不同趋势对滑动移除近似熵的影响

许多观测资料中存在着各种各样的趋势,如季节变化引起的周期性趋势、全球变暖所造成的线性趋势、多项式趋势等.鉴于此,本文研究了各种趋势对滑动移除近似熵的影响.数值试验结果表明,周期性趋势、线性趋势及非线性趋势均对滑动移除近似熵的突变检测结果影响较小,论证了滑动移除近似熵方法检测突变的可靠性,为该方法在实际观测资料中的广泛应用提供了实验基础.     

旱涝预测的演化建模方法

发展了一种旱涝预测的演化建模方法, 数值试验结果表明, 该方法能够从历史资料中准确地挖掘出气候要素演化的主要动力学特征, 所建立的模型不仅能够较好地模拟要素的历史演变情况, 而且还能够对未来的演变趋势进行准确的预测. 对于演化建模所得到的误差较大的模型, 对其预测误差序列进行二次演化建模可明显提高模型的预测精度.     

求解对流扩散方程的四种差分格式的比较

利用对流扩散方程，在边界和参数存在随机扰动的情况下，考察四种差分格式的优劣，为求 解对流扩散方程提供一种可靠的差分格式，并得到通过空间加密网格的方法可以控制边界、 参数随机影响的结论. 关键词： 对流扩散方程 差分格式 随机扰动     

Collective behaviour of climate indices in the North Pacific airben sea system and its potential relationships with decadal climate changes

A climate network of six climate indices of the North Pacific air-sea system is constructed during the period of 1948-2009. In order to find out the inherent relationship between the intrinsic mechanism of climate index network and the important climate shift, the synchronization behaviour and the coupling behaviour of these indices are investigated. Results indicate that climate network synchronization happened around the beginning of the 1960s, in the middle of the 1970s and at the beginnings of the 1990s and the 2000s separately. These synchronization states were always followed by the decrease of the coupling coefficient. Each synchronization of the network was well associated with the abrupt phase or trend changes of annually accumulated abnormal values of North Pacific sea-surface temperature and 500-hPa height, among which the one that happened in the middle of the 1970s is the most noticeable climate shift. We can also obtain this mysterious shift from the first mode of the empirical orthogonal function of six indices. That is to say, abrupt climate shift in North Pacific air-sea system is not only shown by the phase or trend changes of climate indices, but also might be indicated by the synchronizing and the coupling of climate indices. Furthermore, at the turning point of 1975, there are also abrupt correlation changes in the yearly mode of spatial degree distribution of the sea surface temperature and 500-hPa height in the region of the North Pacific, which further proves the probability of climate index synchronization and coupling shift in air-sea systems.     

基于EMD方法的非线性/非平稳时间序列的气候预测研究

目前，大多数统计预测模型均假设时间序列或观测数据是线性和平稳的。然而，自然界的观测资料是非线性和非平稳的，通常很难用这些数学模型预测它们。本文针对这一问题提出了一个新的预测方案，即首先利用经验模态分解方法将非线性/非平稳时间序列平稳化，得到一系列本征模函数(IMF)；其次用均生函数模型预测各IMF分量；最后以所有IMF的预测值为新样本对源序列作最优子集回归模型的拟合及预测。结果表明每个IMF，尤其是特征IMF(即特征层次)比源序列有更高的可预测性。该方案为气候预测开辟了一条新的有效途径。     

全球变暖对中国极端暖月事件的潜在影响

利用极值理论（extreme value theory, EVT）中的广义帕雷托分布（generalized Pareto distribution, GPD）,结合空间参数估计方案研究了中国1960—2007年740站的月平均温度距平中极端暖月事件（extreme warm month events,EWME）的空间分布特征,给出了历史上典型EWME的重现时间估计,重点分析了区域气候变暖作为强迫因子对EWME分布的潜在影响.分析表明：1）中国EWME的性质的空间分布差异较大,青藏高原西部、中国西南地区、 关键词： 极端气候事件 帕雷托分布 全球变暖     

基于概率密度分布型变化的突变检测新途径

对于一个稳定的动力系统而言,系统变量的概率密度具有较为稳定的分布型,而当系统的动力学结构发生变化后可能会导致系统变量的分布型发生不同程度的变化.鉴于此,本文从识别系统变量的概率密度分布的微小变化角度出发,将描述时间序列概率分布特征的偏度系数和峰度系数应用于时间序列的突变检测中.数值试验结果表明,偏度系数和峰度系数对突变信号具有很好的识别能力,进而揭示了一条检测突变的新途径.进一步的研究表明,新方法的检测结果对于子序列长度的选择具有较小的依赖性.     

Spatiotemporal characteristics and water budget of water cycle elements in different seasons in northeast China

In this paper, we study the spatiotemporal characteristics of precipitable water, precipitation, evaporation, and water–vapor flux divergence in different seasons over northeast China and the water balance of that area. The data used in this paper is provided by the European Center for Medium-Range Weather Forecasts(ECMWF). The results show that the spatial distributions of precipitable water, precipitation, and evaporation feature that the values of elements above in the southeastern area are larger than those in the northwestern area; in summer, much precipitation and evaporation occur in the Changbai Mountain region as a strong moisture convergence region; in spring and autumn, moisture divergence dominates the northeast of China; in winter, the moisture divergence and convergence are weak in this area. From 1979 to 2010, the total precipitation of summer and autumn in northeast China decreased significantly; especially from 1999 to 2010, the summer precipitation always demonstrated negative anomaly. Additionally, other elements in different seasons changed in a truly imperceptible way. In spring, the evaporation exceeded the precipitation in northeast China; in summer, the precipitation was more prominent; in autumn and winter, precipitation played a more dominating role than the evaporation in the northern part of northeast China, while the evaporation exceeded the precipitation in the southern part.The Interim ECMWF Re-Analysis(ERA-Interim) data have properly described the water balance of different seasons in northeast China. Based on ERA-Interim data, the moisture sinks computed through moisture convergence and moisture local variation are quite consistent with those computed through precipitation and evaporation, which proves that ERAInterim data can be used in the research of water balance in northeast China. On a seasonal scale, the moisture convergence has a greater influence than the local moisture variation on a moisture sink, and the latter is variable slightly, generally as a constant. Likewise, in different seasons, the total precipitation has a much greater influence than the evaporation on the moisture sink.     

随机扰动对拟小波方法求解对流扩散方程的影响

引进拟小波方法数值求解对流扩散方程，研究结果表明，计算带宽W有一个极值，当计算带宽W取该极值时，该方程的拟小波解的精度最高，且好于迎风格式。当边界发生随机不等幅扰动时，对于积分时间较长的情况，拟小波格式的效果要稍逊于迎风格式；当边界发生随机等幅扰动时，若计算带宽W取大于等于20的整数时，方程拟小波解的精度与迎风格式相同；当参数受到随机扰动时，W取10时的拟小波解的均方根误差要小于迎风格式；在初值发生随机扰动且计算带宽W取10时，方程的拟小波解的精度最高，好于迎风格式。     

无反馈作用下混沌系统的振幅死亡

考虑了一种无反馈的作用机理，通过分析定常强迫作用下R?ssler系统的分岔图和Lyapunov指数谱，发现定常强迫能够导致混沌系统产生振幅死亡.这种现象的产生类似于耦合的极限环系统和耦合的R?ssler系统，弱定常强迫作用下的R?ssler系统经由一个周期运动被驱动到系统自身的一个平衡点上.进一步对受迫系统时间序列的研究表明，当定常强迫强度超过一个临界值时，系统的状态不断在小振幅周期运动与静止之间交替出现. 关键词： 振幅死亡 定常强迫 R?ssler系统