四川盆地西部两次暖区暴雨过程分析

利用地面、高空观测资料、卫星和多普勒雷达资料、ERA-Interim再分析资料,对2012年8月17日(12·08)和2017年7月16日(17·07)四川盆地西部两次暖区暴雨过程的环境条件、中尺度对流系统、雷达回波特征和动力抬升条件等预报着眼点进行了对比分析。结果表明:两次过程均出现在低层偏南暖湿气流和地面热低压之中,12·08暴雨发生在副高边缘,水汽输送条件更好,对流持续时间更长,17·07暴雨发生在高空低涡切变后部,高层冷平流使得位势不稳定更强,对流强度更剧烈;12·08暴雨中尺度对流系统沿副高外围自南向北缓慢移动,具有明显列车效应,其强回波质心高度较低,属于积状云为主的混合性降水,17·07暴雨中尺度对流系统在高空低涡后部偏北气流引导下自北向南快速移动,其强回波质心高度较高,属于积状云降水;地面辐合线为对流的发生发展提供了较好的动力触发条件,两次过程强降水均随着地面辐合线的生成而发生,且强降水中心出现在中尺度辐合线附近,并随着辐合线而移动。     

General-altitude transformations between geocentric and geodetic coordinates

Formulas for the general-altitude (height above the ellipsoid) transformation from geocentric to geodetic coordinates and vice versa are derived. The set of four formulas is expressed in each of two useful forms: series expansions in powers of the Earth's flattening and series expansions in powers of the Earth's eccentricity. The error incurred in these expansions is of the order of one part in 3×10⁷.     

A Possible Periodicity in the Radio Light Curves of 3C 454.3

During the period 1966.5–2006.2 the 15GHz and 8GHz light curves of 3C 454.3 (z = 0.859) show a quasi-periodicity of ～12.8 yr (～6.9 yr in the rest frame of the source) with a double-bump structure. This periodic behaviour is interpreted in terms of a rotating double-jet model in which the two jets are created from the black holes of a binary system and rotating with the period of the orbital motion. The periodic variations in the radio fluxes of 3C 454.3 are suggested to be mainly due to the lighthouse effects (or the variation in Doppler boosting) of the precessing jets caused by the orbital motion. In addition, variations in the rate of mass accreting onto the black holes may be also involved.     

银河系中球状星团的空间分布和运动轨道

选用银河系中29个累积光谱型为F型的球状星团样本。根据它们的视向速度，绝对自行等参数，归算处理后得出了各样本星团的空间分布和运动速度。并以此作为初始条件，在给定的3种银河系引力势模型中，采用数值积分方法计算出各样本星团的运动轨道。计算结果表明：（1）大部分样本星团都位于银心距5kpc-10kpc的范围内，相对于银心呈球对称分布，它们的速度也呈椭球分布；（2）29个样本星团按其金属度大小和基本性发类，可分属HB和MP两个次系，且样本星团数随金属度[Fe/H]而变化，在[Fe/H]＝－1．6处出现一个峰值；（3）所有样本星团的轨道运动都呈周期性，大都在一个有界而不封闭的周期轨道上运动，其最大银心距大都在40kpc以内。不同的引力势模型对球状星团轨道的具体形态影响不大，在给定的引力势模型下，当某些星团的运动轨道穿越距银心1kpc附近的区域时会出现“混沌”行为。而样本星团的金属度与其轨道形态之间的相关性并不明显；（4）29个样本星团的轨道半长轴、远银心距和方位周期随金属度的变化规律基本相似。轨道偏心率与金属度有关，对于所选的晕族样本星团而言，大约有24％的样本星团的轨道偏心率低于0．4，不同的引力势模型对近银心距、偏心率和参数的不确定度等量影响较小，但是对远银心距、径向周期和方位周期等参数影响较为明显。     

Chemical differences between minerals from mineralizing and barren intrusions from some North American porphyry copper deposits

Major-element analyses (by electron microprobe) and copper contents (by ion-probe) are reported for primary biotite, amphibole, magnetite, pyroxene, ilmenite, sphene and secondary biotite from intrusive rocks from mineralizing and barren stocks. The districts studied include Christmas, Globe-Miami, Sierrita and Tombstone, in Arizona; Bingham and Alta, Utah; Ely, Nevada; and Brenda, British Columbia. Amphiboles from barren rocks are relatively iron-rich and display only minor compositional variation. In contrast, amphiboles from mineralizing rocks span the range from magnesio-hornblende to actinolite, commonly even within one grain. Barren intrusions (type B) that are temporally distinct from mineralizing intrusions, and barren intrusions outside areas of known mineralization have higher Cu contents in their constituent minerals than do mineralizing intrusions. Barren intrusions (type A) that are deep-level temporal equivalents of Cu-bearing porphyritic rocks are depleted in copper. This suggests that copper is abstracted from not only the apical portions of porphyries but from parts of the deeper parent intrusions. The Cu contents of biotites (av. 23 ppm) and magnetites (97 ppm) from barren type B intrusions contrast with those from mineralizing intrusions, with biotites containing 7 ppm Cu and magnetites 3 ppm Cu. Primary amphiboles from all intrusive rock types have low copper contents, typically 2 to 5 ppm. In the continental North American deposits, the amount of copper available by liberation from or non-incorporation into amphibole, biotite and magnetite during magmatic crystallization or the early hydrothermal stage is low, perhaps too low to be the sole source of copper mineralization, unless copper is abstracted from large volumes (∼ 100 km³) of rock. These results contrast with a study of the island-arc porphyry copper at Koloula, Guadalcanal, where it was argued that sufficient copper for mineralization could have been abstracted from relatively small volumes of host rocks that originally contained as much Cu as the contemporaneous barren rock types.     

冰川,积雪及泥石流灾害研究的回顾与设想

文章总结了４０年来中国科学院兰州冻川冻土研究所在冰川,积雪和泥石流灾害研究中取得的重要成果与进展,分析了冰雪和泥石流灾害的形势,提出了灾害研究的主要方向,其中有加强全球变化对灾害形成和发展的影响研究,以及国家经济建设重心西移后,人类活动可能造成的各类灾害的预研究等,最后提出了应采取的一些措施。     

Pumping-induced Well Hydraulics and Groundwater Budget in a Leaky Aquifer System with Vertical Heterogeneity in Aquitard Hydraulic Properties

In groundwater hydrology, aquitard heterogeneity is often less considered compared to aquifers, despite its significant impact on groundwater hydraulics and groundwater resources evaluation. A semi-analytical solution is derived for pumping-induced well hydraulics and groundwater budget with consideration of vertical heterogeneity in aquitard hydraulic conductivity (K) and specific storage (Ss). The proposed new solution is innovative in its partitioning of the aquitard into multiple homogeneous sub-layers to enable consideration of various forms of vertically heterogeneous K or Ss. Two scenarios of analytical investigations are explored: one is the presence of aquitard interlayers with distinct K or Ss values, a common field-scale occurrence; another is an exponentially depth-decaying aquitard Ss, a regional-scale phenomenon supported by statistical analysis. Analytical investigations reveal that a low-K interlayer can significantly increase aquifer drawdown and enhance aquifer/aquitard depletion; a high-Ss interlayer can noticeably reduce aquifer drawdown and increase aquitard depletion. Locations of low-K or high-Ss interlayers also significantly impact well hydraulics and groundwater budget. In the context of an exponentially depth-decaying aquitard Ss, a larger decay exponent can enhance aquifer drawdown. When using current models with a vertically homogeneous aquitard, half the sum of the geometric and harmonic means of exponentially depth-decaying aquitard Ss should be used to calculate aquitard depletion and unconfined aquifer leakage.     

四川盆地中二叠统天然气成藏特征及巨大勘探前景

近年来,在四川盆地中二叠统钻遇孔隙型白云岩储层,获得一批高产井,呈现出良好的勘探前景,但其勘探潜力如何,能否成为四川盆地继安岳气田之后又一个万亿方大气区亟待明晰。通过对烃源岩特征、沉积特征、储集特征以及成藏模式等方面的深入研究认为,中二叠统具备3套优质烃源岩供烃、孔隙型储层发育、封盖条件好的优越成藏条件,发育自生自储型和下生上储型两套成藏组合。中二叠统发育块状孔隙型白云岩储层和孔隙型灰岩岩溶储层,分布面积大,其储集性能和单井测试产量与安岳气田灯影组相当,勘探潜力巨大,是四川盆地下步寻找万亿方大气区的主要层系。     

Critical Evaluation of Scalar Roughness Length Parametrizations Over a Melting Valley Glacier

We present a field investigation over a melting valley glacier on the Tibetan Plateau. In the ablation zone, aerodynamic roughness lengths (z _0M ) vary on the order of 10⁻⁴–10⁻² m, whose evolution corresponds to three melt phases with distinct surface cover and moisture exchange: snow (sublimation/evaporation), bare ice (deposition/condensation), and ice hummocks (sublimation/evaporation). Bowen-ratio similarity is validated in the stably stratified katabatic winds, which suggests a useful means for data quality check. A roughness sublayer is regarded as irrelevant to the present ablation season, because selected characteristics of scalar turbulence over smooth snow are quite similar to those over hummocky ice. We evaluate three parametrizations of the scalar roughness lengths (z _0T for temperature and z _0q for humidity), viz. key factors for the accurate estimation of sensible heat and latent heat fluxes using the bulk aerodynamic method. The first approach is based on surface-renewal models and has been widely applied in glaciated areas; the second has never received application over an ice/snow surface, despite its validity in (semi-)arid regions; the third, a derivative of the first, is proposed for use specifically over rough ice defined as z _0M > 10⁻³ m or so. This empirical z _0M threshold value is deemed of general relevance to glaciated areas (e.g. ice sheet/cap and valley/outlet glaciers), above which the first approach gives notably underestimated z _0T,q . The first and the third approaches tend to underestimate and overestimate turbulent heat/moisture exchange, respectively, frequently leading to relative errors higher than 30%. Comparatively, the second approach produces fairly low errors in energy flux estimates both in individual melt phases and over the whole ablation season; it thus emerges as a practically useful choice to parametrize z _0T,q in glaciated areas. Moreover, we find all three candidate parametrizations unable to predict diurnal variations in the excess resistances to humidity transfer, thus encouraging more efforts for improvement.