Snow Albedo’s Dependence on Solar Zenith Angle from In Situ and MODIS Data

Since snow cover is one of the fastest modi- fications to the land surface albedo, the treatment of snow-covered surface albedo is important for the simulation of land processes in weather and climate models. A simple formulation is developed here to represent the solar zenith angle (SZA) dependence of albedo under maximum snow cover condition on the basis of Moderate Resolution Imaging Spectroradiometer (MODIS) Bidirectional Reflectance Distribution Function (BRDF) algorithm. The SZA dependence of black-sky (or direct) albedo is weaker under snow condition than that under snow-free condition, and it does not differ much among different vegetation types. The blue-sky albedo (or combined albedo from direct and diffuse radiations) based on the above formulation and in situ diffuse ratio of solar radiation is consistent with in situ data from two Canadian sites (grassland and evergreen needleleaf forest) and one U.S. grassland site. In particular, the SZA dependence of blue-sky snow albedo is almost always weak because of high diffuse ratios for high SZA in winter. With the snow albedo formulation from this study and snow-free albedo formulations from the authors’ previous studies, albedos with partial snow cover can be obtained as the snow fraction-weighted average of snow and snow-free albedos. Citation: Wang, Z., and X. Zeng, 2008: Snow albedo’s dependence on solar zenith angle from in situ and MODIS data, Atmos. Oceanic Sci. Lett., 1, 45-50     

北方冬麦区遭受严重干旱

2009年1月我国主要气候特点:气温高但变化幅度大,降水少.全国平均气温为-4.8℃,较常年同期(-5.9℃)偏高1.1℃.全国平均月降水量为6.6mm,较常年同期(12.1mm)偏少5.5mm,为1987年以来历史同期最少值.     

利用地面电场仪与闪电定位资料进行短时雷电预警的方法

电场强度预警应以电场强度到达的门限等级、电场曲线初始阶段是否有快变抖动为判断的标准,雷电距离预警以雷电发生的位置和电场仪之间的距离为参考。综合两种预警手段,并结合人工判断雷电的移动趋势、对预警提前时间的要求以及电场仪安装的位置和本地的地形条件等因素,实现更准确的雷电短时预警。     

西藏南部晚始新世打拉埃达克质花岗岩及其构造动力学意义

打拉二云母花岗岩岩体位于雅拉香波穹隆的东南,侵入到中生代以前的变质岩系(眼球状花岗质片麻岩和石榴黑云母片麻岩)和特提斯沉积岩(页岩和砂岩)中,主要由石英、斜长石、钾长石、黑云母和白云母组成,形成于～44.3Ma。打拉二云母花岗岩地球化学特征表明:打拉花岗岩具有高Al_2O_3(16.0%～17.0%)、Na_2O/K_2O(1.2)以及A/CNK比值(1.05),表明打拉花岗岩为富钠过铝质花岗岩;轻稀土(LREE)富集,重稀土(HREE)相对亏损,HREE中的Ho到Lu元素有变平的特征((Ho/Lu)_N=1.11～1.46);具有微弱或无Eu异常,Eu/Eu~*=0.87～0.95;较高的初始Sr同位素比值(~(87)Sr/~(86)Sr(i)=0.71754～0.71785)和较低的初始Nd比值(ε_(Nd)(i)=-9.15～-12.4)。打拉花岗岩具有高Sr含量(为355×10~(-6)～416×10~(-6))和Sr/Y的比值(59.1～71.5)、高La/Yb比值、低Y及HREE亏损的特征,与埃达克质花岗岩类似。上述特征表明打拉花岗岩是在较高压力条件下,以角闪岩为主的深部岩石部分熔融的结果。     

基于物元理论的滑坡灾害易损性分析及其防灾减灾对策——以湖南湘西为例

物元分析是解决矛盾问题的规律和方法,是系统科学、思维科学和数学的交叉学科。本文简单分析了物元概念的可拓性,通过以湖南湘西为例,应用物元理论知识分析说明危岩、滑坡灾害的社会经济易损性具有发散性、可扩性、相关性和共扼性的特点,提出减灾工作应在传统理论研究的基础上,应用物元理论采用可拓学的方法科学地制定防灾减灾对策,以期为滑坡区域防灾、减灾规划工作提供新的理论和方法依据。     

灌浆钻灌一体化工艺实践与探讨

历来灌浆是由两个不同的工序组合起来的,即成孔与灌浆,成孔由一套钻具完成,灌浆又是由另一套灌浆管系列完成,之间无相联关系。因此,在某些施工区域,可由钻机组与灌浆组分别完成。通过工艺改进后,可将成孔与灌浆改为一个工序,使灌浆质量与效率均能得到提高。介绍了钻灌一体化技术的原理、工艺流程及其工艺特点,并列举了工程实例。     

A stochastic collocation based Kalman filter for data assimilation

In this paper, a stochastic collocation-based Kalman filter (SCKF) is developed to estimate the hydraulic conductivity from direct and indirect measurements. It combines the advantages of the ensemble Kalman filter (EnKF) for dynamic data assimilation and the polynomial chaos expansion (PCE) for efficient uncertainty quantification. In this approach, the random log hydraulic conductivity field is first parameterized by the Karhunen–Loeve (KL) expansion and the hydraulic pressure is expressed by the PCE. The coefficients of PCE are solved with a collocation technique. Realizations are constructed by choosing collocation point sets in the random space. The stochastic collocation method is non-intrusive in that such realizations are solved forward in time via an existing deterministic solver independently as in the Monte Carlo method. The needed entries of the state covariance matrix are approximated with the coefficients of PCE, which can be recovered from the collocation results. The system states are updated by updating the PCE coefficients. A 2D heterogeneous flow example is used to demonstrate the applicability of the SCKF with respect to different factors, such as initial guess, variance, correlation length, and the number of observations. The results are compared with those from the EnKF method. It is shown that the SCKF is computationally more efficient than the EnKF under certain conditions. Each approach has its own advantages and limitations. The performance of the SCKF decreases with larger variance, smaller correlation ratio, and fewer observations. Hence, the choice between the two methods is problem dependent. As a non-intrusive method, the SCKF can be easily extended to multiphase flow problems.     

广西六景泥盆系弗拉斯阶-法门阶界线层牙形石生物地层及碳同位素组成

广西六景泥盆系剖面是中国泥盆系标准剖面之一,通过对其弗拉斯阶-法门阶(F-F)界线附近地层进行详细的牙形石生物地层研究,自下而上识别出3个牙形石带:晚rhenana带、linguiformis带和triangularis带。F-F界线位于融县组下部(第7号层与第8号层之间),在谷闭组顶界之上3.32,m处。碳同位素的分析结果表明,F-F之交δ13C具有显著正偏移,增幅为2.0‰,与湖南老江冲、广西垌村和杨堤以及欧洲、美洲、非洲和澳洲等地的F-F界线附近的碳同位素记录一致,且具有相近的变化幅度。δ13C正异常与F-F界线上的生物灭绝有关,由于食微生物的高等生物灭绝,微生物大量繁盛,诱导海水缺氧,导致海洋有机碳埋藏速率增加,从而形成δ13C的正偏。F-F界线层发育一套以碎屑灰岩为特色的事件沉积,该事件沉积在广西乃至全球具有等时性,可能与小行星碰撞地球引起的全球性海啸有关。     

一个再生台风的分析

8214号台凤,不但路径奇异,而且生命史也奇特。本文利用GMS云图和常规的天气资料对其进行跟踪和分析,在揭示事实的基础上,着重对它的再生过程和在台风减弱阶段,中心从密蔽云区中外移且分离的现象进行探讨,得到一些有意义的结果。     

冬季中东急流与中国气候异常的联系

用NCEP/NCAR再分析资料和中国160站降水和气温资料,研究了冬季中东急流与中国气候异常的联系。结果表明:中东急流偏强、位置偏东南时,200 hPa上孟加拉湾、中南半岛及中国南海西风加强,而中国30°N以北西风减弱,相应地东亚急流减弱;500 hPa上西欧脊加强且东欧大槽加深,伴随孟加拉湾北部南支槽加深而东亚大槽减弱,有利于欧洲中东部冷空气频繁向东南方向活动,并一直影响到中国西南部;850 hPa上缅甸、中南半岛、华南沿海的西南风距平,有利于孟加拉湾水汽向华南地区输送;上述大气环流异常有利于华南地区降水显著增加,长江上游地区气温下降特别是西南地区气温显著降低,东北地区气温升高;反之亦然。