一种基于Helmert方差分量估计的Vondrak滤波方法

从基于Helmert方差分量估计的Vondrak滤波方法(简称HVF法)的基本假设入手,介绍了HVF方法,该方法能够在未知拟合函数的情况下,通过自动选择合理的平滑因子控制数据平滑的程度,对时序数据序列进行合理平滑,最大限度的削弱数据序列中的随机误差,将信号与噪声合理分离.     

泰山顶部近地层风的方差与谱分析

风在速度与方向上的不稳定性可引发结构振动并可导致损坏。山顶风较少受局地作用影响, 流场较稳定，作为典型风况对山顶风湍流脉动情形进行的观测和分析，对于研究建筑结构风载振动情形有着重要意义。在不同风况下对泰山气象站近地层风的风速和风向进行了同时、逐秒测记，所得样本经检验符合正态分布。计算表明，风向样本方差显著大于风速样本方差。绘制了各风速、风向样本自、互谱密度曲线图。谱图显示诸样本具有红噪声序列特征，不同样本自、互谱密度曲线具有相近形状，而以风速自谱曲线吻合程度最好，谱密度曲线在周期为4秒及2秒处有峰值。此后的研究应结合记录仪器的改进增加采样频率，对周期为2秒以下谱曲线作进一步分析。     

The separation of the influence of nutrients and climate on the varve time-series of baldeggersee, Switzerland

The varve data-set from a freeze-core taken in the deepest part of Baldeggersee was subjected to different multivariate statistical analyses in order to estimate the amount of variance in the varve thickness measures explicable by past climate and by the trophic state of the lake. A comparison of two different time-periods (1902 to1992 versus 1920 to 1980) revealed that the lake restoration programme since 1982 has had a significant impact on the formation of the seasonal layers. Results of the partitioning of the variance in the varve thickness measures showed that about two thirds of the variance are unexplained by a climate and trophic state model and that trophic state explains 6%, whereas climate accounts for about 28% of the variance before the effect of lake restoration had a strong impact on the varves. Among the climate parameters the amount of annual precipitation is a strong predictor for explaining the thickness of both dark layer and total couplet thickness, whereas summer precipitation is important for the thickness of the light layer.     

统一方差分量估计公式

本文提出了一种适用于协方差阵奇异或非奇异、设计阵列满秩或降秩时的方差分量估计方法;其公式推导简单,形式统一,不需解线性方程组,同时可保证迭代计算方差分量的非负要求。作为特例还和Helmert法及MINQUE法作了比较。最后讨论了用真误差进行方差分量估计的计算公式,并给出了一个测距误差分析的实例。     

我国太阳辐射量区域性变化特征研究*

对我国近35年来到达地面的太阳辐射量观测资料进行方差分析和统计检验,结果表明:从70年代开始,我国太阳直接辐射和总辐射量普遍减少,变化趋势分别为-246MJ/m2·10a和-16.8MJ/m2·10a,减少量最大中心在长江流域。太阳散射辐射量在东北、华北以及南方地区增加,在长江流域和西北地区减少。此外,用太阳辐射量倾向率的形式归纳出我国四种典型的区域性太阳辐射量季节变化特征。     

韶关市近50年强降水频数统计及周期分析

利用韶关市近50年降水资料,对逐日降水量R24（20～20时）≥50．0mm的强降水次数进行统计分析,结果表明韶关暴雨及以上强降水主要集中在多水期的3～7月,其中5、6月份为最多,这与韶关的自然季节降水特点是相吻合的;从50年代至90年代,各年代大暴雨和暴雨分别呈现出偏少．正常-正常-偏少-偏多和偏多～正常-偏少～偏少～偏多的演变趋势;R24≥50．0mm的强降水总次数及历年5、6月份R24≥50．0mm的强降水次数存在周期变化。     

Negative water vapour skewness and dry tongues in the convective boundary layer: observations and large-eddy simulation budget analysis

This study focuses on the intrusion of dry air into the convective boundary layer (CBL) originating from the top of the CBL. Aircraft in-situ measurements from the IHOP_2002 field campaign indicate a prevalence of negative skewness of the water vapour distribution within the growing daytime CBL over land. This negative skewness is interpreted according to large-eddy simulations (LES) as the result of descending dry downdrafts originating from above the mixed layer. LES are used to determine the statistical properties of these intrusions: their size and thermodynamical characteristics. A conditional sampling analysis demonstrates their significance in the retrieval of moisture variances and fluxes. The rapid CBL growth explains why greater negative skewness is observed during the growing phase: the large amounts of dry air that are quickly incorporated into the CBL prevent a full homogenisation by turbulent mixing. The boundary-layer warming in this phase also plays a role in the acquisition of negative buoyancy for these dry tongues, and thus possibly explains their kinematics in the lower CBL. Budget analysis helps to identify the processes responsible for the negative skewness. This budget study underlines the main role of turbulent transport, which distributes the skewness produced at the top or the bottom of the CBL into the interior of the CBL. The dry tongues contribute significantly to this turbulent transport.     

THE QUALITY OF MEAN AND VARIANCE ESTIMATES FOR NORMAL AND LOGNORMAL DATA WHEN THE UNDERLYING DISTRIBUTION IS MISSPECIFIED

Theoretical and simulation results are employed to evaluate mean and variance estimaies for normal datawhen a lognormal distribution is assumed and for lognormal data when a normal distribution is assumed.Misspecifying the distribution leads to the use of suboptimal estimation methods.However,the resultsshow that the suboptimal methods still produce estimators of good quality(low bias and variance)relativeto the minimum variance unbiased estimators for each distribution,at least when practical efficiency isconsidered.     

Variance Method to Determine Turbulent Fluxes of Momentum And Sensible Heat in The Stable Atmospheric Surface Layer

Evidence is presented that in the stable atmospheric surface layer turbulent fluxes of heat and momentum can be determined from the standard deviations of longitudinal wind velocity and temperature, σ _u and σ _T respectively, measured at a single level. An attractive aspect of this method is that it yields fluxes from measurements that can be obtained with two-dimensional sonic anemometers. These instruments are increasingly being used at official weather stations, where they replace the standard cup anemometer–wind vane system. With methods such as the one described in this note, a widespread, good quality, flux network can be established, which would greatly benefit the modelling community. It is shown that a ‘variance’ dimensionless height (ζ _σ) defined from σ _u and σ _T is highly related to the ‘conventional’ dimensionless stability parameter ζ=z/L, where z is height and L is the Obukhov length. Empirical functions for ζ _σ are proposed that allow direct calculation of heat and momentum fluxes from σ _u and σ _T. The method performs fairly well also during a night of intermittent turbulence.     

河西走廊下垫面粗糙度实测值与模拟值的差异性分析

利用甘肃省河西地区17个风塔观测资料和风向风速标准差法,计算了风塔处的下垫面粗糙度,并与中尺度数值模式ARPS中使用的粗糙度参数进行了比较分析。结果表明,数值模式中使用的粗糙度值和实况具有一定差异,其使用的粗糙度定义方案并不能准确地反映出下垫面粗糙度和非均一性特征。差异最大出现在草原下垫面上,可达375%,且差异程度随下垫面植被复杂程度增加。