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81.
A gamma distribution is one of the most frequently selected distribution types for hydrological frequency analysis. The bivariate gamma distribution with gamma marginals may be useful for analysing multivariate hydrological events. This study investigates the applicability of a bivariate gamma model with five parameters for describing the joint probability behavior of multivariate flood events. The parameters are proposed to be estimated from the marginal distributions by the method of moments. The joint distribution, the conditional distribution, and the associated return periods are derived from marginals. The usefulness of the model is demonstrated by representing the joint probabilistic behaviour between correlated flood peak and flood volume and between correlated flood volume and flood duration in the Madawask River basin in the province of Quebec, Canada. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
82.
Energetic particles in a turbulent medium can be subject to second-order Fermi acceleration due to scattering on moving plasma waves. This mechanism leads to growing particle momentum dispersion and, at the same time, increases the mean particle energy. In the most frequently met situations both processes can be represented by a single momentum diffusion term in the particle kinetic equation. In the present paper we discuss the conditions allowing the additional term for regular acceleration to arise. For forward-backward asymmetric scattering centres, besides the diffusive term one should explicitly consider the regular acceleration term in momentum space, which can consist of the first-order (∝ V), as well as the second-order (∝ V2) part in the wave velocity V. We derive the condition for the scattering probability in the wave rest frame requied for vanishing the regular acceleration term and provide a simple mechanical example illustrating the theoretical concepts. Finally, we address its possible role in cosmic ray acceleration processes. 相似文献
83.
本文分析了1989年3月9日,11日,13日与AR5395产生的耀斑成协的,叠加在2cm微波爆发上的具有双峰结构的准周期振荡.利用磁流环结合的非线性不稳定性机制,对等离子体和磁场相互作用的过程进行了定性的分析,并计算了几个有关的参数.最后进行了简单的讨论. 相似文献
84.
85.
玉龙喀什河是昆仑山北坡最大的河流——和田河的主要支流。玉龙喀什河同古孜洛克水文站夏洪严重。因此预测最大洪峰出现日期是十分有意义的。用灰色系统理论来预测最大洪峰出现日期,是以原始数据为基础,按累加生成,建立GM(1,1)模型,并通过模型求出平滑度,进而作相对误差检验,合格后再作预测。经过检验,预测基本上符合实际。 相似文献
86.
Hilbert-Huang变换能够定量描述非线性、非平稳复杂时间序列的时频特性,较传统分析方法更具优势。通过对时间序列进行EMD分解,得到变化过程的内在模态函数和趋势项函数,而后对各内在模态函数进行Hilbert-Huang变换,从而揭示出时间序列的多时间尺度特征。以黄河花园口站1952-2009年的年最大洪峰流量时间序列为例,对其进行多时间尺度分析,得到不同波动周期的振荡分量及趋势分量,具体分析了各分量的变化特征。结果表明,花园口年最大洪峰流量变化过程中存在准3.2a、准6.4a、准11.8a和准31.0a周期的波动,其中准3.2a和准6.4a的周期波动是引起原序列波动的主要原因,近60年来花园口年最大洪峰流量变化呈递减趋势,由此揭示了年最大洪峰流量变化过程的多时间尺度特征。在此基础上,探讨了各波动分量变化的影响因素,其变化与大气低频振荡、ENSO、太阳活动及气候变迁等因素有关。 相似文献
87.
88.
The impact of global warming on the warmest and coldest days of the annual cycle is explored according to an A2 scenario simulated
by the CNRM-CM3 climate model in the framework of the IPCC AR4 intercomparison. Given the multi-model spread in IPCC projections,
a validation strategy is proposed using the NCEP/NCAR reanalysis. Validation of the late twentieth century model climatology
shows that warm and cold model events are slightly too long and infrequent. Although interannual trends in the warm (cold)
day occurrence were positive (negative) only for six (three) of the nine considered sub-continental regions, simulated model
trends are always positive (negative). This different behaviour suggests that simulated non-anthropogenic decadal variability
is small relative to anthropogenic trends. Large-scale synoptic processes associated with European regional warm and cold
peaks are also described and validated. Regional cold peaks are better reproduced than warm peaks, whose intensity accuracy
is limited by other physical variables. Positive (negative) winter anomalies of sea and land surface temperature lead to summers
with severe (weak) temperatures. These inter-annual anomalies are generated by a persistent pressure dipole over Europe. Regarding
climate change, warm (cold) events will become more (less) frequent and longer (shorter). The number of warm days will largely
rise and the number of cold days will dramatically decrease. The intensity of warm days will be particularly pronounced over
Europe, given the projected summer drying in this region. However, according to the limited skill of the CNRM model, these
results must be considered with caution. 相似文献
89.
山峰加热效应的数值试验研究 总被引:2,自引:1,他引:1
已有的资料分析和理论研究表明,山峰加热效应是形成冬季兰州市白天脱地逆温的主要原因。本文利用中尺度数值模式MM5,从数值试验角度研究了兰州市白天温度场和环流场的结构特征。模拟结果表明:冬季,白天日出后的皋兰山峰相对于周围空气是一个热源,在环流场的配合下,皋兰山峰的暖空气向市区上空输送,与河谷温度较低的冷空气形成了白天的脱地逆温;理想"削山"试验的结果表明,山峰海拔越高的山体,加热效应越明显,山谷城市的大气逆温强度和稳定度随着山峰海拔高度的降低而减小。数值试验结果进一步验证和补充了观测和理论分析的结论。 相似文献
90.
In this work, we have studied the model of modified Chaplygin gas and its role in accelerating phase of the universe for anisotropic
model. We have assumed that the equation of state of this modified model is valid from the radiation era to ΛCDM model. We
have obtained the possible relation between the hessence and the modified Chaplygin gas. We have also use the statefinder
parameters for characterize different phase of the universe diagrammatically. 相似文献