Predictability of El Niño over the past 148 years

Forecasts of El Ni?o climate events are routinely provided and distributed, but the limits of El Ni?o predictability are still the subject of debate. Some recent studies suggest that the predictability is largely limited by the effects of high-frequency atmospheric 'noise', whereas others emphasize limitations arising from the growth of initial errors in model simulations. Here we present retrospective forecasts of the interannual climate fluctuations in the tropical Pacific Ocean for the period 1857 to 2003, using a coupled ocean-atmosphere model. The model successfully predicts all prominent El Ni?o events within this period at lead times of up to two years. Our analysis suggests that the evolution of El Ni?o is controlled to a larger degree by self-sustaining internal dynamics than by stochastic forcing. Model-based prediction of El Ni?o therefore depends more on the initial conditions than on unpredictable atmospheric noise. We conclude that throughout the past century, El Ni?o has been more predictable than previously envisaged.     

Coupled ocean-atmosphere dynamics in the Indian Ocean during 1997-98

Climate variability in the Indian Ocean region seems to be, in some aspects, independent of forcing by external phenomena such as the El Ni?o/Southern Oscillation. But the extent to which, and how, internal coupled ocean-atmosphere dynamics determine the state of the Indian Ocean system have not been resolved. Here we present a detailed analysis of the strong seasonal anomalies in sea surface temperatures, sea surface heights, precipitation and winds that occurred in the Indian Ocean region in 1997-98, and compare the results with the record of Indian Ocean climate variability over the past 40 years. We conclude that the 1997-98 anomalies--in spite of the coincidence with the strong El Ni?o/Southern Oscillation event--may primarily be an expression of internal dynamics, rather than a direct response to external influences. We propose a mechanism of ocean-atmosphere interaction governing the 1997-98 event that may represent a characteristic internal mode of the Indian Ocean climate system. In the Pacific Ocean, the identification of such a mode has led to successful predictions of El Ni?o; if the proposed Indian Ocean internal mode proves to be robust, there may be a similar potential for predictability of climate in the Indian Ocean region.     

A new approach to studying ENSO predictability： Conditional nonlinear optimal perturbation

A new approach, the conditional nonlinear optimal perturbation (CNOP) is introduced to study the predictability of El Nifio-Southern Oscillation (ENSO) using a theoretical coupled ocean-atmosphere model. The differences between CNOP and linear singular vector (LSV) are demonstrated. The results suggest that the nonlinear model and CNOP are superior in determining error growth for studying predictability of the ENSO. In particular, the CNOP approach is used to explore the nature of the ‘spring predictability barrier‘ in ENSO prediction.     

环流异常相似性演变的动力学机制

本文首先利用多年观测资料对月平均环流异常的相似性演变进行了分析。结果表明,环流异常演变过程中普遍存在着半年左右的相似韵律现象。进一步从理论上研究了相似韵律现象产生的动力学机制。最后用一个海气耦合模式进行了数值模拟和各种敏感性实验,结果不仅证实了理论分析的结果,也为进一步建立一个相似一动力模式提供了理论依据。     

Seasonal characteristics of the Indian Ocean Dipole during the Holocene epoch

The Indian Ocean Dipole (IOD)--an oscillatory mode of coupled ocean-atmosphere variability--causes climatic extremes and socio-economic hardship throughout the tropical Indian Ocean region. There is much debate about how the IOD interacts with the El Ni?o/Southern Oscillation (ENSO) and the Asian monsoon, and recent changes in the historic ENSO-monsoon relationship raise the possibility that the properties of the IOD may also be evolving. Improving our understanding of IOD events and their climatic impacts thus requires the development of records defining IOD activity in different climatic settings, including prehistoric times when ENSO and the Asian monsoon behaved differently from the present day. Here we use coral geochemical records from the equatorial eastern Indian Ocean to reconstruct surface-ocean cooling and drought during individual IOD events over the past approximately 6,500 years. We find that IOD events during the middle Holocene were characterized by a longer duration of strong surface ocean cooling, together with droughts that peaked later than those expected by El Ni?o forcing alone. Climate model simulations suggest that this enhanced cooling and drying was the result of strong cross-equatorial winds driven by the strengthened Asian monsoon of the middle Holocene. These IOD-monsoon connections imply that the socioeconomic impacts of projected future changes in Asian monsoon strength may extend throughout Australasia.     

Pt/Ni双层金属膜修饰n~+/n-Si电极的研究

用Pt、Ni或Pt/Ni金属膜修饰n~+/n-Si半导体表面后作为光阳极,在Fe(CN)_6~3-/4-溶液中组成光电化学电池,在最佳操作条件和65mW/cm~2光强时转换效率为7.4％。研究了金属膜的厚度对电池性能的影响。对半导体电极表面进行了X-光电子能谱分析。     

找K个最小生成树的并行算法

基于SIMD 机器——一种可以同时读但不可同时写的共享计算模型(CREW-PRAM)给出了找K 个最小生成树的并行算法,此算法需O(log~2n+Klogn~*)时间及O(n~2)处理器;而基于可以同时读、写的更强计算模型(CRCW-PRAM),求K 个最小生成树仅需O(Klogn)时间及O(n~2)处理器,这里n 是图的顶点数.     

A variational iteration method for studying the ENSO mechanism

A coupled system of the El Ni(n)o/La Ni(n)o-Southern Oscillation (ENSO) mechanism is studied. Using the variational iteration theory, the approximations of the solution of an ENSO model is obtained.     

Hankel矩阵和Vandermonde矩阵之逆的新矩阵表示式及快速算法

利用线性方程组是否有解给出Hankel矩阵、Vandermonde矩阵可逆的条件及求逆的递推公式，并给出了逆矩阵新的表示式．表明Hankel矩阵、Vandermonde矩阵的逆矩阵可以表示为一些特殊矩阵的乘积之和，并以Hankel矩阵为例，得到了求逆的快速算法，所需计算量为O(n^2)，一般n阶矩阵求逆的计算量为O(n^2)．     

Proxy evidence for an El Niño-like response to volcanic forcing

Past studies have suggested a statistical connection between explosive volcanic eruptions and subsequent El Ni?o climate events. This connection, however, has remained controversial. Here we present support for a response of the El Ni?o/Southern Oscillation (ENSO) phenomenon to forcing from explosive volcanism by using two different palaeoclimate reconstructions of El Ni?o activity and two independent, proxy-based chronologies of explosive volcanic activity from ad 1649 to the present. We demonstrate a significant, multi-year, El Ni?o-like response to explosive tropical volcanic forcing over the past several centuries. The results imply roughly a doubling of the probability of an El Ni?o event occurring in the winter following a volcanic eruption. Our empirical findings shed light on how the tropical Pacific ocean-atmosphere system may respond to exogenous (both natural and anthropogenic) radiative forcing.     

_n型仿射Weyl群a值5的A_2×A_(12)×A_(11)型左胞腔

描述了_n型仿射Weyl群a值为5的A_2×A_(12)×A_(11)型左胞腔的个数.通过计算得到:当n=7时,这样的左胞腔个数为32;当n≥8时,左胞腔个数为1/12(n~4-2n~3-55n~2+224n-204).     

Interannual atmospheric variability forced by the deep equatorial Atlantic Ocean

Climate variability in the tropical Atlantic Ocean is determined by large-scale ocean-atmosphere interactions, which particularly affect deep atmospheric convection over the ocean and surrounding continents. Apart from influences from the Pacific El Ni?o/Southern Oscillation and the North Atlantic Oscillation, the tropical Atlantic variability is thought to be dominated by two distinct ocean-atmosphere coupled modes of variability that are characterized by meridional and zonal sea-surface-temperature gradients and are mainly active on decadal and interannual timescales, respectively. Here we report evidence that the intrinsic ocean dynamics of the deep equatorial Atlantic can also affect sea surface temperature, wind and rainfall in the tropical Atlantic region and constitutes a 4.5-yr climate cycle. Specifically, vertically alternating deep zonal jets of short vertical wavelength with a period of about 4.5?yr and amplitudes of more than 10?cm?s(-1) are observed, in the deep Atlantic, to propagate their energy upwards, towards the surface. They are linked, at the sea surface, to equatorial zonal current anomalies and eastern Atlantic temperature anomalies that have amplitudes of about 6?cm?s(-1) and 0.4?°C, respectively, and are associated with distinct wind and rainfall patterns. Although deep jets are also observed in the Pacific and Indian oceans, only the Atlantic deep jets seem to oscillate on interannual timescales. Our knowledge of the persistence and regularity of these jets is limited by the availability of high-quality data. Despite this caveat, the oscillatory behaviour can still be used to improve predictions of sea surface temperature in the tropical Atlantic. Deep-jet generation and upward energy transmission through the Equatorial Undercurrent warrant further theoretical study.     

短期区域气候预测系统及回报试验

为了提高短期区域气候预测准确率,针对我国大陆区域及周边海域,通过国家气候中心全球海气耦合模式嵌套一个区域大气-海洋耦合模式,建立了一套短期区域气候预测系统。利用该预测系统对2006-2011年逐年7月的气候特征进行了回报试验,对比分析了区域模式相对于全球模式预测高空形势场的差异,评估了预测系统对地面温度和降水的预测能力。试验表明:同化后,初估场质量显著提高;区域模式在预测高空形势场方面优于全球模式;相对于单独的大气模式,海气耦合模式在预测中低空的温度和湿度方面有一定的改善;系统对地面气温和降水均具有一定的预报能力,其中降水预测稍好。     

关于n~2+C型素数无穷多性的证明

本文利用“素数的表示法定理”和同余、二次剩余的性质,证明了 n~2+C 型素数的个数π_1(X_1)与π(X)关系的一个近似公式。     

数集构成4n阶泛对角线幻方的充分条件

本文以构造性方法证明:当8×2n~2型偏差分对称矩阵满足适当条件时,其元素之集可构成4n(n≥1)阶泛对角线幻方。构成二维等差矩阵的数集及由1,2,…,16n~2构成的数集仅是该种数集的特例。     

海洋大气和环境卫星遥感技术进展

 分别从海雾、海上强对流、海洋环境监测角度,介绍了卫星遥感监测能力、方法和相关产品的最新进展。卫星监测能力上,发展方向主要为高低轨、主被动协同观测;数据提取和产品反演方面,遥感反演算法趋于多样化且逐渐稳定成熟。基于卫星遥感对高层大气（以强对流为代表）、边界层大气（以海雾为代表）以及海洋环境（以海洋藻类、水体组分参数为代表）的评估,已经从科学研究过渡到业务监测,进一步提升了对海洋大气和生态环境的监测能力。     

大西洋热盐环流减弱对热带太平洋气候平均态及年际变率的影响

利用一个完全耦合的海气模式, 通过对比分析两组试验中海表温度、盐度、风应力等气候态变化特征以及ENSO强度和频率的变化, 研究热带太平洋气候平均态及年际变率对热盐环流减弱的响应。在北大西洋高纬地区注入1 Sv淡水后, 大西洋经向翻转流(AMOC)减弱约90%, 这直接导致向北的经向热量输送减少, 使北大西洋有明显降温, 南大西洋略有升温。这些变化会经过大气和海洋的远程传播以及局地海气反馈作用, 影响热带太平洋气候平均态: 赤道东西太平洋的SST都略有增温, 但纬向温度梯度和纬向风应力并没有太大变化, 赤道太平洋温跃层的深度和倾斜度也基本保持不变。相应地, ENSO强度和频率也没有明显变化。由此得出结论: 热盐环流减弱会引起全球气候平均态的变化, 但对热带太平洋的年际变率没有太大影响。     

Numerical simulation of the sensitivity of the Pacific subtropical-tropical meridional cell to global warming

Sensitivity of the Pacific subtropical-tropical meridional cell to global warming is examined by using a global ocean-atmosphere coupled model developed at LASG/IAP. Results indicate that associated with the increasing of atmospheric carbon dioxide, the most prominent signals of global warming locate at high latitudes, and the change of middle and low latitudes, in particular the surface wind, is relatively weak, which leads to a weak response of the Pacific subtropical-tropical meridional cell. At the time of atmospheric carbon dioxide doubling, the change of the meridional cell strength is smaller than the amplitude of natural variability.     

Impact of the closure of Indonesian seaway on climate: A numerical modeling study

Using a global OGCM and its relevant coupled ocean-atmosphere GCM with the contemporary, 6 MaBP and 14 MaBP oceanic topography, respectively, a series of numerical experiments are implemented in order to investigate the effect of the north shift of Australian continent on the tropical oceanic circulation, especially the formation of the western Pacific warm pool. The numerical experiments of the individual OGCM forced by the modern atmospheric circulation indicate that the closure of Indonesian passage results in warming in the tropical Pacific Ocean and cooling in the tropical Indian Ocean; furthermore, it also results in change in source of the Indonesian Through Flow (ITF) water, e.g. ITF mainly originates from the south Pacific at 14 MaBP, but it mainly originates from the north Pacific now. The coupled model shows similar results as the individual OGCM qualitatively.     

基于散列技术的快速子串归并算法

用统计方法研究东西方语言的多词单元问题和东方语言的未登录词问题时需要删除同频子串(子串归并)．传统的子串归并算法时间复杂度为O(n^2),在大规模语料库的处理中效率低下．提出一种基于散列技术的时间复杂度为O(n^2)的子串归并算法,并用数学方法证明其与O(n^2)复杂度的算法等价,即输入相同时输出也相同．不同规模语料上的实验结果表明新算法能够大大缩短子串归并所需时间,适用于大规模语料库的处理．