甘肃西和县大桥金矿床的成因研究

大桥金矿床位于岷县北-宕昌北大断裂与窑上-石峡大断裂之间.金矿化严格受三叠系下部建造层下岩性段(Ta-1)硅质角砾岩的控制.硅质角砾岩呈层状产出,层位稳定.矿石为有机质含量高并具有黄铁矿化的硅质角砾岩,其黄铁矿环带发育.硅质角砾岩和纹层状硅质岩在稀土元素配分图上未表现出热水沉积的特征,其Fe/Ti-Al/(Al+ Fe...     

Impact of the central Pacific zonal wind divergence and convergence on the central Pacific El Nio event

The central Pacific(CP) zonal wind divergence and convergence indices are defined, and the forming mechanism of CP El Nio(La Nia) events is discussed preliminarily. The results show that the divergence and convergence of the zonal wind anomaly(ZWA) are the key process in the forming of CP El Nio(La Nia) events. A correlation analysis between the central Pacific zonal wind divergence and convergence indices and central Pacific El Nio indices indicates that there is a remarkable lag correlation between them. The central Pacific zonal wind divergence and convergence indices can be used to predict the CP events. Based on these results, a linear regression equation is obtained to predict the CP El Nio(La Nia) events 5 months ahead.     

Linear and weakly nonlinear internal wave theories applied to “morning glory” waves

Abstract

Detailed comparisons are made between the predictions of Benjamin's weakly nonlinear theory for internal solitary waves in fluids of great depth, with observational data on solitary wave-type disturbances in the lower atmosphere associated with the “morning glory” phenomenon.

It is shown that, while the theory is not wholly unreasonable, neither is it completely satisfactory. In particular, although the calculated wave speeds are generally close to those observed, they are no improvement on those based on linear long wave theory; at the same time the predicted wave half-widths are too large by a factor of two to three. The limitations of the theory appear to be associated with the requirement that wave half-widths are much less than the total fluid depth, a condition not satisfied in the atmospheric case. However, the alternative theory for shallow fluids, based on the Korteweg-de Vries equation is found to be even more unsuitable.

Our analyses highlight some of the problems in comparing theory with observations and bring to the fore some of the present limitations of the data for such purposes.     

基于扩展有限元的深部岩体分区破裂化现象初步数值模拟

通过轮廓法追踪岩石裂纹扩展轨迹,将其嵌入ABAQUS扩展有限元（EFE）平台,对单轴压力下裂隙试件受压过程进行了模拟验证,裂纹起裂扩展效果良好。以此为平台,将推导得到的弧形裂纹应力强度因子嵌入其中,以最大周向拉应力准则为开裂准则,认为当其大于岩体断裂韧度时,硐室围岩体内初始裂纹将开始扩展。在此基础上,以发现分区破裂现象的圆形隧道模型试验为背景开展了分区破裂的数值模拟试验。模拟结果发现,深部巷道围岩出现了3~4层破裂分区,证实深部巷道围岩存在分区破裂现象。将数值模拟结果与模型试验完成后模型围岩破坏状态对比,发现二者破裂区分布特征基本一致。数值模拟结果表明,EFEM方法在处理复杂岩体裂纹问题方面的有效性。     

考虑卸荷效应的深埋隧洞围岩分区破坏数值模拟

基于卸荷岩体力学基本理论,运用三维有限差分软件,提出以塑性体积应变增量变化区间与不同卸荷区域岩体力学参数相对应的卸荷模拟方法,模拟了不同侧压系数条件下开挖洞周附近围岩最大体积应变增量以及围岩损伤范围的变化情况。数值模拟结果表明：当侧压系数较低时,洞周附近围岩的塑性体积应变增量区域的外边界近似为竖向椭圆形,随着侧压系数的增大,其外边界逐渐向圆形变化,最后变为横向椭圆形。侧压系数越大,围岩的卸载效应越显著,洞周附近围岩的塑性体积应变增量就越大,其所产生的围岩损伤范围也相应越大。利用所获得的结果,可以为深埋隧洞的稳定性分析以及支护设计提供依据。     

基于颗粒-界面-基体模型圆形巷道围岩中应力与应变演变分析

视岩石将由3种成分构成：颗粒、界面和基体,采用FLAC模拟圆形巷道开挖之后围岩中的剪切应变增量、最小及最大主应力的分布及演变规律。在静水压力条件下,剪切应变增量的高值区主要分布在软弱的基体之中,形成了相互交织的剪切带网格,而最小主应力的高值区（环向高受压区）主要分布在相互接触的颗粒之中,形成了若干圆环。当侧压系数不等于1时,剪切带网格的轮廓呈三角形。颗粒尺寸的增加使剪切带的数目降低,长度增加,最小主应力的高值区的数目降低,间距增加;颗粒尺寸大时的结果与分区破裂化现象相近。由此提出一种可能的裂化机制：节理岩体中的若干岩块由于自组织作用而被挤成1圈,如果应力水平足够高,就可以形成多条环向的被未破坏区隔开的破坏区。     

云南东川深沟泥石流分区治理模式初探

通过对东川深沟泥石流特征及其分区治理措施进行详细的调查、分析,探讨了深沟泥石流分区治理模式,以期为我国山区城镇泥石流沟谷的综合治理提供可靠的参考依据。     

Roles of forced and inertially unstable convection development in the onset process of Indian summer monsoon

The NCEP/NCAR R1 reanalysis data are employed to investigate the impact of forced and inertial instability in the lower troposphere over the Arabian Sea on the onset process of Indian summer monsoon(ISM),and to reveal the important role of zonal advection of zonal geostrophic momentum played in the forced unstable convection.Results show that during the ISM onset the zero absolute vorticity contour(??=0)shifts northward due to the strong cross-equatorial pressure gradient in the lower troposphere over southern Arabian Sea.Thus a region with negative absolute vorticity is generated near the equator in the northern hemisphere,manifesting the evident free inertial instability.When a southerly passes through this region,under the influence of friction a lower convergence that facilitates the convection flourishing at the lower latitudes appears to the north of zero absolute vorticity contour.However,owing to such a traditional inertial instability,the convection is confined near the equator which does not have direct influence on the ISM onset.On the contrary in the region to the north of the zero absolute vorticity contour and to the south of the low pressure center near the surface,although the atmosphere there is inertially stable,the lower westerly jet can develop and bring on the apparent zonal advection of zonal geostrophic momentum.Both theoretical study and diagnosing analysis present that such a zonal advection of geostrophic momentum is closely associated with the zonal asymmetric distribution of meridional land-sea thermal contrast,which induces a convergence center near and further north of the westerly jet in the lower troposphere over the southwestern coast of the Indian Peninsula,providing a favorable lower circulation for the ISM onset.It illustrates that the development of convection over the Arabian Sea in late spring and early summer is not only due to the frictional inertial instability but also strongly affected by the zonal asymmetric distribution of land-sea thermal contrast.Moreover,before the ISM onset due to the eastward development of the South Asian High(SAH)in the upper troposphere,high potential vorticity is transported to the region over the Arabian Sea.Then a local trumpet-shaped stream field is generated to cause the evident upper divergence-pumping effect which favors the ISM onset.When the upper divergence is vertically coupled with the lower convergence resulted from the aforementioned forced unstable convection development near the southwestern coast of Indian Peninsula,the atmospheric baroclinic unstable development is stimulated and the ISM onset is triggered.     

高空急流区内纬向基本气流加速与EP通量的关系

采用多时间尺度方法, 并假设纬向基本气流是正压的, 在不引入剩余环流的情况下, 推导出纬向基本气流局地变化与一种新形式Eliassen-Palm通量之间的关系, 这种Eliassen-Palm通量关系在形式上比较简单, 而且物理意义明确, 适合诊断分析高空急流区内纬向基本气流的加速与减速.理论分析表明, 正压纬向基本气流的局地变化由新形式Eliassen-Palm通量散度决定.作者利用该Eliassen-Palm通量关系对2002年12月一次寒潮过程中200 hPa等压面上纬向基本气流的发展演变进行了诊断分析.诊断结果表明, 在200 hPa纬向基本气流急流区内, 新形式Eliassen-Palm通量散度是影响纬向基本气流发展演变的重要因子, 并且纬向基本气流的加速与减速主要是由新形式Eliassen-Palm通量中扰动动量的经向输送造成的.     

纬向切变线暴雨落区的精细化分析

应用常规观测资料、NCEP 1°×1°再分析资料,对纬向切变线的暴雨落区进行精细化分析。结果表明:虽然低层切变线的位置对暴雨落区很重要,但不是判断暴雨落区的唯一依据。影响系统的空间结构及冷暖空气的相互作用对暴雨落区的精细化预报至关重要。当东北地区有冷空气入侵,山东省为一致东北风时,除了与切变线对应的暴雨区,还有因锋面抬升作用造成的地面东北风中的暴雨区;而当东北地区为暖低压,850 hPa冷中心盘踞山东省时,切变线南侧西南暖湿气流强盛,此时暴雨区位于切变线南侧和地面静止锋之间的鲁南地区;风场辐合中心往往和高湿舌对应,高湿舌前部和风场辐合中心附近是暴雨落区。