沟岸侧蚀对泥石流不稳定动力过程的影响

泥石流作为非牛顿体,屈服应力大,运动过程通常不稳定。前人建立了许多模型来研究沟床揭底和堰塞体溃决对泥石流不稳定动力过程的影响,沟岸侧蚀对泥石流不稳定动力过程的影响研究较少。通过侧蚀为主的模型和完全底蚀的模型两种水槽实验的对比,针对泥石流的动力过程展开研究。实验发现两种工况条件下泥石流正应力和孔隙水压力随着龙头高度沿程波动性的增长而相应地波动性增大,但侧蚀作用使得这种波动特征更加明显。通过力学分析,证明侧蚀作用导致泥石流龙头的阻力更大,但是龙身颗粒和龙头颗粒的速度差更大,使得龙头附加坡降更大,因此,侧蚀作用使得泥石流龙头的平均速度更快。泥石流龙头浓度和容重的不断增大,使得阻力不断增大,阻力和动力的动态平衡关系是泥石流不稳定运动的原因之一。     

广西农业干旱动态评估模型

以自然条件下大气-作物-土壤系统的水量平衡方程为基础,结合广西干旱灾害特点,建立广西农业干旱评估模型。与广西历史农业旱情实况对比分析表明,该模型能够较客观、定量地对农业干旱的发生、发展过程进行逐日动态监测和灾中、灾后评估。     

围压-孔压改变条件下致密砂岩及泥页岩泊松比变化特征及机制

在围压(外压)或孔压(内压)发生变化的条件下,致密砂岩及泥页岩泊松比的变化特征及机制仍有待厘清.本研究从Terzaghi有效应力理论和国内学者提出的新有效应力概念出发,基于松辽盆地高台子组致密砂岩、青山口组泥页岩三向动、静态泊松比测定结果,剖析了两类岩石泊松比的变化特征及机制.岩石样品三向泊松比变化曲线的分布呈现显著的...     

相控震源对地震信号信噪比的改善研究

当测区噪声很强,采用组合震源工作仍然不能满足信噪比要求时,为进一步提高地震勘探信噪比,引入能形成定向地震波的相控震源.针对水平层状介质模型,对组合震源、相控震源地震进行了数值模拟,并定量计算了采用4,8,15,20单元的组合与相控震源地震数据的信噪比,同组合地震相比,相控地震使来自不同反射层的反射波信号的信噪比平均提高了154～990 dB.结果表明,相控震源地震得到的反射波信号信噪比高于组合地震,并且随着激震器数目增加,相控震源合成地震记录中的反射波地震数据信噪比明显提高.     

Sensitive response of desert vegetation to moisture change based on a near-annual resolution pollen record from Gahai Lake in the Qaidam Basin, northwest China

We present a 50-year pollen record at near-annual resolution from Gahai Lake in the Qaidam Basin on the northeastern Tibetan Plateau. Chronology of a 22-cm short core was established by ²¹⁰Pb and ¹³⁷Cs analysis. The pollen results at 0.5 cm intervals show large changes in Artemisia/Chenopodiaceae (A/C) ratios from < 0.2 to 0.95 in the last 50 years. High (low) A/C ratios represent increase (decrease) in steppe pollen production, which correspond to high (low) relative humidity observed at nearby Delingha weather station. On the basis of good correspondence with instrumental records and carbonate content from Gahai Lake, we conclude that A/C ratio is sensitive to moisture change and can be a very useful index in reconstructing paleoclimate of arid regions. Comparison with pollen and snow accumulation data from Dunde ice core suggests that effective moisture at low and high elevations shows the opposite relationship when mountain precipitation was extremely high, possibly due to topography-induced uplifting and subsiding air dynamics.     

陕西黄土高原人工林土壤干层及形成原因

1 Introduction Abroad, a lot of research on soil water removal, seeping and evaporation has been done (Ole, 1998; Rapp, 2000). A seeping model of soil water was suggested (Yuin, 1998) and it was known that water removal is very slow in the unsaturated zon…     

Toward an improved global network for determination of tropospheric ozone climatology and trends

An examination of typical tropospheric ozone variability on daily, monthly, annual and interannual timescales and instrumental precision indicates that the current ozonesonde network is insufficient to detect a trend in tropospheric ozone of 1% per year at the 2 level even at stations with records a decade in length. From a trend prediction analysis we conclude that in order to detect a 1% per year trend in a decade or less it will be necessary to decrease the time between observations from its present value of 3–7 days to 1 day or less. The spatial distribution of the current ozonesonde stations is also inadequate for determining the global climatology of ozone. We present a quantitative theory taking into account photochemistry, surface deposition, and wind climatology to define the effectively sampled region for an observing station which, used in conjunction with the instrumental precision and the above prediction analysis, forms the basis for defining a suitable global network for determining regional and global ozone climatology and trends. At least a doubling of the present number of stations is necessary, and the oceans, most of Asia, Africa, and South America are areas where more stations are most needed. Differential absorption lidar ozone instruments have the potential for far more frequent measurements of ozone vertical profiles and hence potentially more accurate climatology and trend determinations than feasible with ozonesondes but may produce a (fair weather) biased data set above the cloud base. A strategy for cloudy regions in which either each station utilizes both lidars and sondes or each station is in fact a doublet comprised of a near-sea-level lidar and a proximal-mountain-top lidar could serve to minimize this bias.     

青藏高原地区OLR与地面有效辐射关系的分析

青藏高原;;OLR;;地面有效辐射     

中国人类生物气候区划初探

为研究气温，湿度，风速和太阳辐射对人体冷热感的综合影响，利用有效温度和风冷指数以及我国６５７个气象站３０年的气候资料，做了中国人类生物气候区划。结果表明，我国冬季大致可分为２７个生物气候区，夏季一般可分为２０个生物气候区。区划结果对旅行，定居，城市建设，事行动等人类活动有参考价值。