共查询到20条相似文献，搜索用时 34 毫秒
1.
Almost all climate time series have some degree of nonstationarity due to external forces of the observed system. Therefore, these external forces should be taken into account when reconstructing the climate dy- namics. This paper presents a novel technique in predicting nonstationary time series. The main difference of this new technique from some previous methods is that it incorporates the driving forces in the pre- diction model. To appraise its effectiveness, three prediction experiments were carried out using the data generated from some known classical dynamical models and a climate model with multiple external forces. Experimental results indicate that this technique is able to improve the prediction skill effectively. 相似文献
2.
Identifying Nonstationarity in Turbulence Series 总被引：1，自引：1，他引：0
Edgar L Andreas Cathleen A. Geiger George Treviño Kerry J. Claffey 《Boundary-Layer Meteorology》2008,127(1):37-56
Because of rapid forcing by varying cloud and sky conditions, turbulence time series collected in the atmospheric surface
layer over land may often be nonstationary. The meteorological community, however, has no consensus definition of what nonstationarity
is and, thus, no consensus method for how to identify it. This study, therefore, adopts definitions for first-order and second-order
stationarity taken from the time series analysis literature and implements new analysis techniques and probabilistic tests
to quantify first-order and second-order nonstationarity. First-order nonstationarity manifests as a change in the series
mean; second-order nonstationarity, as a change in the variance. The analysis identifies nonstationarity in surface-level
turbulent temperature and water vapour series collected during two sample days with solar forcing influenced by cirrus and
cirrostratus clouds, but that nonstationarity is not as severe as expected despite the rapid thermal forcing by these clouds.
On the other hand, even with negligible cloud forcing, both sample days exhibited severe nonstationarity at night. 相似文献
3.
The Prediction of Non-stationary Climate Series Based on Empirical Mode Decomposition 总被引：1，自引：0，他引：1
This paper proposes a new approach which we refer to as ``segregated
prediction" to predict climate time series which are nonstationary. This
approach is based on the empirical mode decomposition method (EMD), which
can decompose a time signal into a finite and usually small number of basic
oscillatory components. To test the capabilities of this approach, some
prediction experiments are carried out for several climate time series. The
experimental results show that this approach can decompose the
nonstationarity of the climate time series and segregate nonlinear
interactions between the different mode components, which thereby is able to
improve prediction accuracy of these original climate time series. 相似文献
4.
本文运用非线性交叉预报误差的新方法,使用GMS-5的TBB(亮温)非线性时间序列资料,对湖北武汉“98.7”特大暴雨进行了定常与非定常特征计算和判断分析,与实际降雨的变化趋势十分吻合。 相似文献
5.
气候系统具有非平稳特征,根本原因在于其外强迫随时间发生改变,因此外部驱动力的分析对于理解气候系统的动力学特征至关重要,而如何有效提取系统外部驱动信息是一个亟待解决的前沿科学问题。最近几年,在生物神经学领域中应用的一种提取非平稳信号中外强迫信息的方法——慢特征分析法(Slow Feature Analysis,SFA),在气象领域中也得到了初步成功的尝试,结果显示出此方法对气候系统的外强迫信息分析及有关动力学机制的探究有较好的应用前景。本文主要介绍SFA方法的理论思想及实施步骤,并通过一个理想的非平稳时间序列检验其提取外强迫信息的能力,结果证明在衰减的Logistic模型中,可利用SFA算法提取出模型中的外强迫,且与真实外强迫的相关系数可达0.99;此外,还介绍将该方法应用于Arosa臭氧时间序列,分析其提取的外强迫信息的动力学特征;并介绍了在气候时间序列建模中引入外强迫因子的预测效果。 相似文献
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7.
Record-breaking extreme temperatures have been measured in the last two decades all over Turkey, with recent studies detecting positive trends in extreme temperature time series. In this study, nonstationary extreme value analysis was performed on extreme temperature time series obtained from fifty stations scattered over the seven geographical regions of Turkey. Basic characterization of the data set was defined through outlier detection, homogeneity, trend detection, and stationarity tests. Trend-including non-stationary extreme temperature time series were analyzed with non-stationary Generalized Extreme Value distribution. Three main physical drivers were considered as the leading causes that trigger the observed trends in extreme temperatures over Turkey: time, teleconnection patterns of the Arctic Oscillations, and those of the North Atlantic Oscillations. The results showed that most of the absolute annual minimum and maximum temperature time series are inhomogeneous while the possible breakpoints date back to the1970s and 1990s, respectively. More than half of the absolute annual maximum time series (26/50 and many of the absolute annual minimum time series (21/50) showed a positive trend. No negative trend was detected in the extreme temperature time series. Based on the frequency analysis of the 21 annual maximum time series, the non-stationary estimations of 50-year return levels were detected to be higher than in the stationary model (between 0.44 °C and 3.73 °C). The return levels in 15 of the 20 minimum temperature time series increased from 0.11 °C up to 12.28 °C. Elevation increases the nonstationarity impact on absolute minimum temperatures and decreases it on absolute maximums. The findings in this study indicate that the consideration of non-stationarity in extreme temperature time series is a necessity during return level estimations over the study area. 相似文献
8.
Nicholas C. Matalas 《Climatic change》1997,37(1):89-101
Hydrologic trends, real (physical) or perceived (statistical), suggest that water management be predicated on the assumption of hydrologic nonstationarity. The assumption leaves open the question to what extent will the "trends" be sustained locally and regionally over the future 25, 50 or 100 years corresponding to the economic time horizons of water projects. Whether hydrologic trends are real or perceived, record events of hydrologic extremes, floods and droughts, will be broken with exceedingly high probabilities over the economic lives of water projects. Before the assumption of hydrologic nonstationarity is accepted, the ability to cope with the uncertain impacts of global warming on water management via the operational assumption of hydrologic stationarity should be carefully examined. In the absence of strong physical evidence, trends cannot be unequivocally distinguished from slow oscillations. Slow oscillations can be mimicked by persistence in stationary processes. It is time to examine the relative merits of the assumptions of stationarity and nonstationarity in the operational context of water management. The strategy of wait-and-see, i.e. delaying the making of important, expensive and essentially irreversible capital investments, could served water managers well in coping with the uncertainties regarding climate change. 相似文献
9.
Turbulence data collected over a total of 25 days during two summers are used to describe processes responsible for the nonstationarity
of turbulent sensible heat fluxes at Summit, Greenland. A stationarity test shows that about 40% of the data are classified
as nonstationary. Three main factors are explored to account for the large fraction of nonstationary runs: (1) intermittency
of turbulence in stable conditions, (2) changes in net all-wave radiation in response to cloud forcing, and (3) diurnal trends
in stability. A classification procedure that accounts for the intermittent nature of turbulence shows that during stable,
nonstationary conditions 50% of the total sensible heat flux is realized in 22% of the sampling time. Intermittency often
occurs at Summit during periods characterized by weak and irregular horizontal winds in combination with strong stability.
Rapid changes in net all-wave radiation in response to cloud forcing results in nonstationarity during unstable conditions.
Between 0930–1130 and 1900–1930 UTC turbulent heat fluxes are not only small in magnitude but also typically change sign,
with nonstationarity during these periods often as high as 65%. These results should help resolve some of the present uncertainties
in obtaining reliable fluxes at this site, in particular under stable atmospheric conditions. 相似文献
10.
L. Mahrt 《Boundary-Layer Meteorology》2007,125(2):245-264
Extensive eddy-correlation datasets are analyzed to examine the influence of nonstationarity of the mean flow on the flux–gradient
relationship near the surface. This nonstationarity is due to wavelike motions, meandering of the wind vector, and numerous
unidentified small-scale mesoscale motions. While the data do not reveal an obvious critical gradient Richardson number, the
maximum downward heat flux increases approximately linearly with increasing friction velocity for significant stability.
The largest of our datasets is chosen to more closely examine the influence of stability, nonstationarity, distortion of the
mean wind profile and self-correlation on the flux-gradient relationship. Stability is expressed in terms of z/L, the gradient Richardson number or the bulk Richardson number over the tower layer. The efficiency of the momentum transport
systematically increases with increasing nonstationarity and attendant distortion of the mean wind profile. Enhancement of
the turbulent momentum flux associated with nonstationarity is examined in terms of the nondimensional shear, Prandtl number
and the eddy diffusivity. 相似文献
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Thomas Foken 《Boundary-Layer Meteorology》2006,119(3):431-447
In weak wind stable conditions, eddy-correlation fluxes calculated using conventional averaging times of 5 min or longer to define the perturbations are severely contaminated by poorly sampled mesoscale motions. A method is developed to identify the averaging time for each individual data record that captures the turbulence while excluding most of the mesoscale motions. The method is based on multiresolution decomposition of the heat flux, and provides an objective procedure for selecting the averaging time for calculating eddy-correlation fluxes. Eddy-correlation data collected in weak turbulence conditions over grass, snow, a pine forest and the ocean are used to demonstrate the approach.When the small-scale turbulence and mesoscale motions are clearly separated by a gap region in the heat flux cospectra, the variable window width reduces the influence of nonstationarity by more effectively filtering out mesoscale motions compared to traditional methods using constant averaging time. For records where turbulence and mesoscale motions overlap in scale, the method is not well posed, although such records occur infrequently for our datasets. These ambiguous cases correspond to significant nonstationarity at scales that overlap with turbulence scales. The improved turbulence fluxes calculated with the proposed method are the appropriate fluxes for evaluating flux-gradient relationships and Monin–Obukov similarity theory for developing improved model parameterizations of turbulence for weakly turbulent flows 相似文献
13.
Analysis of Stationary-Wave Nonstationarity in the Northern Hemisphere 500-hPa Height Field 
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下载免费PDF全文 ZHOU Guohu WANG Panxing SHI Ning LI Qiaoping SHE Gaojie 《Acta Meteorologica Sinica》2010,24(3):287-296
In this paper, the concept of stationary-wave nonstationarity is presented and elucidated in the framework of the Lorenz circulation decomposition. This concept indicates the relative magnitude of the zonal nonuniform abnormity to the intensity of stationary waves on the monthly mean scale. Based on the Lorenz circulation decomposition, the nonstationarity degree Ius(Ilus) of the global (local) stationary waves is defined, and then used to analyze the stationary-wave nonstationarity at 30° 60°N, where the intensity of stationary waves at 500 hPa in the Northern Hemisphere, as is well known, is very high. The following findings are obtained: (1) There exist seasonal southward and northward movements in the position of the nonstationarity zones of the global stationary waves. The steady stationary waves occur in midlatitudes (35°-55°N) in winter and in the subtropical region (south of 35°N) in summer, associated with the major troughs over East Asia and North America and the weak European trough in winter, and with the relatively steady subtropical high system in summer. A high value center of Ius is at 35°N in spring and 50°N in summer, which might be caused by the seasonal variation of stationary-wave intensity, particularly in association with the interannual variability of trough ridge positions of stationary waves on the monthly mean maps. (2) There exists obvious asymmetry in Ilus, with the steady zones always located in the areas controlled by strong troughs/ridges and the unsteady ones in the areas where the stationary-wave intensity is low. The Ilus in the subtropics (south of 35°N) is larger in winter than in summer, and vice versa in the midlatitude region (north of 35°N). The summertime distribution of Ilus on the whole shows a rather complicated structure. However, North Europe is the most unsteady area for local stationary waves, as represented by high values of Ilus in both summer and winter, while over the North American continent (about 120°E-60°W), the °Ilus is slightly less than 1 in summer, indicating that the stationary waves in this region are more steady than those over other mid and high latitude regions. (3) From North China to Northwest Pacific, there is a high value zone of Ilus in summer, with its center (45°N, 130°E) located in the east of Heilongjiang Province. This influences the summer climate of northern China, including Northeast, North, and Northwest China. It is obvious that the nonstationarity is an intrinsic attribute of stationary waves, and can be regarded as being of the same importance as the intensity and energy-spectrum structure of stationary waves in the studies of the general circulation system. 相似文献
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15.
CLIMATE CHANGE: LONG-TERM TRENDS AND SHORT-TERM
OSCILLATIONS 总被引：2，自引：0，他引：2
Identifying the Northern Hemisphere (NH) temperature reconstruction and instrumental data for
the past 1000 years shows that climate change in the last millennium includes long-term trends and various
oscillations. Two long-term trends and the quasi-70-year oscillation were detected in the global temperature
series for the last 140 years and the NH millennium series. One important feature was emphasized that
temperature decreases slowly but it increases rapidly based on the analysis of different series. Benefits can be
obtained of climate change from understanding various long-term trends and oscillations. Millennial temperature
proxies from the natural climate system and time series of nonlinear model system are used in understanding the
natural climate change and recognizing potential benefits by using the method of wavelet transform analysis. The
results from numerical modeling show that major oscillations contained in numerical solutions on the
interdecadal timescale are consistent with that of natural proxies. It seems that these oscillations in the climate
change are not directly linked with the solar radiation as an external forcing. This investigation may conclude
that the climate variability at the interdecadal timescale strongly depends on the internal nonlinear effects in the climate system. 相似文献
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17.
B. G. Hunt 《Climate Dynamics》2006,27(7-8):677-694
The CSIRO Mark 2 coupled global climatic model has been used to generate a 10,000-year simulation for ‘present’ climatic conditions. The model output has been analysed to identify sustained climatic fluctuations, such as those attributed to the Medieval Warm Period (MWP) and the Little Ice Age (LIA). Since no external forcing was permitted during the model run all such fluctuations are attributed to naturally occurring climatic variability associated with the nonlinear processes inherent in the climatic system. Comparison of simulated climatic time series for different geographical locations highlighted the lack of synchronicity between these series. The model was found to be able to simulate climatic extremes for selected observations for century timescales, as well as identifying the associated spatial characteristics. Other examples of time series simulated by the model for the USA and eastern Russia had similar characteristics to those attributed to the MWP and the LIA, but smaller amplitudes, and clearly defined spatial patterns. A search for the frequency of occurrence of specified surface temperature anomalies, defined via duration and mean value, revealed that these were primarily confined to polar regions and northern latitudes of Europe, Asia and North America. Over the majority of the oceans and southern hemisphere such climatic fluctuations could not be sustained, for reasons explained in the paper. Similarly, sustained sea–ice anomalies were mainly confined to the northern hemisphere. An examination of mechanisms associated with the sustained climatic fluctuations failed to identify a role for the North Atlantic Oscillation, the El Niño-Southern Oscillation or the Pacific Decadal Oscillation. It was therefore concluded that these fluctuations were generated by stochastic processes intrinsic to the nonlinear climatic system. While a number of characteristics of the MWP and the LIA could have been partially caused by natural processes within the climatic system, the inability of the model to reproduce the observed hemispheric mean temperature anomalies associated with these events indicates that external forcing must have been involved. Essentially the unforced climatic system is unable to sustain the generation of long-term climatic anomalies. 相似文献
18.
Michael E. Mann 《Climatic change》2011,107(3-4):267-276
Long Range Dependence (LRD) scaling behavior has been argued to characterize long-term surface temperature time series. LRD is typically measured by the so-called “Hurst” coefficient, “H”. Using synthetic temperature time series generated by a simple climate model with known physics, I demonstrate that the values of H obtained for observational temperature time series can be understood in terms of the linear response to past estimated natural and anthropogenic external radiative forcing combined with the effects of random white noise weather forcing. The precise value of H is seen to depend on the particular noise realization. The overall distribution obtained over an ensemble of noise realizations is seen to be a function of the relative amplitude of external forcing and internal stochastic variability and additionally in climate “proxy” records, the amount of non-climatic noise present. There is no obvious reason to appeal to more exotic physics for an explanation of the apparent scaling behavior in observed temperature data. 相似文献
19.
利用慢特征分析法提取二维非平稳系统中的外强迫特征 总被引：1，自引：1，他引：0
慢特征分析法（Slow Feature Analysis,SFA）是一个从快变的信号中提取慢变特征的有效方法,它的提出丰富了人们对非平稳系统外强迫特征的重建手段。本文以Henon映射为基础,构造二维非平稳系统模型,尝试SFA方法在二维复杂非平稳系统中重建外强迫特征的能力。试验表明,SFA方法能够较好地从单时变参数Henon映射中提取出外强迫信号;通过结合小波变换技术,可以还原双时变参数Henon映射中的外强迫信号。另外,本文利用SFA方法重建了北京市气温的外强迫信号,分析其外强迫信号的尺度特征及其可能的物理机制。这些工作将为气候系统驱动力的研究提供新的思路。 相似文献
20.
利用地面水平能见度估算并分析中国地区气溶胶光学厚度长期变化特征 总被引：7，自引：1，他引：6
首先对1980年前后能见度资料非均一性进行了处理, 得到中国地区1960～2005年能见度时间序列, 并由此估算得到气溶胶光学厚度时间序列。对比已有观测及研究结果, 本文获得的气溶胶光学厚度时间序列能够较好地反映出中国地区气溶胶光学厚度长期变化特征。中国地区气溶胶光学厚度呈现逐年增加的趋势, 但1985年后增加趋势减缓, 这种变化在大城市区域表现得更为明显。中国地区气溶胶光学厚度空间分布上呈现东南部高、 西北部低的特征, 东南部地区气溶胶光学厚度普遍大于0.4, 最大值出现在四川盆地, 气溶胶光学厚度超过0.8。 相似文献