Rill erosion along the thalweg of a hillslope hollow: A case study from the cotswold hills,Central England

Rill erosion is an important erosional form on agricultural soils in England, causing large losses of soil, particularly on cultivated slopes. This paper describes a rill system that developed in a small agricultural catchment in north Oxfordshire during the winter of 1992–93. The rill system comprised two components: a system of ‘feeder rills’ along the valley-side slopes, which were the result of flow concentration and erosion along wheelings, and a thalweg rill, which formed along a dry valley bottom as a result of surface runoff concentration from the feeder rills. Total volumetric soil loss from the rill system was 32·28 m³, equivalent to 3·01 m³, ha^?1 for the rill catchment area, or 3·91 t ha^?1. Mean discharge for the thalweg rill and feeder rills, calculated during a storm event, was 31·101s^?1 and 1·171s^?1, respectively. All flows were fully turbulent and supercritical. We emphasize the need for a spatially distributed approach to the study of runoff and erosion at the catchment scale.     

小良试验站三种植被类型地表径流效应的对比研究

本文分析研究了３种植被类型下的地表径流在汇流、洪峰及径流过程上的特征，差异是巨大的。在径流过程上桉树林和裸地的变地剧烈，几乎没有什么调蓄作用，洪峰流量占一次性降水径流量的绝大部分，涨水和退水流量都较小。本文应用灰色系统ＧＭ（２，１）模型，成功地预测了以年和以月为时间尺度的地表径流序列，其预测模型可以用来对这些时间尺度的地表径流进行预报。     

HEIFE戈壁地区近地层大气的湍流结构和输送特征

根据黑河地区地气相互作用实验研究(HEIFE)1988年POP和1990年PIOP实验的观测资料,分析了戈壁地区近地层大气的湍流结构,主要是风速分量和温度方差的相似关系,以及各有关量的功率谱和湍流通量的协谱。1988年POP期间发现的戈壁近地层大气中白天经常出现的水汽由上而下输送等特殊现象,在1990年PIOP中得到进一步的验证。文中分析了有关物理机制,认为这一现象和众所周知的“绿洲效应”是戈壁-绿洲这一地区性中尺度环流影响的两个侧面。     

Numerical Simulation of Regional Short-Range Climate Anomalies

With the high-speed development of numerical weather prediction, since the later 1980’s, the prediction of short-range climate anomalies has attracted worldwide meteorologists’ attention. What the so called short-range re-fers to the time scale from one month to one season or more. In dealing with the problem of short-range climate pre-diction, two points are needed noticing: one is the basic research to explore or investigate the mechanism of variability of the slow varying components which mainly include internal dynamics of extratropics, external forcings and tropical dynamics, and the other is the modeling efforts to simulate the process of the long-term evolution of the signal which include the improvement of model quality, stochastic prediction and the air-sea-coupled model (Miyakoda et al.,1986). Previous researches on the numerical prediction of short-term climate anomalies are mostly concentrated in the analysis of variables with global spatial scale, especially the global general atmospheric circulation analysis.As to the simulation or prediction of regional short-term climate anomalies, there exist many difficulties and problems. Though some meteorologists are devoting themself to this field, up to now, they have not reached satisfac-tory results. As a primary effort, by using the 2-level general atmospheric circulation model developed in the Institute of Atmospheric Physics, Chinese Academy of Sciences (IAP-AGCM) (Zeng et al., 1989), and taking the year of 1985 as a case, a numerical simulation of regional short-term climate change is completed. We pay high attention to the predictand of anomalous summer rainfall in the Yangtze River and Yellow River valleys, especially its month-to-month variation.     

跃变型扩散的实验研究

本文为一次沿海岸边翻越二维山丘的扩散实验.结果表明:在一定条件下,假若两层空气的湍流强度和尺度的比值不大,当烟羽从上层侵入到下层较强混合气层时,不一定产生燻烟型扩散,仅表现为扩散参数在一定水平距离上的跃变.本文同时介绍了两组风洞实验的结果,其目的在于说明扩散参数跃变存在的事实.     

中国东部近百年的雨量变化

本文用279个气象测站的年雨量资料得到中国东部(100°E以东)1891—1988年大范围平均雨量资料序列.对代表性进行了检验表明:序列在1921年以后能较好地反映大范围气候旱涝状况,而1920年以前则代表性较差.从雨量变化看中国东部的气候在近百年期间是干湿交替出现的,可以分成六个时段.在近四五十年中雨量有减少的趋势,前期雨量偏多,后期从60年代中期以来雨量持续偏少.而且这种变化与北半球副热带其他地区有同相变化的关系.在50年代以前副热带地区雨量的变化却没有明显的同相关系.     

论保持地球上某特定曲线等长的等角投影

本文着重讨论了保持地球上某一条特定曲线等长的等角投影的存在性特点和数学模型,并在此基础上首次求出了保持等角航线等长的等角投影和斜椭圆柱等角投影。本文所述的理论和方法可做为建立等角空间投影的基础。     

地形影响地面运动的观测研究

本文利用矿山爆破,进行了地形对地面运动影响的观测研究.9次爆破的结果表明,山顶处位移和速度的谱曲线的峰区较山前和其它测点的集中,振幅的量值也大,其放大倍率约为3,其中与山体走向平行的水平分量放大得最大,与之垂直的次之,而垂直于地面的最小;山顶测点不同分量上最大位移所对应的周期接近,其对山前的放大量值近于2,也是水平分量大于垂直分量;山顶处地面运动的延续时间取决于爆破的药量和方式,山前等测点延时的放大为3-4倍,也是水平分量大于垂直分量.山顶上地面运动的这种特殊性,是由于入射波所激发的山体共振所引起的.     

利用长周期面波研究华北地区地壳与上地幔结构的横向非均匀性

本文以太行山为界将华北地区分为东西两部分,东部为河淮块体,西部为鄂尔多斯块体.利用最小二乘法,从混合路径基阶瑞利面波群速度频散提取两块体的纯路径频散,并反演其地壳、上地幔的层状结构.所得结表果明,两块体的面波频散和地壳、上地幔结构存在明显差异.东部的河淮块体地壳较薄,地壳内平均速度比西部的鄂尔多斯块体壳内平均速度约低0.13km/s,壳内20km深度左右出现低速层;而西部的块体壳内速度成层递增,未见低速层出现.两块体上地幔顶部速度均偏低,地幔低速层的埋藏深度基本相同.但西部块体地幔低速层厚,且比东部块体地幔低速层的速度约低0.3km/s.     

Surface wave propagation in a transversely isotropic elastic layer overlying a liquid saturated porous solid half-space and lying under the uniform layer of liquid

Dispersion of Rayleigh-type surface wave is studied in a homogeneous transversely isotropic elastic layer overlying a nondissipative liquid-saturated porous solid half-space and lying under a uniform layer of homogeneous liquid. The frequency equation in the form of ninth-order determinant is obtained.Special cases have been deduced by reducing the depth of the layers to zero and by changing the transverse isotropic layer to an isotropic layer. Dispersion curves for the phase velocity have been plotted for a particular model.