Simulations of Hydrological Cycle Changes Between the LGM and the Present Day over China     

LIU Yu  LI Weiliang  HE Jinhai  CHEN Longxun 《Acta Meteorologica Sinica》2010,24(5):641-656

Based on the International Satellite Cloud Climatology Project (ISCCP) data in 1983–2006,it is found that there is a high value center of high cloud amount over the Tibetan Plateau (TP),while there is a high value center of middle cloud amount over the Sichuan Basin extending to the coastal area of southeastern China along the same latitude,and a low one over the TP.The present day (PD) and Last Glacial Maximum (LGM) climates are simulated by using the NCAR Community Climate Model (CCM3) nested with a regio...  相似文献   

Impulse response of a linear diffusion analogy model as a flood frequency probability density function     

WITOLD G. STRUPCZEWSKI  VIJAY P. SINGH  STANISLAW WEGLARCZYK 《水文科学杂志》2013,58(5):761-780

Abstract

The impulse response of a linear convective-diffusion analogy (LD) model used for flow routing in open channels is proposed as a probability distribution for flood frequency analysis. The flood frequency model has two parameters, which are derived using the methods of moments and maximum likelihood. Also derived are errors in quantiles for these parameter estimation methods. The distribution shows that the two methods are equivalent in terms of producing mean values—the important property in case of unknown true distribution function. The flood frequency model is tested using annual peak discharges for the gauging sections of 39 Polish rivers where the average value of the ratio of the coefficient of skewness to the coefficient of variation equals about 2.52, a value closer to the ratio of the LD model than to the gamma or the lognormal model. The likelihood ratio indicates the preference of the LD over the lognormal for 27 out of 39 cases. It is found that the proposed flood frequency model represents flood frequency characteristics well (measured by the moment ratio) when the LD flood routing model is likely to be the best of all linear flow routing models.  相似文献   

Cosmogenic isotope (Cl) surface exposure dating of the Norber erratics, Yorkshire Dales: Further constraints on the timing of the LGM deglaciation in Britain     

Peter J. Vincent  Peter Wilson  Tom C. Lord  Christoph Schnabel 《Proceedings of the Geologists' Association. Geologists' Association》2010,121(1):24-31

Cosmogenic isotope (³⁶Cl) surface exposure dating of four of the erratic boulders at Norber in the Yorkshire Dales National Park, northwest England, yielded mean ages of ∼22.2 ± 2.0 ka BP and ∼18.0 ± 1.6 ka BP for their emplacement. These two mean values derive from different ³⁶Cl production rates used for exposure age calculation. The ages are uncorrected for temporal variations in production rates and may underestimate the true ages by 5-7%. The former age, although implying early deglaciation for this area of the British ice sheet, is not incompatible with minimum deglaciation ages from other contexts and locations in northwest England. However, the latter age is more consistent with the same minimum deglaciation ages and geochronological evidence for ice-free conditions in parts of the northern sector of the Irish Sea. Within uncertainties, the younger of the mean ages from Norber may indicate that boulder emplacement was associated with North Atlantic Heinrich event 1. The limited spatial (downvalley) extent of the Norber boulders implies that at the time of their deposition the ice margin was coincident with the distal margin of the erratic train. Loss of ice cover at Norber was followed by persistent stadial conditions until the abrupt opening of the Lateglacial Interstadial when large carnivorous mammals colonised the area. The ³⁶Cl ages are between ∼3.0 ka and ∼13.0 ka older than previous estimates based on rates of limestone dissolution derived from the heights of pedestals beneath the erratics.  相似文献   

中国单季稻种植北界的初步研究   总被引：3，自引：2，他引：1  

段居琦  周广胜 《气象学报》2012,70(5):1165-1172

确定单季稻种植北界可为调整单季稻生产布局和科学应对气候变化提供依据.基于中国单季稻种植区地理分布及其主导气候因子,结合最大熵模型,研究了雨养(水热共同作用)与灌溉(热量限制)条件下中国单季稻种植区的北界,并与已有方法确定的中国单季稻北界进行了对比验证.结果表明:雨养条件下,中国单季稻种植北界可达黑龙江漠河县北部,沿漠河—塔河—呼玛中部以西的大兴安岭地区及龙江—泰来—杜尔伯特—大庆—肇州—肇源以西的地区不适合种植水稻;灌溉条件下中国单季稻种植的北界则不存在,即在中国最北部的漠河地区仍可种植单季稻,沿漠河—塔河—呼玛中部的水稻种植界限往西略有偏移.本研究确定的中国单季稻种植北界与当前单季稻种植北界更为接近,明显优于已有方法确定的单季稻种植北界.  相似文献   

北京1841年以来均一化最高和最低气温日值序列的构建   总被引：1，自引：0，他引：1  

司鹏  郭军  赵煜飞  王冀  曹丽娟  王敏  王琪  冯婧 《气象学报》2022,80(1):136-152

长期连续的日值观测资料是研究百年来极端气候事件及其变化特征的重要基础支撑.目前中外由于缺乏可靠的逐日百年尺度气候资料,使得20世纪50年代以前的极端气候变化规律仍然没有得到很好的认识.基于国家气象信息中心收集整理的日最高和最低气温观测资料,构建北京1841—2019年气温日值序列.首先,通过数据质量控制剔除原始基础资料...  相似文献   

应用贝叶斯动态模型的地基沉降概率分析与预测   总被引：1，自引：0，他引：1  

魏冠军  党亚民  章传银 《测绘科学》2012,37(2):52-53,90

考虑到地基沉降预测模型中参数的时变特性及预测结果的可靠性,本文提出地基沉降概率预测方法:运用贝叶斯动态模型建立地基沉降过程的状态方程和观测方程,利用参数先验信息并结合含有噪声的前期沉降观测数据,对沉降状态参数进行Bayes后验概率推断,通过不断的"概率预测-修正"递推运算,获得最优沉降状态概率估计来预测地基沉降量。数值实例结果表明,与其他预测方法相比较,本文的方法是可行有效的。  相似文献   

水文频率分析中参数估计SAGA-ML方法的研究     

桑燕芳  王栋  吴吉春 《水文》2009,29(5)

建立基于模拟退火遗传算法(Sjmualted Annealing Genetic Algorithm,SAGA)的改进极大似然法,即将似然函数相反数求解极小值的表达式作为目标函数,依据矩法估计参数取值范围作为约束条件,然后应用SAGA进行参数估计.与常规极大似然法思路有本质不同,改进极大似然法通过遗传算法进行参数优化.通过蒙特卡罗试验,验证了改进极大似然法在参数估计和不同频率设计值估计两个方面均具有很好的准确性,与基于最大熵原理的方法效果相当,优于其他方法;同时该方法不受线型类型、参数数目和约束条件的限制;可以避免应用常规极大似然法时出现似然方程无解等情况;且求解过程简便快捷,使极大似然法在理论上和实际应用中都成为有效的方法.  相似文献   

Relict rock glaciers as indicators of Mediterranean palaeoclimate during the Last Glacial Maximum (Late Würmian) in northwest Greece     

P. D. Hughes  P. L. Gibbard  J. C. Woodward 《第四纪科学杂志》2003,18(5):431-440

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Chronology of the last recession of the Greenland Ice Sheet   总被引：1，自引：0，他引：1  

Ole Bennike  Svante Bjrck 《第四纪科学杂志》2002,17(3):211-219

A new deglaciation chronology for the ice‐free parts of Greenland, the continental shelf and eastern Ellesmere Island (Canada) is proposed. The chronology is based on a new compilation of all published radiocarbon dates from Greenland, and includes crucial new material from southern, northeastern and northwestern Greenland. Although each date provides only a minimum age for the local deglaciation, some of the dates come from species that indicate ice‐proximal glaciomarine conditions, and thus may be connected with the actual ice recession. In addition to shell dates, dates from marine algae, lake sediments, peat, terrestrial plants and driftwood also are included. Only offshore and in the far south have secure late‐glacial sediments been found. Other previous reports of late‐glacial sediments (older than 11.5 cal. kyr BP) from onshore parts of Greenland need to be confirmed. Most of the present ice‐free parts of Greenland and Nares Strait between Greenland and Ellesmere Island were not deglaciated until the early Holocene. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Study of the electron density in MgO, (Mg0.963Fe0.037)O and Cu2O by the maximum entropy method and multipole refinements: comparison between methods     

M. Merli  A. Pavese  M. Ranzini 《Physics and Chemistry of Minerals》2002,29(7):455-464

 The electron densities determined by the maximum entropy method and by the multipole refinement approach are compared with each other, in terms of some topological properties according to the Bader formalism (Laplacian and eigenvalues of the Hessian matrix of the electron density at the critical points). The cases of MgO, (Mg,Fe)O and Cu₂O are examined. The best agreement is observed for the critical points along the Mg–O, (Mg,Fe)–O and Cu–O directions, whereas larger discrepancies occur at the other critical points. Plots of the electron densities generated by the maximum entropy method and the multipole formalism along the most representative crystallographic directions contribute to elucidating the comparison between approaches. Received: 3 July 2001 / Accepted: 7 March 2002  相似文献