漏阈值系统的自组织临界性: 近平均场的动力学影响及其对地震、神经生物学和预测方面的意义

阈值系统被看作是自然界中某些最重要的非线性自组织系统,包括地震断层系统、神经网络、超导和半导体、互联网以及政治、社会和生态系统。所有这些系统都具有与时、空、强相关的动力学,且都典型地显示了时空尺度的多重性。我们在两种不同尺度上讨论地震阈值系统自组织的物理学问题：(1)“微观”的实验室尺度,来自模拟结果的考虑导致了动力学方程,这些方程可以推导从滑动实验中得到的结果;(2)“宏观”的地震断层系统尺度,强相关地震断层系统的物理学可以通过应用定义在希尔伯特本征态空间有关的态向量来理解。所有的这些系统中,长程相关导致局部各态历经动力学的存在。耗损效应的存在导致了“漏阈值”动力学的出现,它等同于一个控制与背景涨落尺度有关的成核事件尺度的新的标度场的出现。在宏观地震断层尺度的框架下,这些作为一种预报未来地震活动方法的观念显示出了比较大的希望。     

Fluvial geomorphology of the Middle Reach of the Huai River

The Middle Reach of the Huai River （MRHR） flows northeast into the Hongzehu Lake. Before entering the Hongzehu Lake, the Huai River has a braided channel which is shallow and wide, and the riverbed has a negative slope. Based on the characteristics of the MRHR, this river reach can be divided into the following sections： a quasi-straight （or mildly curved） section, a bend section, and a braided section. The majority of the MRHR is quasi-straight. In this paper, several parameters are used to assess the geomorphology of the MRHR. Statistical analyses are performed to establish a relationship between the span length ＂L＂ and channel width ＂B＂ for different channel patterns. The relationship between the meandering length ＂S＂ and bankfull channel width ＂B＂ is also derived. Results indicate that the bankfull channel width ＂B＂, the bankfull cross sectional area ＂A＂ and the average flow depth ＂H＂ are mainly dependent on the dominant discharge in the channel. A relationship is derived that describes the denendencv of the curvature radius ＂R＂ on the dominant discharae ＂O＂. water surface slone ＂J＂and the turning angle ＂α＂.     

An integrated suspended sediment transport monitoring and analysis concept

A new integrated suspended sediment monitoring strategy applying direct and indirect technologies is presented.Optical sensors continuously record the turbidity at one point in the channel cross section close to the river bank and are calibrated by water samples taken close to the sensor.Additionally measurements are performed to establish the distribution of suspended sediment in a cross section（bottle samples combined with acoustic devices）.Using correction factors（probe and cross-sectional factor） these monitoring methods are combined and it is,thus,possible to fully document the temporal and spatial variability of the suspended sediment transport and to estimate the suspended sediment load for certain time periods.This monitoring strategy was implemented at various measurement sites in Austria as well as at the Hainburg Road Bridge site on the Danube River.It has already been successfully applied for three years at this measurement site and suspended sediment loads during high discharges up to a 15 year flood event have been monitored.To evaluate the new monitoring methods the results were compared with load estimation methods found in the literature including averaging and ratio estimators as well as rating curves.The results prove that with the new methodology,the temporal variability of the suspended sediment transport can be detected more accurately compared with the other methods.They also demonstrate that the additional consideration of the spatial distribution of the suspended sediment concentration in the cross section is crucial as the mean concentration in the cross section can significantly exceed the concentration near the banks,especially at large rivers like the Danube River.     

近岸水体表层悬浮泥沙平均粒径遥感反演

悬浮泥沙的粒径分布特征不仅体现了悬浮颗粒态物质的存在状态,而且可以指示水动力及再悬浮作用的过程和强度,因此研究悬浮泥沙粒径分布特征具有重要意义。利用Mie理论建立悬浮泥沙平均粒径反演模型,结果表明,悬浮泥沙后向散射系数与其平均粒径的三次方线性关系明显,4个波段(412nm、443nm、555nm、667nm)拟合方程决定系数均在0.93以上,拟合误差最小值为16.6322%(412nm),最大值为20.3143%(667nm)。利用QAA算法从MODIS影像上反演研究区域悬浮泥沙后向散射系数,并结合反演的悬浮泥沙浓度推算研究区域表层悬浮泥沙的平均粒径。对比发现,近岸高悬浮泥沙区域的反演结果与实测数据吻合较好,相关研究可以为深入开展陆海相互作用、海洋生态系统演变和海洋参与全球碳循环等研究提供重要数据支持。     

沙漠绿洲过渡带典型下垫面风速脉动特征——以塔克拉玛干沙漠南缘策勒绿洲为例

以塔克拉玛干沙漠南缘策勒绿洲西部沙漠-绿洲过渡带为研究区,选择植被盖度 < 5%裸沙样地、植被盖度10%～15%柽柳样地和植被盖度20%～25%骆驼刺样地,利用可移动梯度风测量系统,获取了系统性天气过程中距离地表20 cm、40 cm、60 cm、100 cm和200 cm高度的风速及200 cm高度的风向系列数据,对3个样地平均风速、风速脉动和风向脉动进行分析和研究。结果表明:(1)植被的存在大幅度消弱了平均风速,随着植物密度的增加平均风速逐渐降低,风速廓线显示平均风速发生明显降低的转折高度与植被冠层的平均高度相对应。(2)3个样地脉动风速均近似服从高斯分布,可见植被的存在并未改变风速脉动分布规律。各样地风速脉动强度均随指示风速的增大而增大,随距离地表高度的降低而下降。风速脉动相对值总体上呈现随植物密度增大而增大的趋势,植物群落结构的差异增加了相对风速脉动垂直分布的复杂性。(3)风向脉动幅度以裸沙样地最小、柽柳样地次之、骆驼刺样地最大,即随植物密度增加而增大。同一样地内风向脉动值不随指示风速的变化而发生明显变化。     

新疆博斯腾湖流域风沙环境特征

通过风资料的统计和计算,对博斯腾湖流域风沙活动强度环境特征进行了系统的研究。结果表明:博斯腾湖流域年平均风速较小,一般1.6～3.0 m·s^-1;有效起沙风作用时间存在明显的区域差异,其中巴音布鲁克起沙风天数占全年总天数的55.59%,焉耆、轮台、巴音郭楞及和静分别为18.75%、12.72%、11.48%、11.23%,其余各站均低于10%;随着风速等级的增加,起沙风出现的频率相应减少,基本上都集中在6.1～10.0 m·s^-1;研究区方向变率指数(合成输沙势/输沙势,RDP/DP)0.49~0.68,属于中比率,风况特征属于纯双峰风况或锐双峰风况。输沙势属于低风能环境,且存在较大的区域差异。     

热带印度洋偶极子模态的不对称性及其成因的数值研究

热带印度洋偶极子 (Indian Ocean Dipole) 是印度洋海域内海洋和大气环流年际变化的主要特征模态之一, 在热带海气耦合系统中起到非常重要的作用。同热带太平洋的ENSO现象类似, 热带印度洋偶极子也呈现出显著的不对称性。本文利用中国科学院大气物理研究所发展的全球海洋环流模式, 在观测风应力距平的强迫下, 评估了模式对热带印度洋季节变化、 热带印度洋偶极子 (IOD) 模态及其不对称性的模拟能力, 并且通过数值试验分析了IOD模态不对称性特征及其对气候平均态的影响。对照观测资料, 模式较好地再现了热带印度洋SST在季风驱动下的季节变化特征。在年际时间尺度上, 模式不仅能够再现IOD指数的变化趋势, 而且可以成功模拟出IOD模态的空间分布特征, 即表层和次表层海温在西印度洋表现为正异常, 在东印度洋表现为负异常。可见, 对于热带印度洋而言, IOD模态主要是对风应力异常的响应。热带印度洋海温与Niño3.4指数的相关性分析表明, 模式能够模拟出超前热带太平洋ENSO现象2～4个月时海温的偶极子型分布, 但是不能模拟出滞后ENSO现象2个月左右的全海盆增暖模态, 可能是因为模式试验中没有考虑热通量年际异常的强迫。同时, 模式模拟的IOD模态具有同观测结果相类似的不对称性, 进一步的敏感性试验表明风应力的不对称性对偶极子指数的不对称性贡献较小, 次表层及以下海温的不对称性可能主要受到海洋内部非线性动力过程的影响。通过数值试验, 本文还发现热带印度洋海温的不对称性对气候平均态会有影响, 而这种不对称性长期积累后, 会导致上层热带印度洋温度层结趋于稳定状态。     

Variations in extratropical cyclone activity in northern East Asia

Based on an improved objective cyclone detection and tracking algorithm, decadal variations in extratropical cyclones in northern East Asia are studied by using the ECMWF 40 Year Reanalysis (ERA-40) sea-level pressure data during 1958-2001. The results reveal that extratropical cyclone activity has displayed clear seasonal, interannual, and decadal variability in northern East Asia. Spring is the season when cyclones occur most frequently. The spatial distribution of extratropical cyclones shows that cyclon...     

Effects of the Physical Process Ensemble Technique on Simulation of Summer Precipitation over China

The effects of the physical process ensemble technique on simulation of summer precipitation over China have been studied by using a p-σregional climate model with 9 vertical levels（pσ-RCM9）.The results show that there are obvious differences among simulations of summer precipitation over China from different individual ensemble members.The simulated precipitation over China is sensitive to different cumulus convection,radiative transfer,and land surface process parameterizations.These differences lead to large uncertainties in the simulation results.The standard deviation of the simulated summer precipitation departure percentage over West China is larger than that over East China,signifying that the simulated precipitation over East China has higher reliability and consistency than that over West China.The Talagr and diagram shows that the ensemble system has reasonable dispersion in the simulated summer mean precipitation over East China.The summer ensemble mean precipitation over East China evaluated by various indices is better than most single simulations.The physical process ensemble technique reduces the uncertainties of the model physics in precipitation and improves the simulation results as a whole.Further, adopting the optimized ensemble mean method can obviously improve the performance of the pσ-RCM9 model in simulation of summer precipitation over East China.     

一种依据初始场构造的参考大气廓线及对高原地区预报的影响

地形追随坐标系下的动力学方程组通常都要引入参考大气的概念来减少气压梯度力的计算误差.参考大气的一般取法是满足静止和静力平衡关系,实际大气被看成在参考大气上的偏差.实际大气与参考大气越接近,它们之间的偏差就越小,计算就越精确.参考大气的取法一般有等温大气、定常温度廓线、初始资料进行水平平均的垂直温度廓线等.本文在一个非静力的中尺度模式中选取经过水平平均的初始温度场的垂直廓线构造模式的参考大气廓线.但是初始资料在三维空间是离散的,这里根据三次样条函数的分段连续光滑的性质,构造了随起报时间不同而不同的,只随高度变化的解析形式的参考大气廓线.构造的参考大气廓线完全满足静力平衡关系,方程中的静力平衡部分可以得到最大限度地扣除.试验表明,与等温大气相比,这种根据初始状态选取的参考大气和实际资料更接近,在大地形附近气压梯度力的计算误差更小,500 hPa高原附近的24 h气压预报更精确.