青藏高原４区气温以１ａ周期振荡最为显 相似文献
14.
利用奇异谱分析方法（SSA）分析了1975年1月1日至12月31日北半球30hPa高度场变化特征，结果发现:平流层低层大气除了年变化及季节变化趋势外，还存在明显的季节内振荡，最显著的周期为20～60天；在持续性异常多发地区，30hPa高度场变化中20～40天周期振荡占优势，而在其它一些地区则盛行40～60天周期振荡；对流层持续性异常主要同对流层高度场的20～40天振荡有关，并可能通过这种周期振荡同平流层低层相同周期的振荡的相互作用影响平流层低层大气季节内变化。 相似文献
15.
用1979/1980～2017/2018年冬季逐日长江下游气温资料研究长江下游冬季低温日数与温度低频振荡的联系.结果表明,冬季长江下游逐日气温存在较显著的季节内振荡周期(15～25 d、25～40 d和50～70 d振荡),其中与12～2月低温日数关系最密切的是25～40 d振荡.基于2001～2018年逐日长江下游实... 相似文献
16.
Intraseasonal oscillations in 15 atmospheric general circulation models: results from an AMIP diagnostic subproject 总被引：16，自引：1，他引：16
J. M. Slingo K. R. Sperber J. S. Boyle J.-P. Ceron M. Dix B. Dugas W. Ebisuzaki J. Fyfe D. Gregory J.-F. Gueremy J. Hack A. Harzallah P. Inness A. Kitoh W. K.-M. Lau B. McAvaney R. Madden A. Matthews T. N. Palmer C.-K. Parkas D. Randall N. Renno 《Climate Dynamics》1996,12(5):325-357
17.
By using the power spectrum analysis, the interannual variation of medium-range oscillation charac-teristics in the upper troposphere over the subtropical region in China during June-August, 1966－1981 is studied. The quasi-two and quasi-one week oscillations are the two major oscillations generally existing in the subtropical region, and their intensities have obvious quasi-triennial variation period. These medium-range oscillation characteristics are closely related to the South Asian high, and in some degree to the summer precipitation in China. The quasi-two week oscillation is probably a display of the inherent oscillation of the south Asian high itself, and the quasi-one week oscillation is probably that of the forced oscillation from westerly disturbances. 相似文献
18.
Masakazu Yoshimori Christoph C. Raible Thomas F. Stocker Manuel Renold 《Climate Dynamics》2010,34(1):101-121
The significance of the Atlantic meridional overturning circulation (MOC) for regional and hemispheric climate change requires
a complete understanding using fully coupled climate models. Here we present a persistent, decadal oscillation in a coupled
atmosphere–ocean general circulation model. While the present study is limited by the lack of comparisons with paleo-proxy
records, the purpose is to reveal a new theoretically interesting solution found in the fully-coupled climate model. The model
exhibits two multi-century-long stable states with one dominated by decadal MOC oscillations. The oscillations involve an
interaction between anomalous advective transport of salt and surface density in the North Atlantic subpolar gyre. Their time
scale is fundamentally determined by the advection. In addition, there is a link between the MOC oscillations and North Atlantic
Oscillation (NAO)-like sea level pressure anomalies. The analysis suggests an interaction between the NAO and an anomalous
subpolar gyre circulation in which sea ice near and south of the Labrador Sea plays an important role in generating a large
local thermal anomaly and a meridional temperature gradient. The latter induces a positive feedback via synoptic eddy activity
in the atmosphere. In addition, the oscillation only appears when the Nordic Sea is completely covered by sea ice in winter,
and deep convection is active only near the Irminger Sea. Such conditions are provided by a substantially colder North Atlantic
climate than today. 相似文献
19.
两个大气环流模式SAMIL和BCC_AGCM对北半球冬季极涡振荡的模拟对比 总被引：1，自引：1，他引：1
基于与NCEP再分析资料的比较, 本文利用大气环流模式SAMIL和北京气候中心大气环流模式BCC_AGCM的1950～1999年的AMIP试验模拟数据, 对北半球冬季环流及平流层极涡振荡的模拟性能进行了评估分析。结果表明两个模式都可以再现北半球环流基本型以及环流振荡的主导模态。对冬季气候平均态的模拟, 两个模式模拟的热带—热带外温度梯度均偏大, 极夜急流偏强, 极涡偏冷偏强;100～20 hPa平均位势高度场谐波分析表明两个模式模 拟的行星波偏弱;气候平均的10 hPa极夜急流均存在1个月的季节漂移, 200 hPa副热带西风急流较NCEP偏弱。两个模式模拟的环流变化的主导模态均代表极涡振荡, SAMIL极涡振荡的强度大于BCC_AGCM, BCC_AGCM极涡振荡的频率要高于SAMIL。连续功率谱分析表明, NCEP资料中极涡振荡存在4.6个月的显著周期, 相应地, SAMIL中为5.5个月的显著周期, BCC_AGCM中为4.8个月。NCEP资料中的极涡振荡主要发生在12～3月, SAMIL模拟的极涡振荡主要发生在2～3月, BCC_AGCM模拟的极涡振荡主要发生在2～4月。 相似文献
20.
本文用多维谱分析的方法，研究了1984年夏季张掖地区辐射参数的中短期和超短期振荡特征。1984年夏季，张掖地区辐射等参数存在着3—5天的中短期振荡及30分钟、50分钟和80分钟的超短期振荡。准3天振荡主要存在于热力边界层，振荡是由西向东传播的，影响高度大致为400 hPa。超短期振荡强度有着明显的日际变化，其变化周期也大致为3—5天。在大气中各种时间尺度的振荡之间存在着某种联系。准3天振荡可能是青藏高原地面热力扰动影响的一种反映；准30分钟的超短期振荡强度与天气系统的关系不明显，而与热力状况及主要云状却有一定的关系。 相似文献