Dynamics of Axisymmetric Truncated Dynamo Models     

Covas  E.  Tavakol  R. 《Studia Geophysica et Geodaetica》1998,42(3):356-363

An important question regarding the study of mean field dynamo models is how to make precise the nature of their underlying dynamics. This is difficult both because relatively little is known about the dynamical behaviour of infinite dimensional systems and also due to the numerical cost of studying the related partial differential equations. As a first step towards their understanding, it is useful to consider the corresponding truncated models. Here we summarise some recent results of the study of a class of truncated axisymmetric mean field dynamo models. We find conclusive evidence in these models for various types of intermittency as well as multiple attractors and final state sensitivity. We also find that the understanding of the underlying dynamics of such dynamo models requires the study of a new class of dynamical systems, referred to as the non-normal systems. Current work demonstrates that these types of systems are capable of a novel type of intermittency and also of relevance for the understanding of the full axisymmetric PDE dynamo models.  相似文献   

Importance of no‐rain measurements on the comparison of radar and rain gauge rain rate     

Chulsang Yoo  Kyoungjun Kim  Jeongho Choi  Eunho Ha 《水文研究》2010,24(7):924-933

This study evaluated four possible cases of comparing radar and rain gauge rain rate for the detection of mean‐field bias. These four cases, or detection designs, consider in this study are: (1) design 1‐uses all the data sets available, including zero radar rain rate and zero rain gauge rain rate, (2) design 2—uses the data sets of positive radar rain rate and zero or positive rain gauge rain rate, (3) design 3—uses the data sets of zero or positive radar rain rate and positive rain gauge rain rate and (4) design 4—uses the data sets of positive radar rain rate and positive rain gauge rain rate. A theoretical review of these four detection designs showed that only the design 1 causes no design bias, but designs 2, 3 and 4 can cause positive, negative and negative design biases, respectively. This theoretical result was also verified by applying these four designs to the rain rate field generated by a multi‐dimensional rain rate model, as well as to that of the Mt Gwanak radar in Korea. The results from both applications showed that especially the design 4, which is generally used for the detection of mean‐field bias of radar rain rate, causes a serious design bias; therefore, is inappropriate as a design for detecting the mean‐field bias of radar rain rate. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Wind impact on pollutant transport in a shallow estuary   总被引：4，自引：0，他引：4  

XU Hongzhou  LIN Jing  SHEN Jian  WANG Dongxiao 《海洋学报(英文版)》2008,27(3):147-160

A three-dimensional numerical model, EFDC （ environmental fluid dynamics code） is applied to the Pamlico River Estuary （PRE） in eastern North Carolina of the United States to examine the wind impact on pollutant age distributions and residence time. A series of model experiments representing base case, remote-wind-induced water level set-up and local winds cases are conducted. Model results indicate that the pollutant mean age and the system residence time are functions of gravitational circulation in the PRE. The system responses to remote-wind-induced water level set-up are different in different portions of the PRE. Under such condition, dissolved substances in the upstream portion of the PRE have a younger age and shorter residence time （compared with the base case） , by contrast, they have a older age and longer residence time in the downstream portion of the PRE. Upriver and downriver local winds appear to have opposite impacts on pollutant age distributions. The substances are retained much longer within the PRE under upriver wind than those under downriver wind. The model results also suggest that across - river winds may lead to longer residence time through enhanced turbulence mixing, which slows down the gravitational circulation in the PRE.  相似文献   

AVERAGE GLOBAL LOCATIONS     

Robert S. Yuill 《The Professional geographer》1987,39(1):69-74

Global distributions are commonly described by maps and tables which emphasize the dispersion of a distribution. The Mean Spheroidal Center (M.S.C.) defines the average location of a world distribution. It is an objectively determined point within the sphere's surface. The M.S.C. calculations are demonstrated using the world's 25 largest cities in each of four time periods.  相似文献   

黄、渤海冷空气海浪场的集合预报试验   总被引：1，自引：0，他引：1  

王亚男  王庆元  刘彬贤 《海洋学报》2015,37(9):10-16

利用欧洲集合天气预报系统51个预报风场驱动SWAN海浪模式,对黄、渤海2013年12月-2014年2月期间受冷空气影响的海浪场进行数值模拟试验,并利用浮标观测资料对海浪集合预报结果进行初步检验分析,结果显示:从逐时平均偏差结果可知,24h预报时效内集合平均与控制预报性能相近,48~72h预报时效内,集合平均明显优于控制预报,但均比实况偏小;集合分位值(75、90百分位值和极端值)明显优于集合平均,且预报时效越长,优势越明显,集合预报极端值与实况相当或略偏大;从逐24h平均偏差结果可知,集合分位值(75、90百分位值和极端值)比集合平均和控制预报更接近实况。总的分析表明:集合分位值(75、90百分位值和极端值)对受冷空气影响的海浪场具有较强的分辨能力,可以提高对海浪场的预报水平,且有较好的应用潜力。  相似文献   

Evaluation of the “fishing down marine food web” process in the north-west of Persian Gulf(Khuzestan Province) during the period of 2002–2011     

MASHJOOR Sakineh  KAMRANI Ehsan 《海洋学报(英文版)》2015,34(10):103-110

The worldwide increase in commercial fisheries and its impact on ecosystems as well as inefficient fishery management have led to overfishing and frequent breakdown of traditional fish stocks.In this context,an analysis of Khuzestan inshore fisheries data covering the years 2002–2011,was conducted in reliance on testing for occurrence of the fishing down marine food webs(FDMFW) phenomenon in the North of Persian Gulf Large Marine Ecosystem(LME).In this study,the mean trophic level(m TL) and the fishing-in-balance(FIB)-index of Khuzestan landings during this period of time were estimated using the trophic level of 47 fishery resources.Increase in total landings(Y) was observed,which explained the high fishing yield in major fishery resources(especially demersal).Moreover,the moderates decreasing trend in m TL per decade,and the increasing trend in FIB-index were observed.The status of fishery resources in Khuzestan inshore waters(under exploited but not overexploited),the rise in Y,FIB and slightly drop in m TL can be considered as indirect indicators of the fishing impacts on the trophic structure of marine communities.Based on this result,probability occurrence of FDMFW process in Khuzestan inshore waters is low to some extent.However,we suggest that the goal of management programs in Khuzestan inshore waters should prevent the continuance of this trend in the long-term using an ecosystem-based approach.  相似文献   

新型张力腿式储油处理平台的动力响应分析     

岑皓  王克用  赵胜涛  张海燕 《海洋技术学报》2015,34(5):97-103

针对目前小油田早期生产中存在的不足,提出一种适用于浅水海域的新型张力腿式储油处理平台,该平台主要由储油箱、浮箱、吸力桩、系泊链和甲板结构构成,具备原油处理和储存功能。应用非线性时域耦合分析法,研究了有义波高、平均波周期、水深对该平台的运动响应和系泊链张力的影响。计算结果表明,波高对平台动力响应有较大影响,有义波高每增加0.4 m,平台水平位移相应增加0.408 m,而系泊链力随有义波高的增加呈准线性增大;波周期对平台水平运动影响显著,平均波周期从6.5 s逐级变化至8.5 s时,最大水平位移自3.760 m渐增至5.467 m,而波周期对系泊链力影响较小,变化率一般小于10%;该新型平台对水深大于20 m的浅水海域有良好的动力特性,而对水深小于20 m的海域却表现异常。因此,该新型张力腿式平台能满足水深不小于20 m浅海区的油田早期生产需要。  相似文献   

青岛近海大型水母漂移集合预测方法研究   总被引：1，自引：0，他引：1  

吴玲娟  高松  刘桂艳  白涛 《海洋预报》2015,32(2):62-71

考虑水母垂直运动等自主运动,基于集合预报和拉格朗日粒子追踪方法,建立青岛近海大型水母的集合漂移预测模型。并利用2012—2013年青岛近海水母实时监测数据和集合漂移预测模型,快速预测水母集合漂移轨迹、速度、趋势和可能影响范围等要素。通过分析水母监测数据和数值模拟结果,在水母如何自主运动及其机理尚不十分清楚的情况下,多轨迹漂移预测结果比单轨迹的更合理、科学、可信,能够传达更多的信息量,对水母灾害的应急处置更具有指导意义。  相似文献   

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林国标  刘立龙  蔡成辉  黎峻宇  黄良珂 《大地测量与地球动力学》2015,35(2):235-238

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一种多因子加权平均温度模型的构建方法     

李得宴  杨维芳  高志钰  蒋玉祥  李蓉蓉 《测绘科学》2021,46(3):73-79

针对在地基GNSS水汽反演的过程中,天顶湿延迟转换为大气可降水量时如何建立精确的大气加权平均温度(Tm)模型的问题,该文在建立Tm模型前全面考虑了对Tm有显著影响的变量并选择最优回归子集。但分析发现,最优回归子集中各变量之间存在较强的相关性,这将会导致变量之间存在多重共线性,从而影响模型的稳定性和可靠性。选择2013—2015年相关气象数据作为变量并应用岭回归的方法削弱变量之间的多重共线性,建立稳定的多因子Tm回归模型。并利用该模型分别预测2016年1—12月、2019年1—7月的Tm,均方根误差分别为2.3 K和2.0 K,预测精度较高,这将为高精度的水汽反演奠定较好的数据基础。  相似文献