On the impact of cloudiness on the characteristics of nocturnal downslope flows

The effects of cloud cover amount and the height of cloud base on nighttime thermally induced downslope flow were investigated using analytical and numerical model approaches. The conclusions obtained with the analytical and the numerical model evaluations agreed. It was concluded that, (i) as cloud cover increases and/or the height of cloud base decreases, the depth and the intensity of nighttime thermally-induced downslope flows may decrease by a factor reaching one sixth and one tenth, respectively, in the case of overcast low cloud; (ii) when skies suddenly cloud over around midnight, the development of the downslope flow is altered in different ways: a reduction in intensity; or a cessation of further development, depending on the fraction of cloud coverage, and (iii) with a sudden clearing of overcast low cloud around midnight, the depth and the intensity of the downslope flow increases significantly.On leave from the Institute of Atmospheric Physics, Academia Sinica, Beijing, China.On leave from CSIRO, Division of Atmospheric Research, Private Bag No. 1, Mordialloc, Victoria 3195, Australia.     

气枪震源弱信号提取的可靠性初步分析

基于数据合成仿真、气枪震源激发信号的实际处理,由叠加信噪比、波形相关系数及相位偏移等3个定量指标,系统评价线性、相位加权和S变换等3种叠加方法提取强背景噪声下弱信号的实际性能,并定量估计叠加结果的可靠性。通过对以上3种方法叠加结果的综合探讨,初步对比分析后认为,线性叠加虽然信噪比较低,但波形畸变最小;相位加权叠加信噪比较高,相位偏移小,但波形质量与线性叠加的结果相比偏离较大;S变换叠加可获得相对较高的信噪比,波形幅度损失小,但存在一定的相位偏移现象。因此建议,当波形质量和时间精度均要求较高时宜用线性叠加。但气枪震源激发有限时选择叠加方法应有所偏重,若要求波形高保真,宜选择S变换叠加;若要求时间高精度,可选择相位加权叠加方法,以合理实现弱信号的有效提取。     

国家地震速报备份系统的部署与运行

国家地震速报备份系统是由中国地震局出资,在广东省地震台网中心建设的一套全自动地震速报系统.本文介绍了国家地震速报备份系统的职责、系统架构、主要功能模块、系统工作原理、部署情况与台网规模,分析了系统2009-2010年运行两年来的工作情况,并对系统自动产出的地震定位结果进行初步的统计与比较,对系统运行的总体效果给予了初步...     

资源丰裕程度与经济发展关系的探讨——资源诅咒效应国内研究综述

从资源诅咒的存在性实证检验,资源诅咒的传导机制以及如何解决资源诅咒现象3个方面对国内文献进行总结。结果表明,国内目前对资源诅咒的研究成果尚未形成系统,并且相关研究主要集中在经济学领域,因此,资源诅咒现象依然有待各位学者,尤其是地理学者从区域的角度不断进行探索。     

城市雨水地下回灌过程中悬浮物表面堵塞规律

雨洪资源地下回灌是缓解城市供水压力、解决地下水过量开采引起环境负效应的有效途径之一,但堵塞问题却是制约回灌技术推广的关键问题。基于前人理论,研究了入渗介质与悬浮物粒径中值之比(D₅₀/d₅₀)对堵塞层空间分布的影响。以建立表面堵塞预测模型为目的,利用城市雨水回灌细粒石英砂介质开展室内实验,观测雨水回灌的表面堵塞过程并获取渗透性变化的观测数据。根据物理、化学与生物堵塞的产生条件及堵塞特点,判断雨水回灌产生的堵塞性质为物理堵塞。引入过滤模型描述堵塞的发展过程,确定了模型用于模拟细砂表面堵塞的参数值：孔隙堵塞系数（α）为0.15 m²/kg,阻力增长系数（f′R′）为20 000 m/kg。在不改变以上2个参数值的条件下,用该模型模拟不同悬浮物粒径悬浊水回灌细粒石英砂的堵塞过程,取得了较好的拟合效果。此过滤模型可以用于模拟入渗介质与悬浮物粒径D₅₀/d₅₀值小于5的表面堵塞的发展过程,可定量预测堵塞对回灌速率的影响。     

A double-differenced cycle slip detection and repair method for GNSS CORS network

The difficulty to detect and repair cycle slip of carrier phase measurements is a key limit for continuously high accuracy of GNSS positioning and navigation services. We propose an automated cycle slip detection and repair method for data preprocessing of a CORS network. The method jointly uses double-differenced (DD) geometry-free (GF) combination and ionospheric-free observation corrected for the computed geometrical distance (IF-OMC) to estimate the cycle slips in dual-frequency observations. The DD GF combination, which is only affected by the ionospheric residual, can be used to detect cycle slips with high reliability except for special pairs such as (77, 60) on GPS L1/L2 frequencies. The detection principle of the IF-OMC observable is such that there is a large discontinuity related to the previous epoch when cycle slips occur at the present epoch. The disadvantages of these two combinations can be overcome employing the proposed detection method. The cycle slip pair (77, 60) has no effect on the GF combination, while a change of 14.65 m is derived from GPS L1/L2 observations using the IF-OMC algorithm. Using pre-determined station coordinates as precise values, we found that the accuracy of the DD IF-OMC combination was 18 mm for a 200-km CORS baseline. Therefore, cycle slips in dual-frequency observations can be correctly and uniquely determined using DD GF and IF-OMC equations. The proposed method was verified by adding simulated cycle slips in observations collected from the CORS network under a quiet ionosphere and shown to be effective. Moreover, the method was assessed with observations made during intense ionospheric activity, which generated extensive cycle slips. The results show that the algorithm can detect and repair all cycle slips apart from two exceptions relating to long data gaps.     

Determination of trace and rare-earth elements in Chinese soil and clay reference materials by ICP-MS

Inductively coupled plasma mass spectrometry(ICP-MS) has become a powerful tool for providing reliable analytical results in many laboratories around the word. In this study, the mixture of HF and HNO3 acids in high-temperature and high-pressure closed-vessel digestion technique were used to decompose some Chinese reference materials, and thirty seven elements were determined by ICP-MS. Most of the results for Chinese soil reference materials were found to be in reasonable agreement with the reference values, except Cs, Ta, Li, Ge, Zn, Nd, Tb and Ta whose values need to be revised. Their precisions were typically lower than 5% RSD. However, the Precisions of Chinese clay reference materials, especially for GBW03102 and GBW03102a, were significantly different with reference values, probably reflecting the existence of a coarser-grained fraction(70 μm) in samples, and the formation of fluorides in Al-rich samples during sample decomposition by using the mixture of HF and HNO3 acids. Moreover, thirty-seven trace elements covering the mass range from Li to U in four Chinese clay reference materials were firstly provided with good precision and accuracy in this study.     

第四纪沉积物天然热释光测量方法技术研究——山东草桥油田研究实例

第四纪沉积物天然热释光测量是一种累积间接油气勘查新方法。文中给出了首次系统研究的成果 ,从数百个样品中总结出的适用油气勘探的预热线形升温、恒温最佳加热程序 ,升温速率以 β=6℃ /s为宜 ,恒温温度 40 0℃ ,40 0℃恒温时间为 12s。在沉积物辐射剂量响应及日光晒退实验数据的基础上 ,总结了样品采集、预处理及测量方法。通过对山东草桥油田第四纪沉积物天然热释光与游离气烃野外实测资料的分析 ,发现天然热释光异常与气烃异常完全吻合 ,在油水边界上方 ,热释光、甲烷、乙烷出现高值异常 ,油田上方是低值带 ,为串珠状异常模式。热释光最大值为 2 0 4.2 μGy ,平均值为 79.45μGy ,标准差为 3 4 .14 μGy ;甲烷浓度异常下限为 2 5μL/L ,乙烷浓度异常下限为 4.4μL/L。     

大九湖泥炭地现代植物不同组分的δ18O特征及其古气候意义

最初学者利用泥炭植物同位素重建气候变化是参考树轮的研究方法,而树轮中不同组分的同位素对气候变化的响应不同。泥炭地植物不同组分的同位素对气候的响应是否也存在差异,需要进一步探讨和研究。此外,不同泥炭地植物δ¹⁸O的气候学解译存在一定的争议,这些解译的差异要求我们在利用泥炭δ¹⁸O重建古气候时需结合泥炭地现代过程的监测。文章以中国东部季风区的大九湖泥炭地为研究区域,测试研究区现代植被α纤维素与综纤维素的δ¹⁸O,对比两者的分布特征及其在时间序列上的相关性,进而探讨它们对气候因子的响应程度。结果表明：大九湖泥炭地植物δ¹⁸O分布较离散,平均值为25.09‰,α纤维素的δ¹⁸O比综纤维素δ¹⁸O偏正0.79‰~1.06‰,两种组分的δ¹⁸O在季节变化序列上没有明显的相关性。通过与区域气候因子的对比,我们发现温度是影响该地区植物δ¹⁸O变化的主要因素,而且植物α纤维素的δ¹⁸O比综纤维素的δ¹⁸O对温度响应更敏感,植物α纤维素更适用于作为研究古气候变化的载体,这一结果为中国东部季风内将泥炭地植物α纤维素的δ¹⁸O作为温度变化的代用指标提供了实验支持。

     

大自然的报复

四周漆黑一片,突然袭来的洪水冲走了一切,不见爸爸妈妈,6岁的小姑娘江珊在恐怖的大水中挣扎.