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1.
Principal component or Empirical Orthogonal Function (EOF) analysis is applied to tsunameter records by treating them as two-dimensional signals, where the second dimension is created by breaking a single time series into cycles and treating the cycle number as a second dimension. Under certain conditions, principal components calculated from different records are shown to determine the same functional space. Signal decomposition into pre-calculated principal components is used to predict or extract the tidal component of a record. This work shows that EOF processing allows for short-term tidal predictions at tsunami buoy locations with the precision of more advanced methods and with minimal a priori knowledge about tidal dynamics. Also shown is that filtering in EOF domain is sensitive to the non-tidal component of a record and therefore presents a tool for early tsunami detection and quantification. 相似文献
2.
Three 40-member ensemble experiments and a 700?year control run are used to study initial value predictability in the North Pacific in Community Climate System Model version 3 (CCSM3). Our focus is on the leading two empirical orthogonal functions (EOFs) of subsurface temperature variability, which together produce an eastward propagating mode. Predictability is measured by relative entropy, which compares both the mean and spread of predictions of ensembles to the model??s climatological distribution of states. Despite the fact that EOF1, which is structurally similar to the observational Pacific Decadal Oscillation (PDO), has pronounced spectral peaks on decadal time scales, its predictability is less than 6?years. Additional predictability resides in the tendency of EOF1 to evolve to EOF2, primarily through simple advective processes. The propagating mode represented by the combination of EOF1 and EOF2 is predictable for about a decade. Information in both the mean and spread of predicted ensembles contribute to this predictability. Among the leading 15 EOFs, EOF1 is the least predictable mode in terms of the rate at which the corresponding principal component disperses in the ensemble experiments. However, it can produce enhanced predictability of the whole system by inducing EOF2, which is one of the two EOFs with the slowest dispersion rate. The first two EOFs can also enhance the ensemble mean (or ??signal??) component of predictability of the entire system. For typical amplitude initial states, this component contributes to predictability for about 6?years. For initial states with unusually high amplitude projections onto these two EOFs, this contribution can last much longer. The major findings from the three ensemble experiments are replicated and generalized when the initial condition predictability for each of many hundreds of different initial states is estimated. These estimates are derived from the behavior of a linear inverse model (LIM) that is based on the intrinsic variability present in the control run. 相似文献
3.
Tides affect transport and mixing in the Indonesian Seas, impacting the throughflow and the return flow of the global thermohaline circulation. In a previous study, barotropic and baroclinic tides were simulated for the Indonesian Seas at 5 km resolution in order to characterize the tides of the region and to identify and quantify locations of tidal mixing. Baroclinic tidal velocities exceeded barotropic velocities except in shallow regions and their variability was on smaller scales. Model results agreed reasonably with observations and are consistent with the resolution. However, only four mooring locations were available for comparison. The new International Nusantara Stratification (INSTANT) data set enables a more comprehensive comparison. With the exception of Lombok Strait, the model replicated the observed INSTANT velocity spectra, falling within the 90% confidence limits of the observed spectra, both in regions of high and low baroclinic tidal activity for the band of frequencies from 0.02 cph to 0.33 cph (periods of 50–3 h, respectively), which includes the major semidiurnal and diurnal tides and several of their first harmonics. The model overestimated the semidiurnal baroclinic tides in the narrow Lombok Strait, which is not well resolved in the model. Comparisons of vertical profiles of the major axes of the tidal ellipses at the mooring sites generally reproduced the vertical pattern, although there were exceptions, such as Lombok and Ombai Straits. Rms differences between the model estimates and hourly observations for the major axes of the tidal ellipses were typically 1–8 cm s−1 in regions of high tidal activity, 1–5 cm s−1 in regions of low tidal activity, and 1–20 cm s−1 for the semidiurnal tides in Lombok and Ombai Straits. Rms errors of 1–6 cm s−1 are typical in regions of moderate baroclinic tidal activity at this model resolution (5 km). Many of the larger rms differences result from vertical discrepancies in the depths of the internal tidal beams. The local nature of the internal tides generation and beam propagation results in large differences from small vertical shifts in the beams or generation due to topographic differences between the model topography and the actual topography. In addition, the moorings experienced severe blowdown. The blowdown adds uncertainty to the depths of the instruments and introduces errors in the observational tidal analysis in magnitude of the tidal constituents, both of which contribute to rms differences. Tidal mixing was found to occur in intense local regions with strong internal tidal shear. The local regions of mixing were typically along the bottom in steep slopes and over sills. In conclusion, the tidal model was found to reproduce the kinetic energy distribution and transfer of energy from tides to other frequencies in the Indonesian Seas and to roughly replicate the observed structure and magnitude of the tidal currents. Improvements in the tidal simulations in reproducing observations are expected with increased resolution. 相似文献
4.
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
5.
Towards constraining climate sensitivity by linear analysis of feedback patterns in thousands of perturbed-physics GCM simulations 总被引：2，自引：1，他引：1
Benjamin M. Sanderson C. Piani W. J. Ingram D. A. Stone M. R. Allen 《Climate Dynamics》2008,30(2-3):175-190
A linear analysis is applied to a multi-thousand member “perturbed physics" GCM ensemble to identify the dominant physical
processes responsible for variation in climate sensitivity across the ensemble. Model simulations are provided by the distributed
computing project, climate prediction.net . A principal component analysis of model radiative response reveals two dominant independent feedback processes, each
largely controlled by a single parameter change. The leading EOF was well correlated with the value of the entrainment coefficient—a
parameter in the model’s atmospheric convection scheme. Reducing this parameter increases high vertical level moisture causing
an enhanced clear sky greenhouse effect both in the control simulation and in the response to greenhouse gas forcing. This
effect is compensated by an increase in reflected solar radiation from low level cloud upon warming. A set of ‘secondary’
cloud formation parameters partly modulate the degree of shortwave compensation from low cloud formation. The second EOF was
correlated with the scaling of ice fall speed in clouds which affects the extent of cloud cover in the control simulation.
The most prominent feature in the EOF was an increase in longwave cloud forcing. The two leading EOFs account for 70% of the
ensemble variance in λ—the global feedback parameter. Linear predictors of feedback strength from model climatology are applied
to observational datasets to estimate real world values of the overall climate feedback parameter. The predictors are found
using correlations across the ensemble. Differences between predictions are largely due to the differences in observational
estimates for top of atmosphere shortwave fluxes. Our validation does not rule out all the strong tropical convective feedbacks
leading to a large climate sensitivity. 相似文献
6.
Winter precipitation over Central Asia and the western Tibetan Plateau (CAWTP) is mainly a result of the interaction between the westerly circulation and the high mountains around the plateau. Empirical Orthogonal Functions (EOFs), Singular Value Decomposition (SVD), linear regression and composite analysis were used to analyze winter daily precipitation and other meteorological elements in this region from 1979 to 2013, in order to understand how interactions between the regional circulation and topography affect the intraseasonal variability in precipitation. The SVD analysis shows that the winter daily precipitation variability distribution is characterized by a dipole pattern with opposite signs over the northern Pamir Plateau and over the Karakoram Himalaya, similar to the second mode of EOF analysis. This dipole pattern of precipitation anomaly is associated with local anomalies in both the 700 hPa moisture transport and the 500 hPa geopotential height and is probably caused by oscillations in the regional and large-scale circulations, which can influence the westerly disturbance tracks and water vapor transport. The linear regression shows that the anomalous mid-tropospheric circulation over CAWTP corresponds to an anti-phase variation of the 500 hPa geopotential height anomalies over the southern and northern North Atlantic 10 days earlier (at 95% significance level), that bears a similarity to the North Atlantic Oscillation (NAO). The composite analysis reveals that the NAO impacts the downstream regions including CAWTP by controlling south-north two branches of the middle latitude westerly circulation around the Eurasian border. During the positive phases of the NAO, the northern branch of the westerly circulation goes around the northwest Tibetan Plateau, whereas the southern branch encounters the southwest Tibetan Plateau, which leads to reduced precipitation over the northern Pamir Plateau and increased precipitation over the Karakoram Himalaya, and vice versa. 相似文献
7.
8.
经验正交函数展开精度的稳定性研究 总被引：7，自引：3，他引：7
在文献[1]中,我们已从理论和数值模拟两个方面研究了用经验正交函数作基函数缩减气候数值模式自由度的可行性与有效性。用理论模型作数值试验的结果是令人满意的,应用于实际气候数值模拟,一个还需考虑的关键问题是大气外强迫等各种因子变化允许的范围内,对实际资料作EOF展开的稳定性问题。本文分别用1951—1984年500 hPa月平均高度距平场资料,1966—1975年500 hPa候平均高度距平场资料,1965—1978年夏季500 hPa逐日高度距平场资料作EOF展开,并提出了经验正交函数展开精度稳定性的判断方法,旨在证明实际资料EOF展开在大气外强迫等各种因子变化的允许范围内是稳定的,以便为我们用实际资料的经验正交函数作基函数建立一个合理的简化动力模型提供坚实的资料基础。 相似文献
9.
《大气与海洋》2013,51(3):217-231
Abstract An intermediate coupled model of the tropical Pacific ocean‐atmosphere system was reduced by projecting the non‐linear model onto a truncated basis set of its own empirical orthogonal functions (EOFs). For moderate coupling strengths, the simulated El Niño/Southern Oscillation (ENSO) variability consists of a dominant quasi‐quadrennial mode with a period of approximately four years and a smaller quasi‐biennial mode at a period of approximately two years. In the absence of a seasonal cycle, the leading two EOFs capture the dynamics of the leading interannual mode, with a further two EOFs being required to capture the secondary oscillation. The presence of seasonal forcing increases the EOF requirement by two, the leading pair of EOFs being dominated by the annual cycle. Normal mode analysis of the reduced models indicates that the quasi‐biennial mode manifests itself, even though it is linearly stable, by non‐linear coupling to the quasi‐quadrennial mode. The nonlinearity does not produce the quasi‐biennial signal unless the spatial degrees of freedom associated with the linear quasi‐biennial mode are present. Other linearly stable modes also couple non‐linearly to the leading interannual mode and to the seasonal cycle, but the quasi‐biennial mode is favoured over other, less‐damped linear modes because of its proximity to a multiple of the quasi‐quadrennial frequency. 相似文献
10.
Robust GEFA Assessment of Climate Feedback to SST EOF Modes 总被引：2，自引：0，他引：2
Atmospheric response to SST variability was estimated using generalized equilibrium feedback analysis (GEFA) in the SST EOF space with synthesis data from an idealized climate model. Results show that the GEFA atmospheric response to the leading SST EOF modes is much more accurate and robust than the GEFA feedback matrix in physical space. Therefore, GEFA provides a practical method for assessing atmospheric response to large-scale SST anomalies in terms of the leading EOFs. 相似文献
11.
We describe the use of bivariate three-dimensional empirical orthogonal functions (EOFs) in characterising low frequency variability of the Atlantic thermohaline circulation (THC) in the Hadley Centre global climate model, HadCM3. We find that the leading two modes are well correlated with an index of the meridional overturning circulation (MOC) on decadal timescales, with the leading mode alone accounting for 54% of the decadal variance. Episodes of coherent oscillations in the sub-space of the leading EOFs are identified; these episodes are of great interest for the predictability of the THC, and could indicate the existence of different regimes of natural variability. The mechanism identified for the multi-decadal variability is an internal ocean mode, dominated by changes in convection in the Nordic Seas, which lead the changes in the MOC by a few years. Variations in salinity transports from the Arctic and from the North Atlantic are the main feedbacks which control the oscillation. This mode has a weak feedback onto the atmosphere and hence a surface climatic influence. Interestingly, some of these climate impacts lead the changes in the overturning. There are also similarities to observed multi-decadal climate variability. 相似文献
12.
Abstract The relationship between sea surface temperature (SST) and rainfall index anomalies over sub‐Saharan Africa for the 15‐year period, 1970–84, has been examined. The objectively analysed monthly mean SST data were used for the global oceans between 40°S and 60°N. The rainfall data consist of annual mean rainfall indices for the Sahel and Soudan belts over north Africa. An Empirical Orthogonal Function analysis of the SST data has been carried out for the Atlantic, Indian and global ocean regions. The results show that the most dominant eigenmode, EOF1, is characterized by warming over the central eastern Pacific, cooling over the eastern mid‐latitude Pacific and warming over the entire Atlantic and Indian ocean basins. The second EOF for the Atlantic Ocean SST analysis shows a dipole (north‐south see‐saw) pattern. The third EOF for the Atlantic SST analysis has the same sign over the entire Atlantic basin. Global SST EOF2 and EOF3 correspondió Atlantic SST EOF3 and EOF2, respectively. The correlation between the sub‐Saharan annual rainfall index, which mainly represents the summer season rainfall from June to September, and SST EOFs shows that EOF1 has statistically significant monthly correlations for the Sahel and Soudan regions and that the warm El Niño‐like phases of SST EOF1 correspond to drought conditions. This result suggests that the large‐scale SST anomalies may be responsible for a significant component of the observed vacillation of sub‐Saharan rainfall. Some preliminary GLA GCM simulation results that support the above findings are also presented. 相似文献
13.
利用EOF相空间分析东亚梅雨旱涝长期过程的初步研究 总被引：11，自引：1，他引：11
利用非线性动力学中的相空间概念,分析了梅雨旱涝3～5年循环的长期过程.对全球热带850hPa的纬向风场距平所作的EOF,第1特征向量显示了Walker环流异常在赤道球圈上的分布;第2特征向量主要显示热带-副热带之间的环流异常的经向分布.在第1时间系数和第2时间系数所定义的2维相空间中,由相轨线分析,得到梅雨涝年主要集中于第2象限,而旱年则相对多在第4象限.说明梅雨旱涝年际变异的主导模态和热带大气环流的主要特征向量有着密切的关联.它们显示了以3～5年时间尺度的大气环流演变的长期特征性过程. 相似文献
14.
Long-Term Trend of Temperature Derived by Statistical Downscaling Based on EOF Analysis 总被引：1，自引：0，他引：1 
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下载免费PDF全文 This study analyzes the ability of statistical downscaling models in simulating the long-term trend of temperature and associated
causes at 48 stations in northern China in January and July 1961–2006. The statistical downscaling models are established
through multiple stepwise regressions of predictor principal components (PCs). The predictors in this study include temperature
at 850 hPa (T850), and the combination of geopotential height and temperature at 850 hPa (H850+T850). For the combined predictors,
Empirical Orthogonal Function (EOF) analysis of the two combined fields is conducted. The modeling results from HadCM3 and
ECHAM5 under 20C3M and SERS A1B scenarios are applied to the statistical downscaling models to construct local present and
future climate change scenarios for each station, during which the projected EOF analysis and the common EOF analysis are
utilized to derive EOFs and PCs from the two general circulation models (GCMs). The results show that (1) the trend of temperature
in July is associated with the first EOF pattern of the two combined fields, not with the EOF pattern of the regional warming;
(2) although HadCM3 and ECHAM5 have simulated a false long-term trend of temperature, the statistical downscaling method is
able to well reproduce a correct long-term trend of temperature in northern China due to the successful simulation of the
trend of main PCs of the GCM predictors; (3) when the two-field combination and the projected EOF analysis are used, temperature
change scenarios have a similar seasonal variation to the observed one; and (4) compared with the results of the common EOF
analysis, those of the projected EOF analysis have been much more strongly determined by the observed large-scale atmospheric
circulation patterns. 相似文献
15.
实际预报可预报性的时空依赖性分析 总被引：4，自引：1，他引：4
本文利用国家气象中心1990年1月1日至1992年2月29日的1～5 d、500 hPa高度场业务预报结果研究了不同球谐函数谱分量和经验正交函数(EOF)谱分量的可预报性。对球谐函数谱分量的研究表明可预报性并不是随着空间尺度的增加呈现单调的递减关系，主要表现为在总波数n等于5附近具有最大可预报性。可预报性主要依赖于总波数n，经卷大圆上的波数和纬向圆周上的波数对可预报性具有完全相同的重要意义。对EOF谱分量的分析表明，随着EOF指数(即序号数)的增大，可预报性依次减小。从EOF和球谐函数的关系发现前几个EOF分量正是对应着最可预报的球谐函数分量。进一步分析表明，最可预报的分量对应大气运动的慢变流型。这些结果对如何使用数值预报产品以及如何进行延伸预报具有重要意义。 相似文献
16.
A stochastic model of SST for climate simulation experiments 总被引：1，自引：0，他引：1
This study describes the implementation of a statistical method to simulate a multi-century sequence of global sea surface
temperature (SST) fields. A multi-variable auto-regressive (AR) model is trained on the observed time series of SST from the
data set compiled at the Hadley Centre (GISST 2.0). To reduce the dimensionality of the model, the stochastic process is in
practice fitted to empirical orthogonal function (EOF) time coefficients of the SST series, retaining the first 14 EOFs. Selected
lag cross-covariances among the EOF time series are retained, based on the structure of the cross-correlation matrix and lags
up to 64 months are included. Though the resulting system is quite large (a 14-dimensional AR process, with 400 parameters
to be determined) the calculation is possible and a stable process is obtained. The process can then be used to investigate
some statistical properties of the SST data set and to generate synthetic SST data that could be used in very long numerical
experiments with atmospheric or ocean models in which only the main features of the observed statistics of the SST must be
retained. Results indicate that the synthetic SST data set seems to be of usable quality as boundary condition for the atmosphere
or the ocean in climate experiments. Analysis of extreme events and extreme decades in the synthetic SST data confirms the
exceptional character of the 1980s, but also provides circumstantial evidence that the 1980s were indeed within the limits
of the statistics of the previously observed record.
Received: 6 August 1996 / Accepted: 29 September 1997 相似文献
17.
On the basis of the 1950–2001 NCEP reanalysis data, space-time variability of the surface pressure (SP), surface air temperature (SAT), and precipitation fields in Eurasia is studied in connection with the 1976–1977 climate shift. The effect of the shift manifests itself in the change in the space-time structure of empirical orthogonal functions (EOFs) in all these fields from September to April. For SP and SAT, during this period, only two first EOFs are stable with respect to the climate shift. Also, for SAT and SP, the second EOFs are stable from November to April and from September to December, respectively. For the precipitation field, even the first EOFs are unstable during the whole period, with the exception of January and February. Instability with respect to the climate shift appears first in change in the EOF spatial pattern of the fields. Stability of the first modes of the Eurasian meteorological fields to the 1976–1977 climate shift is caused by a relative stability of the North Atlantic Oscillation, which explains up to 70 and 30% of variance of the first and second EOFs, respectively, of the hydrometeorological fields in the region. 相似文献
18.
EOF/PCA诊断气象变量场问题的新探讨 总被引：13，自引：3，他引：10
进一步论证了经验正交函数/主分量分析(EOF/PCA)在气象变量场诊断中的物理内涵,证明基于EOF/PCA的R型和Q型展开,可描述为气象变量场主要振荡型分解和主要空间分布型分解两种方案.前者表明,气象变量场的准周期振荡可分解为各主分量的周期振荡,它们各自等价于不同网格点(或站点)以其载荷为权重的迭加周期振荡,因此,气象变量场准周期振荡可视为来自不同周期源(网格点或站点)的准周期振荡逐层叠加的结果;后者表明,气象变量场的水平空间分布可视为各种主要空间分布型的叠加,而Q型展开才是对各种主要空间分布型的正交分解.由此深化了EOF/PCA气象变量场诊断的物理内涵. 相似文献
19.
The character of turbulent overturns in a weakly stratified deep-sea is investigated in some detail using 144 high-resolution temperature sensors at 0.7 m intervals, starting 5 m above the bottom. A 9-day, 1 Hz sampled record from the 912 m depth flat-bottom (<0.5% bottom-slope) mooring site in the central-north Alboran Sea (W-Mediterranean) demonstrates an overall conservative temperature range of only 0.05 °C, a typical mean buoyancy period as large as 3 h and a 1 Hz-profile-vertically-averaged turbulence dissipation rate maximum of only 10−8 m2 s−3. Nonetheless, this ‘boundary layer’ varies in height between <6 and >104 m above the bottom and is thus not homogeneous throughout; the temperature variations are seldom quiescent and are generally turbulent in appearance, well exceeding noise levels. The turbulence character is associated with small-scale internal waves; examples are found of both shear- and convection-driven turbulence; particular association, although not phase-locked, is found between turbulence variations and tidal rather than with inertial motions; the mean buoyancy frequency of a few times the inertial frequency implies the importance of ‘slantwise convection’ in the direction of the earth rotational vector rather than in the direction of gravity. Such convection is observed both in near-homogeneous and weakly stratified form. 相似文献
20.
Direct velocity measurements from 2004 through 2006 confirm the eastward flowing surface South Java Current (SJC) and its deeper Undercurrent (SJUC) crosses the Savu Sea to reach Ombai Strait, a main outflow portal of the Indonesian Throughflow (ITF). The extension of the South Java Current system into Ombai Strait was hinted at by earlier measurement and modeling studies, but the 3-year velocity time series from two moorings in Ombai Strait clearly show separate distinct cores of flow in the SJC and SJUC. The deeper SJUC is driven by Kelvin waves forced by intraseasonal and semi-annual winds in the equatorial Indian Ocean and, when present, is observed across the entire strait. Eastward flow in the surface SJC is near year-round, although it appears that the mechanisms responsible for this flow differ throughout the year. Both the wind-driven Ekman flow during the northwest monsoon and the strongest semi-annual Kelvin waves that have surface signatures can result in eastward surface layer flow across the entire strait. In contrast, during the southeast monsoon the SJC has a subsurface maximum eastward flow at 50–100 m depth in the northern part of Ombai Strait, while the westward ITF is at an annual maximum at the surface in the southern part of the strait. Surface temperature maps suggest the presence of a front during the southeast monsoon that seems to trap the SJC to within ∼10–15 km of the northern boundary of Ombai Strait. The SJC and the frontal location are related to a complex interplay between local wind-driven Ekman dynamics, the strong ITF flow and topography. Significant energy is found at short intraseasonal time scales (20–60 days) in the along-strait flow that is probably related to the short duration westerly wind bursts that drive the Kelvin waves into Ombai Strait. There is a distinct lack of energy at longer intraseasonal time scales (60–90 days) that is likely attributable to interannual climate variability. 相似文献