Evolution-induced catastrophe and its predictability

Both earthquake prediction and failure prediction of disordered brittle media are difficult and complicated problems and they might have something in common. In order to search for clues for earthquake prediction, the common features of failure in a simple nonlinear dynamical model resembling disordered brittle media are examined. It is found that the failure manifests evolution-induced catastrophe (EIC), i.e., the abrupt transition from globally stable (GS) accumulation of damage to catastrophic failure. A distinct feature is the significant uncertainty of catastrophe, called sample-specificity. Consequently, it is impossible to make a deterministic prediction macroscopically. This is similar to the question of predictability of earthquakes. However, our model shows that strong stress fluctuations may be an immediate precursor of catastrophic failure statistically. This might provide clues for earthquake forecasting.

The degree of predictability of earthquakes in several regions of China: statistical analysis of historical data

The stress release model, a stochastic version of the elastic-rebound theory, is applied to the historical earthquake data from three strong earthquake-prone regions of China, including North China, Southwest China, and the Taiwan seismic regions. The results show that the seismicity along a plate boundary (Taiwan) is more active than in intraplate regions (North and Southwest China). The degree of predictability or regularity of seismic events in these seismic regions, based on both the Akaike information criterion (AIC) and fitted sensitivity parameters, follows the order Taiwan, Southwest China, and North China, which is further identified by numerical simulations. (c) 2004 Elsevier Ltd. All rights reserved.

Dynamics of nonlinear error growth and season-dependent predictability of El Nino events in the Zebiak-Cane model

With the intermediate-complexity Zebiak-Cane model, we investigate the 'spring predictability barrier' (SPB) problem for El Nino events by tracing the evolution of conditional nonlinear optimal perturbation (CNOP), where CNOP is superimposed on the El Nino events and acts as the initial error with the biggest negative effect on the El Nino prediction. We show that the evolution of CNOP-type errors has obvious seasonal dependence and yields a significant SPB, with the most severe occurring in predictions made before the boreal spring in the growth phase of El Nino. The CNOP-type errors can be classified into two types: one possessing a sea-surface-temperature anomaly pattern with negative anomalies in the equatorial central-western Pacific, positive anomalies in the equatorial eastern Pacific, and a thermocline depth anomaly pattern with positive anomalies along the Equator, and another with patterns almost opposite to those of the former type. In predictions through the spring in the growth phase of El Nino, the initial error with the worst effect on the prediction tends to be the latter type of CNOP error, whereas in predictions through the spring in the decaying phase, the initial error with the biggest negative effect on the prediction is inclined to be the former type of CNOP error. Although the linear singular vector (LSV)-type errors also have patterns similar to the CNOP-type errors, they cover a more localized area than the CNOP-type errors and cause a much smaller prediction error, yielding a less significant SPB. Random errors in the initial conditions are also superimposed on El Nino events to investigate the SPB. We find that, whenever the predictions start, the random errors neither exhibit an obvious season-dependent evolution nor yield a large prediction error, and thus may not be responsible for the SPB phenomenon for El Nino events. These results suggest that the occurrence of the SPB is closely related to particular initial error patterns. The two kinds of CNOP-type error are most likely to cause a significant SPB. They have opposite signs and, consequently, opposite growth behaviours, a result which may demonstrate two dynamical mechanisms of error growth related to SPB: in one case, the errors grow in a manner similar to El Nino; in the other, the errors develop with a tendency opposite to El Nino. The two types of CNOP error may be most likely to provide the information regarding the 'sensitive area' of El Nino-Southern Oscillation (ENSO) predictions. If these types of initial error exist in realistic ENSO predictions and if a target method or a data assimilation approach can filter them, the ENSO forecast skill may be improved. Copyright (C) 2009 Royal Meteorological Society

Equatorial pacific SSTA-related decadal variations of potential predictability of ENSO and interannual climate

Based on analysis of NCEP reanalysis data and SST indices of the recent 50 years, decadal changes of the potential predictability of ENSO and interannual climate anomalies were investigated. Autocorrelation of Nino3 SST anomalies (SSTA) and correlation between atmospheric anomalies fields and Nino3 SSTA exhibit obvious variation in different decades, which indicates that Nino3 SSTA-related potential predictability of ENSO and interannual climate anomalies has significant decadal changes. Time around 1977 is not only a shift point of climate on the interdecadal time scale but also a catastrophe point of potential predictability of ENSO and interannual climate. As a whole, ENSO and the PNA pattern in boreal winter are more predictable in 1980s than in 1960s and 1970s, while the Nino3 SSTA-related potential predictability of the Indian monsoon and the East Asian Monsoon is lower in 1980s than in 1960s and 1970s.

Effects of Subgrid-Scale Modeling on Time Correlations in Large Eddy Simulation

The effects of the unresolved subgrid-scale (SGS) motions on the energy balance of the resolved scales in large eddy simulation (LES) have been investigated actively because modeling the energy transfer between the resolved and unresolved scales is crucial to constructing accurate SGS models. But the subgrid scales not only modify the energy balance, they also contribute to temporal decorrelation of the resolved scales. The importance of this effect in applications including the predictability problem and the evaluation of sound radiation by turbulent flows motivates the present study of the effect of SGS modeling on turbulent time correlations. This paper compares the two-point, two-time Eulerian velocity correlation in isotropic homogeneous turbulence evaluated by direct numerical simulation (DNS) with the correlations evaluated by LES using a standard spectral eddy viscosity. It proves convenient to express the two-point correlations in terms of spatial Fourier decomposition of the velocity field. The LES fields are more coherent than the DNS fields: their time correlations decay more slowly at all resolved scales of motion and both their integral scales and microscales are larger than those of the DNS field. Filtering alone is not responsible for this effect: in the Fourier representation, the time correlations of the filtered DNS field are identical to those of the DNS field itself. The possibility of modeling the decorrelating effects of the unresolved scales of motion by including a random force in the model is briefly discussed. The results could have applications to the problem of computing sound sources in isotropic homogeneous turbulence by LES

Statistical analysis of synthetic earthquake catalogs generated by models with various levels of fault zone disorder

The stress release model, a stochastic version of the elastic rebound theory, is applied to the large events from four synthetic earthquake catalogs generated by models with various levels of disorder in distribution of fault zone strength (Ben-Zion, 1996) They include models with uniform properties (U), a Parkfield-type asperity (A), fractal brittle properties (F), and multi-size-scale heterogeneities (M). The results show that the degree of regularity or predictability in the assumed fault properties, based on both the Akaike information criterion and simulations, follows the order U, F, A, and M, which is in good agreement with that obtained by pattern recognition techniques applied to the full set of synthetic data. Data simulated from the best fitting stress release models reproduce, both visually and in distributional terms, the main features of the original catalogs. The differences in character and the quality of prediction between the four cases are shown to be dependent on two main aspects: the parameter controlling the sensitivity to departures from the mean stress level and the frequency-magnitude distribution, which differs substantially between the four cases. In particular, it is shown that the predictability of the data is strongly affected by the form of frequency-magnitude distribution, being greatly reduced if a pure Gutenburg-Richter form is assumed to hold out to high magnitudes.

Subtropical dipole mode in the Southern Hemisphere: A global view

A global wavenumber-3 dipole SST mode is showed to exist in the Southern Hemisphere subtropical climate variability in austral summer. A positive (negative) phase of the mode is characterized by cool (warm) SST anomalies in the east and warm (cool) SST anomalies in the southwest of the south Indian, Pacific, and Atlantic Oceans, respectively. This coherent dipole structure is largely a response of ocean mixed layer to the atmospheric forcing characterized by migration and modulation of the subtropical high-pressures, in which the latent heat flux play a leading role through wind-induced evaporation, although ocean dynamics may also be crucial in forming SST anomalies attached to the continents. Exploratory analyses suggest that this mode is strongly damped by the negative heat flux feedback, with a persistence time about three months and no spectral peak at interannual to decadal time scales. As the subtropical dipole mode is linearly independent of ENSO and SAM, whether it represents an additional source of climate predictability should be further studied. Citation: Wang, F. (2010), Subtropical dipole mode in the Southern Hemisphere: A global view, Geophys. Res. Lett., 37, L10702, doi: 10.1029/2010GL042750.

Algorithm Studies on How to Obtain a Conditional Nonlinear Optimal Perturbation (CNOP)

The conditional nonlinear optimal perturbation (CNOP), which is a nonlinear generalization of the linear singular vector (LSV), is applied in important problems of atmospheric and oceanic sciences, including ENSO predictability, targeted observations, and ensemble forecast. In this study, we investigate the computational cost of obtaining the CNOP by several methods. Differences and similarities, in terms of the computational error and cost in obtaining the CNOP, are compared among the sequential quadratic programming (SQP) algorithm, the limited memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) algorithm, and the spectral projected gradients (SPG2) algorithm. A theoretical grassland ecosystem model and the classical Lorenz model are used as examples. Numerical results demonstrate that the computational error is acceptable with all three algorithms. The computational cost to obtain the CNOP is reduced by using the SQP algorithm. The experimental results also reveal that the L-BFGS algorithm is the most effective algorithm among the three optimization algorithms for obtaining the CNOP. The numerical results suggest a new approach and algorithm for obtaining the CNOP for a large-scale optimization problem.

热带海洋海温变率预报及可预报性研究

热带海洋是大尺度海气相互作用的关键区域，对全球气候变化有重要影响。厄尔尼诺与南方涛动（ENSO）及热带大西洋变率（TAV）是分别是热带太平洋、大西洋的最显著气候变率。对热带海洋海表温度（SST）的预报是预报ENSO和TAV的关键要素，对全球气候、生态环境及许多国家的防灾减灾、经济发展有非常重要的意义。 本文利用一个中等复杂程度的海－气耦合模式CCM3－RGO，对1980－2000年热带海洋SST变率进行回顾性预报。并创新性地在耦合模式中加入大气噪声过滤器，检验天气噪声等因素对预报的影响。 第一部分工作为ENSO预报。本文改进了初始化方案，并应用噪声过滤器减少天气噪声对耦合过程的影响，显著提高了ENSO预报技能，达到同类研究的先进水平。进一步分析表明，采用耦合同化方法产生的、与模式相容性和准确性皆优的初始条件，对2个季节以内的ENSO预报技巧的提高起主要作用；在适宜的初始条件下，过滤风应力中的天气噪声，可以增强海－气耦合过程的信噪比，改善模式对风－温跃层－SST相互作用的Bjerknes反馈机制的正确响应，对3－4季节预报技巧的改进起主要作用。 第二部分为热带大西洋SST预报。发现过滤热通量中的天气噪声可以加强局地热力学反馈，对以往预报水平较低的南热带大西洋SST预报有显著的改进作用。

工科大学生心理应激、应对与自我概念的关系研究

In the period of college, an individual matures rapidly in all aspects. College engineering students are the important parts of undergraduates. The state of an individual’s mental health may affect and even decide his future life and work. The level of the student’s self-concept and the kind of coping styles the students adopt are directly related to their mental health. So, it is significant to study the psychological stress, coping and self-concept of college engineering students for the mental health education and research of college engineering students. Based on overviews of former research, with the China College Student Psychological Stress Scale, the Coping Styles Scale and the Tennessee Self-Concept Scale, 559 college engineering students were investigated to explore the characteristics of and the relationship between the psychological stress, coping styles and self-concept of college engineering students. The results showed: 1. The stresses of learning, living and daily hassles were the main psychological stresses of college engineering students. There were significant differences in psychological stress between students from the countryside and those from urban areas, between needy students and non-needy students, between single-parent students and non-single-parent students, among students from different grades, with different academic achievements and of different postgraduate targets, between student party members and non-party members, between student cadres and non-cadres. However, there were no significant differences between male and female, between those from single-child families and from multiple-child families. 2. The coping styles of solving problem, seeking help and rationalization were the main coping styles of college engineering students. There were significant differences in the coping styles between needy students and non-needy students, among students from different grades, with different academic achievements and of different postgraduate targets, between student party members and non-party members, between student cadres and non-cadres. However, there were no significant differences between students from the countryside and from urban areas, between male and female, between single-parent students and non-single-parent students, between those from single-child families and from multiple-child families. 3. The self-concept of college engineering students was positive in general. There were significant differences in self-concept between students from the countryside and those from urban areas, between male and female, between needy students and non-needy students, between single-parent students and non-single-parent students, among students from different grades, with different academic achievements and of different postgraduate targets, between student party members and non-party members, between student cadres and non-cadres. However, there were no significant differences between those from single-child families and from multiple-child families. 4. The psychological stress had significantly negative correlation to the immature coping styles, and had partial correlation to the mature coping styles. Coping style has significant predictability on psychological stress. 5. The positive factors of the self-concept had significantly negative correlation to psychological stress, but self-criticism had positive correlation to psychological stress. There are significant differences between high self-concept students and low self-concept students for psychological stress. Self-concept has significant predictability on psychological stress. 6. The positive factors of the self-concept had significantly negative correlation to the coping styles of self-blame, illusion, avoidance, and rationalization, but had significantly positive correlation to the coping style of solving problem and seeking help. Self-criticism had significantly negative correlation to the coping styles of self-blame, illusion, avoidance, and rationalization. There are significant differences between high self-concept students and low self-concept students for coping styles. Self-concept has significant predictability on coping styles. 7. The self-concept of college engineering students had an effect on psychological stress by coping styles. However, the effect by the immature coping styles was higher than that to the mental health directly, and the effect by the mature and mixed coping styles was slighter than that to the mental health directly. According to the results, improving the college engineering students’ self-concept level and establishing right self-concept, developing the middle school student’ active coping styles and overcoming the negative coping styles are essential and important to the college engineering students’ mental health and provide useful clues for the psychological education of the college engineering students.