气候突变的子波分析   总被引：54，自引：3，他引：54       下载免费PDF全文

刘太中  荣平平  刘式达  郑祖光  刘式适 《地球物理学报》1995,38(2):158-162

对气候突变的研究，以往多采用统计方法．本文强调气候是多尺度、多层次的这一观点，并用子波变换方法分析了北半球平均温度资料，进一步证实了１９２０年为气候突变点．同时也找到了较低层次（１０１年尺度，１００年尺度）上的突变点的年代．分析结果较为客观并符合实际．  相似文献   

Structure and Dynamics of Katabatic Flow Jumps: Idealised Simulations     

Ye Yu  Xiao-Ming Cai 《Boundary-Layer Meteorology》2006,118(3):527-555

For the first time, results from a high-resolution numerical simulation (with horizontal grid spacing of 35m) were used to reveal the detailed structure near an atmospheric katabatic jump over an idealized slope. The simulation represents flow over the slopes of Coats Land, Antarctica for austral winter conditions. The katabatic jump is characterised by an updraft with vertical velocities of order 1ms⁻¹ and serves as a possible forcing mechanism for the gravity waves frequently observed over the ice shelves around the Antarctic. Results also indicate that strong turbulence is generally confined within a mixing zone near the top of the katabatic layer upstream of the jump and extends downstream through the top of the strong updraft associated with the jump. Detailed analyses of momentum and heat budgets across the katabatic jump indicate that, upstream of the jump, turbulent mixing is important in decelerating the upper part of the katabatic layer, while within the jump the upslope pressure gradient force associated with the pool of cold air plays a role in decelerating the flow near the surface. The heat budget near the jump reveals a simple two-term balance: the turbulent heat flux divergence is balanced by the advection. A comparison of model results with available theories indicates that mixing between layers of different potential temperature structure indeed plays some role in the development of katabatic flow jumps, especially for strong jumps. Theories used to study katabatic jumps should include this mixing process, of which the amount depends on the intensity of the jump. A conceptual model of a katabatic jump, including the main dynamical processes, is constructed from these detailed analyses.  相似文献   

Atmospheric Circulation Characteristics Associated with the Onset of Asian Summer Monsoon   总被引：1，自引：0，他引：1  

李崇银  潘静 《大气科学进展》2006,23(6):925-939

The onset of the Asian summer monsoon has been a focus in the monsoon study for many years. In this paper, we study the variability and predictability of the Asian summer monsoon onset and demonstrate that this onset is associated with specific atmospheric circulation characteristics. The outbreak of the Asian summer monsoon is found to occur first over the southwestern part of the South China Sea (SCS) and the Malay Peninsula region, and the monsoon onset is closely related to intra-seasonal oscillations in the lower atmosphere. These intra-seasonal oscillations consist of two low-frequency vortex pairs, one located to the east of the Philippines and the other over the tropical eastern Indian Ocean. Prior to the Asian summer monsoon onset, a strong low-frequency westerly emerges over the equatorial Indian Ocean and the low-frequency vortex pair develops symmetrically along the equator. The formation and evolution of these low-frequency vortices are important and serve as a good indicator for the Asian summer monsoon onset. The relationship between the northward jumps of the westerly jet over East Asia and the Asian summer monsoon onset over SCS is investigated. It is shown that the northward jump of the westerly jet occurs twice during the transition from winter to summer and these jumps are closely related to the summer monsoon development. The first northward jump (from 25–28N to around 30N) occurs on 8 May on average, about 7 days ahead of the summer monsoon onset over the SCS. It is found that the reverse of meridional temperature gradient in the upper-middle troposphere (500–200 hPa) and the enhancement and northward movement of the subtropical jet in the Southern Hemispheric subtropics are responsible for the first northward jump of the westerly jet.  相似文献   

Bayesian Mixture Modelling in Geochronology via Markov Chain Monte Carlo     

Ajay Jasra  David A. Stephens  Kerry Gallagher  Christopher C. Holmes 《Mathematical Geology》2006,38(3):269-300

In this paper we develop a generalized statistical methodology for characterizing geochronological data, represented by a distribution of single mineral ages. The main characteristics of such data are the heterogeneity and error associated with its collection. The former property means that mixture models are often appropriate for their analysis, in order to identify discrete age components in the overall distribution. We demonstrate that current methods (e.g., Sambridge and Compston, 1994) for analyzing such problems are not always suitable due to the restriction of the class of component densities that may be fitted to the data. This is of importance, when modelling geochronological data, as it is often the case that skewed and heavy tailed distributions will fit the data well. We concentrate on developing (Bayesian) mixture models with flexibility in the class of component densities, using Markov chain Monte Carlo (MCMC) methods to fit the models. Our method allows us to use any component density to fit the data, as well as returning a probability distribution for the number of components. Furthermore, rather than dealing with the observed ages, as in previous approaches, we make the inferences of components from the “true” ages, i.e., the ages had we been able to observe them without measurement error. We demonstrate our approach on two data sets: uranium-lead (U-Pb) zircon ages from the Khorat basin of northern Thailand and the Carrickalinga Head formation of southern Australia.  相似文献   

Markov Chain Monte Carlo Implementation of Rock Fracture Modelling   总被引：1，自引：0，他引：1  

K. V. Mardia  V. B. Nyirongo  A. N. Walder  C. Xu  P. A. Dowd  R. J. Fowell  J. T. Kent 《Mathematical Geology》2007,39(4):355-381

This paper deals with the problem of estimating fracture planes, given only the data at borehole intersections with fractures. We formulate an appropriate model for the problem and give a solution to fitting the planes using a Markov chain Monte Carlo (MCMC) implementation. The basics of MCMC are presented, with particular emphasis given to reversible jump, which is required for changing dimensions. We also give a detailed worked example of the MCMC implementation with reversible jump since our implementation relies heavily on this new methodology. The methods are tested on both simulated and real data. The latter is a unique data set in the form of a granite block, which was sectioned into slices. All joints were located and recorded, and the joint planes obtained by stacking strike lines. This work is important in the risk assessment for the underground storage of hazardous waste. Problems and extensions are discussed.  相似文献   

Quantification of longitudinal dispersion by upscaling Brownian motion of tracer displacement in a 3D pore-scale network model     

R.C. Acharya  M.I.J. van Dijke  K.S. Sorbie  S.E.A.T.M. Van der Zee  A. Leijnse 《Advances in water resources》2007

We present a 3D network model with particle tracking to upscale 3D Brownian motion of non-reactive tracer particles subjected to a velocity field in the network bonds, representing both local diffusion and convection. At the intersections of the bonds (nodes) various jump conditions are implemented. Within the bonds, two different velocity profiles are used. At the network scale the longitudinal dispersion of the particles is quantified through the coefficient D_L, for which we evaluate a number of methods already known in the literature. Additionally, we introduce a new method for derivation of D_L based on the first-arrival times distribution (FTD). To validate our particle tracking method, we simulate Taylor’s classical experiments in a single tube. Subsequently, we carry out network simulations for a wide range of the characteristic Péclet number Pe_? to assess the various methods for obtaining D_L. Using the new method, additional simulations have been carried out to evaluate the choice of nodal jump conditions and velocity profile, in combination with varying network heterogeneity. In general, we conclude that the presented network model with particle tracking is a robust tool to obtain the macroscopic longitudinal dispersion coefficient. The new method to determine D_L from the FTD statistics works for the full range of Pe_?, provided that for large Pe_? a sufficiently large number of particles is used. Nodal jump conditions should include molecular diffusion and allow jumps in the upstream direction, and a parabolic velocity profile in the tubes must be implemented. Then, good agreement with experimental evidence is found for the full range of Pe_?, including increased D_L for increased porous medium heterogeneity.  相似文献   

自动站分钟数据跳变对日极值影响的处理方法     

汪可可  胡容  吕素珍  张好艳  王国安 《河南气象》2007,(Z1)

自动站分钟数据常出现跳变现象,对跳变数据,首先应分析是否为野值。其次再判断野值是否影响日极值。然后分析日极值是否出现在该时次内,若不出现在该时次,极值从其他正常时次中挑取;若出现在该时次,应从自动站实有记录和人工观测或自记纸中挑取,若用人工记录代替,极值出现时间为缺测。  相似文献   

Interdecadal Change of the Northward Jump Time of the Western Pacific Subtropical High in Association with the Pacific Decadal Oscillation          下载免费PDF全文

YE Tianshu  SHEN Qian  WANG Kuo  ZHANG Zhisen  ZHAO Junhu 《Acta Meteorologica Sinica》2015,29(1):59-71

In this paper, the northward jump time of the western Pacific subtropical high(WPSH) is defined and analyzed on the interdecadal timescale. The results show that under global warming, significant interdecadal changes have occurred in the time of the WPSH northward jumps. From 1951 to 2012, the time of the first northward jump of WPSH has changed from "continuously early" to "continuously late", with the transition occurring in 1980. The time of the second northward jump of WPSH shows a similar change, with the transition occurring in 1978. In this study, we offer a new perspective by using the time of the northward jump of WPSH to explain the eastern China summer rainfall pattern change from "north-abundant-southbelow-average" to "south-abundant-north-below-average" at the end of the 1970 s. The interdecadal change in the time of the northward jump of WPSH corresponds not only with the summer rainfall pattern, but also with the Pacific decadal oscillation(PDO). The WPSH northward jump time corresponding to the cold(warm) phase of the PDO is early(late). Although the PDO and the El Nino–Southern Oscillation(ENSO)both greatly influence the time of the two northward jumps of WPSH, the PDO’s effect is noticed before the ENSO’s by approximately 1–2 months. After excluding the ENSO influence, we derive composite vertical atmospheric circulation for different phases of the PDO. The results show that during the cold(warm)phase of the PDO, the atmospheric circulations at 200, 500, and 850 h Pa all contribute to an earlier(later)northward jump of the WPSH.  相似文献   

1961-2014年黄河源区蒸发皿蒸发量变化的多尺度特征及突变分析     

石明星  蓝永超  沈永平  田辉  王欣  喇承芳  马虎迎 《冰川冻土》2018,40(4):666-675

基于黄河源区相关气象站1961-2014年蒸发皿蒸发数据,利用线性倾向分析、滑动平均法、Mann-Kendall法等方法,对黄河源区各分区及整个源区蒸发皿蒸发量变化进行多尺度变化特征及突变分析。结果表明：近50余年来,空间上,黄河源区年平均蒸发量经历了从上游到下游先减小后增加的过程,季节蒸发量变化稍有差异;时间上,黄河源区季节及年平均蒸发量总体呈上升趋势,各分区略有差异,各分区及整个源区蒸发量年代际变化具有较好的一致性。各分区及整个黄河源区年平均及季节平均蒸发量突变点基本一致,均出现在2000年前后,且年与季节平均蒸发量在突变前均值大部分小于突变后的均值。位于源区下游的玛曲-兴海平均蒸发量发生突变的时间较早,且跳跃幅度较小,位于源区中游的达日-玛曲平均蒸发量发生突变的时间较晚,且跳跃幅度较大。对各气象因子的相关分析表明,影响源区年蒸发量变化的主要因子为平均温度。  相似文献   

利用中位数的GPS卫星钟跳探测方法   总被引：2，自引：0，他引：2  

吴静 《测绘科学》2015,40(6):36-41

GPS卫星钟跳是导航卫星钟差数据处理中的一种常见的数据异常。针对由钟差数据量较大引起的粗差探测效率低下,影响用户定位精度的问题,该文对基于中位数的粗差探测方法进行研究;并在分析钟差数据特性的基础上将此方法进行扩展,使其不仅能够探测卫星钟差数据中的粗差,还能探测卫星钟跳。实验结果表明,该文方法能够较好地进行粗差探测和钟跳探测。  相似文献