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941.
甘肃天水地区45a来强降水与洪涝灾害特征分析 总被引:9,自引:4,他引:5
洪涝灾害是一种常见的自然灾害,对农业生产和人民生活有极大的影响.通过对甘肃天水地区强降水和洪涝灾害事件资料的整理,对其强降水事件、洪涝灾害变化特征以及二者间地联系进行了分析研究.现有资料统计显示,天水地区没出现过整个区域性洪涝灾害,以局地洪涝灾害为主,强降水事件和洪涝灾害具有显著的年代际和季节性变化特征.由于当地的土地蓄水性能很差,一般性的强降水就可能会产生洪涝灾害.随着气候变暖,这一地区的强降水事件和洪涝灾害呈增加趋势,建议当前应加强对局地强降水事件的防范工作. 相似文献
942.
张腾飞 《热带气象学报(英文版)》2006,12(2):165-173
By using regular meteorological data, physical quantity fields, satellite pictures and Doppler radar
echo data, we analyze the mesoscale features and the conditions of 4 successive heavy precipitation processes in
Yunnan aroused by the storm over the Bay in the early summer. The results show that the life of the storm over
the Bay is usual 2 or 3 days and the cloud top temperature of the storm is always below -65°C. The storm over
the Bay affects Yunnan by mesoscale convective cloud clusters, cloud system in peripheral or weaken itself
moving to the northeast. The Tibetan Plateau shear lines and vortexes, NE-SW convergence channels and
southwest wind convergence supply favorable circulation background and dynamical conditions. There are many
common features about Doppler radar echoes, the flocculent echoes with intensity about 35-45 dBZ move to the
east to produce successive precipitation in Yunnan, and the mesoscale features of southwest jet and wind veering
with altitude not only are favorable to transport warm and moist airflow brought to the north by the storm over
the Bay, but also are favorable to convective development. 相似文献
943.
944.
盆地流体中有机组分的成矿效应 总被引:12,自引:0,他引:12
盆地流体含有丰富的有机组分。有机质-金属耦合作用是盆地流体金属成矿机制的关键,具有极其重要的意义。有机质的成矿作用主要表现为:1)沉积有机质对盆地流体物理化学特征的制约;2)有机组分对金,属成矿元素在盆地流体中的迁移能力、迁移形式以及沉淀就位机制的制约;3)富有机质的地层作为地球化学还原障和H2S障对于流体中金属沉淀就位的制约;4)沉积有机质的演化对于盆地流体运移的制约(通过油气的阵发性析出和二次孔隙的产生)。 相似文献
945.
Experimental Study of Gold and Platinum Solubility in a Complex Fluid under Hydrothermal Conditions 总被引:2,自引:0,他引:2
Abstract: The solubility of gold was studied in water and aqueous NaCl (1– 5 m) solutions under oxygen and sulfur buffered conditions between 300–500C at a constant pressure 1 kb. Two buffer assemblages HMP and PPM were used. Analysis of the scatter in measured values in log mAu–mNaCl–T frame fixed linear dependence between log mAu and T at any studied iso‐pleth (mNaCl) in the form of log mAu = a. T(C) + b. Coefficients of the equation were calculated for water and NaCl (1, 3, 5 m) solutions. The maximum solubility characterizes the NaCl‐free system in the presence of HMP. In the case, Au solubility increases from (log mAu) –6. 72 to –5. 04 at 300 and 500C, respectively. In the presence of PPM, maximum of Au solubility was obtained for the 5 mNaCl solution. In a similar manner solubility rises from –6. 54 to –5. 77 at 300 and 500C, accordingly. In studied fO2/fS2 area the behavior of Au solubility testified that: (i) – a composite interaction between chloride and hydrosulfide speciation of gold affects its total solubility; (ii) – in addition of NaCl up to about 1. 5 m the solubility decreases, more pronounced in the presence of HMP; (iii) – the contribution of chloride in total Au solubility is more for PPM despite of lower fO2value, than for HMP. The solubility of platinum was studied in the Pt–Cl–S–H2O system between 300 and 500C, 1 kb. PPM solid buffer controlled oxidation state, pH and sulfur activity of solutions (H2O, 1 mNaCl and 0. 1 mHCl). Under the conditions, PtS precipitated from the solutions with increasing temperature and acidity. The PtS solubility in the 0. 1 mHCl solutions lowers slightly in the range of 300–500C from –5. 30 to –5. 60 (in log mPt) that is typical to the hydrosulfide species. It was deduced that reducing media, regulated by the PPM assemblage, suppress activity of chloride species of Pt. More oxidizing conditions were modeled in runs using mixtures of Mn(II), Mn(III) and Mn(IV) oxides to buffer the aqueous‐chloride solutions between 300 and 500C, 1 kb. It was found that MnO tends to oxidize at T below 400C forming intermediate Mn‐hydroxides (β–MnOOH, Mn (OH)2 and Mn2(OH)3Cl). These phases are metastable and transfer to Mn3O4 with increasing duration. Generation of the Mn‐hydroxides leads to a change of physical‐chemical parameters of the solutions, such as water activity, pH and Eh. The last results in abrupt increase in the noble metals dissolution. At stable existence of only Mn3O4, the solubility of both Pt and Au lowers to equilibrium values. Essential catalysis effect of Pt on intensity and rate of Mn(II) oxidation was found. The dominant role of chloride of Pt and Au was defined under most oxidized conditions, specified by Mn2O3–MnO2 buffer. So at 400C, dissolved Au (log mAu) increases from –4. 40 in water to –1. 00 in 0. 1 mHCl, and ones of Pt (log mPt) from –4. 80 to –2. 90 accordingly. Thus, mixing of hydrosulfide and chloride solutions, as well as transformation of the systems to the stable state act upon total solubility of the noble metals. 相似文献
946.
Since 1980 when F. Lippmann's seminal paper appeared, ourunderstanding of solubility equilibria involving ionic solidsolutions has been advanced by theoretical considerations as wellas careful experimental studies designed to determine excess Gibbsfunctions. A unified theory of solid-solution aqueous-solutionequilibria as well as the thermodynamic background of thephenomenon of ``stoichiometric saturation' are reviewed.It is shown that Lippmann diagrams effectively summarize thethermodynamic basis of solid-solute aqueous-solution equilibria ofsparingly soluble metal carbonate systems. Clearly, the predictivepower of these diagrams may be limited due to kineticrestrictions. Only when dissolution and precipitation areessentially reversible, favourable conditions to synthesizehomogeneous solid phases can be derived from studies of equilibria. 相似文献
947.
948.
一次连续性大暴雨成因及雷达回波特征分析 总被引:2,自引:0,他引:2
对1998年6月中旬发生在福建省北部地区的连续性大暴雨过程环流特征、影响系统、特殊地形条件作用,中尺度回波系统活动及小尺度强核回波对降水强度的贡献进行了综合分析,力求从雷达回波演变特征找出规律,以提高其短时预报能力。 相似文献
949.
The nature of secondary geochemical dispersion of As, Sb, Hg and Bi in soil and ground water of the semi-arid, tropical, Archaean, auriferous, Hutti-Maski greenstone belt has been investigated for identification of appropriate geochemical techniques for Au exploration in similar terrains.Results indicate that the <180 μm size-fraction of C-horizon soil is an appropriate sampling medium for delineating pedogeochemical anomalies of As, Sb, Hg and Bi related to gold mineralisation. These pedogeochemical anomalies along with anomalous values of alkalinity, chloride, sulphate, As and Sb in groundwater are controlled significantly by primary mineralisation located along shear zones in the greenstone belt. Arsenic anomalies in soil are broad, whereas, those of Sb and Bi are restricted to narrow zones directly over mineralised areas. In contrast, Hg anomalies around known mineralised areas are irregular and do not clearly demarcate the mineralised areas. The study indicates that anomalies of As, Sb and Hg in soil are principally hydromorphic, whereas those of Bi are clastic.The study recommends use of groundwater sampling at 2–3 km spacing with routine analysis of chloride, sulphate and alkalinity along with As and Sb in the first phase. This may be followed up with sampling of C-horizon of soils on a 1 km square grid for As-anomalies. Arsenic-anomalous areas may be sampled for As, Sb, Hg and Bi on a 500 m square grid for detailed exploration. 相似文献
950.