Extreme rainfall events in Catalonia. The case of 12 November 1988     

M. Carmen Llasat  Roberto Rodriguez 《Natural Hazards》1992,5(2):133-151

A study of the synoptic situation which produced the catastrophic floods of November 1988 in Catalonia (in the northeast of the Iberian Peninsula) is presented. Analyses of the vertical structure, potential instability, precipitable water, and instability index are made through the radiosounding data from Palma, Majorca. It is found that the 1988 situation is included in type I intense convective events in Catalonia (classification obtained from all the events since 1950, (Llasat, 1989)). It was characterized by:

(a)	-pattern in the middle and high troposphere, the ridge axis east of Catalonia.
(b)	High pressure over Europe.
(c)	South-easterly winds in the lower troposphere with warm and moist humid air advection and south-westerlies aloft over Catalonia.
(d)	Strong instability (convective and latent).
(e)	Penetration of Atlantic air.

  相似文献   

胡杨根系分布特征与根系吸水模型建立   总被引：16，自引：1，他引：15  

冯起  司建华  李建林  席海洋 《地球科学进展》2008,23(7):765-772

依据2006年和2007年6~7月在极端干旱区额济纳的实测资料,利用分形和概率统计的方法对胡杨根系分布与根区土壤水分的关系进行了分析研究。引入土壤含水率期望(cm·g/g)的概念,建立了含水率期望值与根系分维值之间的函数关系,并求出了适宜胡杨生长的土壤含水率期望值的范围。同时建立了初版的根系吸水模型,并进行验证,得到较好的结果。  相似文献   

Governing fisheries as complex adaptive systems     

Robin Mahon  Patrick McConney  Rathindra N. Roy 《Marine Policy》2008

Fisheries are complex human-in-nature systems. The conventional approach to fisheries systems has been to treat them as predictable and controllable. As complex systems they are neither of the two and have to be approached differently. Complex systems often exhibit the capacity to self-organize or adapt, even without outside influence. If this is true of fisheries, it should lead to a radically different approach to management of fisheries systems that places much emphasis on enabling self-organization, learning and adaptation. Conceptual and practical frameworks for enabling activities are needed.  相似文献   

基于主成分-正则化极限学习机的超高密度电法非线性反演   总被引：2，自引：0，他引：2       下载免费PDF全文

江沸菠  戴前伟  董莉 《地球物理学报》2015,58(9):3356-3369

超高密度电法是一种新的地球物理探测技术,它通过多通道数据采集和多装置数据联合反演,极大地提高了电法勘探的成像精度.本文提出一种主成分-正则化极限学习机(PC-RELM)非线性反演方法,该方法针对超高密度电法所获取的高维勘探数据进行反演建模,通过随机设定隐层参数来简化模型的学习过程,通过主成分分析方法来进行高维数据降维,最后引入正则化因子提高反演模型的泛化能力.论文给出了超高密度电法的原理、样本构造方法和非线性反演流程,使用交叉验证方法获得了优化的隐节点数目和正则化参数,构造了优化的反演模型.通过两个经典的超高密度模型的反演结果表明,该方法能够较好地解决超高密度电法反演的高维数据非线性建模问题,能够弥补单一装置数据反演的不足,同时相较其他的非线性反演方法(ELM,BPNN和GRNN)具有更加准确的反演结果.  相似文献   

基于土壤反射光谱特性的广东省稻田土壤快速分类   总被引：1，自引：0，他引：1  

李丹  彭智平  韩留生  王重洋  刘尉  黄思宇  陈水森 《热带地理》2015,35(1):29-34

选择广东省215个村镇稻田的土壤样本,首先利用ASD Field Spec3测量土壤样本在350~2 500 nm的光谱,并采用S-G一阶导数平滑滤波降低样本测量中光照差异的影响,然后将遗传算法（Genetic Algorithm,GA）和支持向量机分类（Support Vector Machine,SVM）分别用于提取分类光谱特征和建立分类模型,分别在土纲、亚纲、土类3个层次进行土壤分类。结果表明：1）在不同的分类层次下,与铁氧化物密切相关的650~710以及900 nm附近光谱,与羟基矿物吸收有关的2 207~2 237和2 377~2 397 nm区间均被作为分类特征变量。2）随着土壤类型的细分,分类所需变量增多。在土类级,对有机质敏感的2 080 nm附近的光谱也被引入分类定标模型中,土纲和亚纲下分类精度＞67%,土类级分类精度为58.67%。利用遗传算法提取光谱特征,进行基于支持向量机的土壤分类具有一定优势。  相似文献   

湖南省极端降水过程客观监测指标     

廖玉芳  张剑明  刘兵  李英  唐爱军  段丽洁 《气象与环境学报》2014,30(5):146-152

利用1981-2010年湖南省97个地面气象观测站降水观测资料,基于二阶求导和尖顶突变模型等方法,分别对短历时降水序列和过程降水序列进行时间突变分析。结果表明：不同时间的最大小时累积降水量在时间上的突变点分别为12.0 h、6.1 h;过程降水持续时间突变点分别为10.0 d、4.4 d,不同持续时间最大降水量占过程总降水量的百分比及最大降水量在时间序列上的突变点分别为10.0 d、4.6 d和10.0 d、4.9d。建立的湖南省极端降水过程客观监测指标为：连续1-6 h、12 h最大降水量,连续1-5 d、10 d最大降水量和过程累积降水量及降水持续时间。指标的适用性通过与农作物因洪涝灾害的受灾率、成灾率及单位面积粮食减产量的相关分析验证。  相似文献   

云南天文台1m红外望远镜的主镜热力学分析     

顾伯忠  左恒 《天文研究与技术》2008,5(1):83-90

云南天文台1m红外太阳望远镜是多功能、多波段的太阳望远镜,望远镜使用过程中主镜的热变形直接关系这系统的光学精度,建立光学系统的光机热结合的分析方法,可以直观的得到热辐射对光学系统的影响结果,使得望远镜的设计阶段就能评估热变形对系统的精度影响,确定光学元件是否满足要求.  相似文献   

Multi-step prediction of strong earthquake ground motions and seismic responses of SDOF systems based on EMD-ELM method     

《Soil Dynamics and Earthquake Engineering》2016

This paper proposes a new multi-step prediction method of EMD-ELM (empirical mode decomposition-extreme learning machine) to achieve the short-term prediction of strong earthquake ground motions. Firstly, the acceleration time histories of near-fault ground motions with nonstationary property are decomposed into several components of intrinsic mode functions (IMFs) with different characteristic scales by the technique of EMD. Subsequently, the ELM method is utilized to predict the IMF components. Moreover, the predicted values of each IMF component are superimposed, and the short-term prediction of ground motions is attained with low error. The predicted results of near-fault acceleration records demonstrate that the EMD-ELM method can realize multi-step prediction of acceleration records with relatively high accuracy. Finally, the elastic and inelastic acceleration, velocity and displacement responses of single degree of freedom (SDOF) systems are also predicted with satisfactory accuracy by EMD-ELM method.  相似文献   

Recent trends of extreme temperature indices for the Iberian Peninsula     

《Physics and Chemistry of the Earth》2016

Climate change and extreme climate events have a significant impact on societies and ecosystems. As a result, climate change projections, especially related with extreme temperature events, have gained increasing importance due to their impacts on the well-being of the population and ecosystems. However, most studies in the field are based on coarse global climate models (GCMs). In this study, we perform a high resolution downscaling simulation to evaluate recent trends of extreme temperature indices. The model used was Weather Research and Forecast (WRF) forced by MPI-ESM-LR, which has been shown to be one of the more robust models to simulate European climate. The domain used in the simulations includes the Iberian Peninsula and the simulation covers the 1986–2005 period (i.e. recent past). In order to study extreme temperature events, trends were computed using the Theil-Sen method for a set of temperature indexes defined by the Expert Team on Climate Change Detection and Indices (ETCCDI). For this, daily values of minimum and maximum temperatures were used. The trends of the indexes were computed for annual and seasonal values and the Mann-Kendall Trend test was used to evaluate their statistical significance. In order to validate the results, a second simulation, in which WRF was forced by ERA-Interim, was performed. The results suggest an increase in the number of warm days and warm nights, especially during summer and negative trends for cold nights and cold days for the summer and spring. For the winter, contrary to the expected, the results suggest an increase in cold days and cold nights (warming hiatus). This behavior is supported by the WRF simulation forced by ERA-Interim for the autumn days, pointing to an extension of the warming hiatus phenomenon to the remaining seasons. These results should be used with caution since the period used to calculate the trends may not be long enough for this purpose. However, the general sign of trends are similar for both simulations despite some differences in their magnitudes.  相似文献   

120°E赤道电离异常区电子浓度总含量分析与预测          下载免费PDF全文

徐振中  王伟民  王博  杨升高 《地球物理学报》2012,55(7):2185-2192

基于国际全球定位服务中心(International GPS Service,IGS)提供的120°E 上空1999-2009年IONEX格式电离层电子浓度总含量(TEC)资料,分析赤道电离异常驼峰区TEC峰值Inc和Isc的年变化和季节变化以及与太阳、地磁活动的相关性.在11年时间尺度上,Inc和Isc与太阳辐射P指数的日均值有较好的相关性(r=0.90和r=0.84),而与地磁活动指数Dst、Kp和Ap日均值的相关性均不好.驼峰区TEC峰值Inc和Isc都是在北半球春、秋季出现极大值,而且冬季值大于夏季值,即Inc呈现"半年异常"和"冬季异常"现象,我们认为Inc和Isc相似的半年变化特征是与赤道上空电离层电急流相关的东向电场半年变化导致的.利用支持向量回归方法构建了EIA指数的预报模型,预报试验结果表明,该预报模型能较准确地描述Inc和Isc的变化,对南北驼峰TEC峰值预报的平均相对误差分别为22.96%和10.2%.基于支持向量机回归的预测方法为赤道电离异常特征指数预报的实现提供一条有效方法途径和好的应用前景.  相似文献