半干旱草原下垫面能量平衡特征及土壤热通量对能量闭合率的影响   总被引：3，自引：0，他引：3  

岳平  张强  牛生杰  成华  王西育 《气象学报》2012,70(1):136-143

土壤热通量在半干旱草原下垫面能量平衡研究中极为重要,土壤热通量估计不够准确是导致地表能量不平衡的一个重要原因。利用2008年6—9月锡林郭勒草原主生长期地表辐射、通量和土壤温度梯度观测资料,研究中纬度半干旱草原下垫面地表能量平衡特征。首先,在分析能量平衡各分量月平均日变化特征的基础上,通过对土壤热流量板观测的5 cm深度土壤热通量(G)的相位前移,研究了土壤热通量相位滞后对地表能量平衡产生的影响;其次,利用谐波分析方法,通过计算地表土壤热通量(Gs),分析了地表到热流量板之间的土壤热量储存对地表能量平衡的影响。结果表明:(1)将土壤热通量相位前移30 min,湍流通量与可利用能量(Rn-G)线性回归的斜率从0.835增加到0.842,地表能量闭合率提高了0.7%,但仍有15.8%的能量不闭合;(2)考虑了地表到热流量板之间的土壤热量储存之后,湍流通量与可利用能量之间的回归斜率达到0.979,能量不闭合程度仅为2.1%。  相似文献   

中国东部冬季气温异常的主模态与大气环流的关系   总被引：4，自引：3，他引：1  

陈少勇  夏权  白登元  张燕霞 《气象科学》2010,30(1):27-33

利用中国东部季风区375个测站,1961-2006年历年平均地面气温资料,采用EOF、SVD、相关分析等方法,分析了中国东部季风区冬季气温与500hPa高度场异常变化的关系。结果表明:影响冬季气温的关键区有两个,皆为显著正相关;SVD分析表明:乌山脊弱,东亚槽浅,纬向环流偏强,经向环流偏弱,极涡面积偏小,使南下冷空气偏少,冬季气温易偏高。上年7月北大西洋高压异常偏强(偏弱),次年冬季气温将会异常偏暖(偏冷),北大西洋前期高度场与气温普遍有密切的关系,主要影响长江流域及其以北的季风中北部区;建立了气温距平与北大西洋关键区上年7月高度距平的关系,并建立了均生函数模型,预测了未来20 a的气温变化趋势。  相似文献   

Continental rift evolution: From rift initiation to incipient break-up in the Main Ethiopian Rift, East Africa   总被引：2，自引：0，他引：2  

Giacomo Corti   《Earth》2009,96(1-2):1-53

The Main Ethiopian Rift is a key sector of the East African Rift System that connects the Afar depression, at Red Sea–Gulf of Aden junction, with the Turkana depression and Kenya Rift to the South. It is a magmatic rift that records all the different stages of rift evolution from rift initiation to break-up and incipient oceanic spreading: it is thus an ideal place to analyse the evolution of continental extension, the rupture of lithospheric plates and the dynamics by which distributed continental deformation is progressively focused at oceanic spreading centres.The first tectono-magmatic event related to the Tertiary rifting was the eruption of voluminous flood basalts that apparently occurred in a rather short time interval at around 30 Ma; strong plateau uplift, which resulted in the development of the Ethiopian and Somalian plateaus now surrounding the rift valley, has been suggested to have initiated contemporaneously or shortly after the extensive flood-basalt volcanism, although its exact timing remains controversial. Voluminous volcanism and uplift started prior to the main rifting phases, suggesting a mantle plume influence on the Tertiary deformation in East Africa. Different plume hypothesis have been suggested, with recent models indicating the existence of deep superplume originating at the core-mantle boundary beneath southern Africa, rising in a north–northeastward direction toward eastern Africa, and feeding multiple plume stems in the upper mantle. However, the existence of this whole-mantle feature and its possible connection with Tertiary rifting are highly debated.The main rifting phases started diachronously along the MER in the Mio-Pliocene; rift propagation was not a smooth process but rather a process with punctuated episodes of extension and relative quiescence. Rift location was most probably controlled by the reactivation of a lithospheric-scale pre-Cambrian weakness; the orientation of this weakness (roughly NE–SW) and the Late Pliocene (post 3.2 Ma)-recent extensional stress field generated by relative motion between Nubia and Somalia plates (roughly ESE–WNW) suggest that oblique rifting conditions have controlled rift evolution. However, it is still unclear if these kinematical boundary conditions have remained steady since the initial stages of rifting or the kinematics has changed during the Late Pliocene or at the Pliocene–Pleistocene boundary.Analysis of geological–geophysical data suggests that continental rifting in the MER evolved in two different phases. An early (Mio-Pliocene) continental rifting stage was characterised by displacement along large boundary faults, subsidence of rift depression with local development of deep (up to 5 km) asymmetric basins and diffuse magmatic activity. In this initial phase, magmatism encompassed the whole rift, with volcanic activity affecting the rift depression, the major boundary faults and limited portions of the rift shoulders (off-axis volcanism). Progressive extension led to the second (Pleistocene) rifting stage, characterised by a riftward narrowing of the volcano-tectonic activity. In this phase, the main boundary faults were deactivated and extensional deformation was accommodated by dense swarms of faults (Wonji segments) in the thinned rift depression. The progressive thinning of the continental lithosphere under constant, prolonged oblique rifting conditions controlled this migration of deformation, possibly in tandem with the weakening related to magmatic processes and/or a change in rift kinematics. Owing to the oblique rifting conditions, the fault swarms obliquely cut the rift floor and were characterised by a typical right-stepping arrangement. Ascending magmas were focused by the Wonji segments, with eruption of magmas at surface preferentially occurring along the oblique faults. As soon as the volcano-tectonic activity was localised within Wonji segments, a strong feedback between deformation and magmatism developed: the thinned lithosphere was strongly modified by the extensive magma intrusion and extension was facilitated and accommodated by a combination of magmatic intrusion, dyking and faulting. In these conditions, focused melt intrusion allows the rupture of the thick continental lithosphere and the magmatic segments act as incipient slow-spreading mid-ocean spreading centres sandwiched by continental lithosphere.Overall the above-described evolution of the MER (at least in its northernmost sector) documents a transition from fault-dominated rift morphology in the early stages of extension toward magma-assisted rifting during the final stages of continental break-up. A strong increase in coupling between deformation and magmatism with extension is documented, with magma intrusion and dyking playing a larger role than faulting in strain accommodation as rifting progresses to seafloor spreading.  相似文献   

Quantitative analysis of top-seal capacity: offshore Netherlands,southern North Sea     

Spain  David R.  Conrad  Curtis P. 《Geologie en Mijnbouw》1997,76(3):217-226

Sealing characteristics of the caprock to the Main Buntsandstein reservoir sands in the P blocks in the Dutch offshore are assessed based on a core from the P15 well. The core which represents the Main Buntsandstein, Solling, Röt, and Muschelkalk interval has been analyzed using standard geologic and petrophysical techniques including mercury-injection capillary-pressure tests. The caprock to the Main Buntsandstein reservoir sands consists of anhydritic and/or dolomitic sandstone to argillaceous siltstone, silty shale, and dolostone. Early emplacement of nodular anhydrite followed by cementation and replacement by anhydrite, dolomite, and siderite has resulted in tight, submicroporous pore geometries which act as good to excellent seals. Capillary entry pressures of the best caprock lithologies are such that gas columns of the order of 300 m could potentially be trapped. The actual column height in P15 is about 125 m as indicated by RFT data. The presence of significant gas accumulations in the Main Buntsandstein in the P12, P14, P15, P18 and adjoining Q8 and Q16 blocks suggests that the P15 top-seal quality may be representative for that area.  相似文献   

Structural and metamorphic evolution of the rocks of the Jutogh Group, Chur half-klippe, Himachal Himalayas: A summary and comparison with the Simla area     

Dilip K. Mukhopadhyay  Tamal K. Ghosh  Bidyut K. Bhadra  Deepak C. Srivastava 《Journal of Earth System Science》1997,106(4):197-207

The rocks of the Jutogh Group in the Himachal Himalayas and their equivalents elsewhere are now considered to represent a several km thick crustal scale ductile shear zone, the so called Main Central Thrust Zone. In this article we present a summary of structural and metamorphic evolution of the Jutogh Group of rocks in the Chur half-klippe and compare our results with those of Naha and Ray (1972) who worked in the adjacent Simla klippe. The deformational history of the Jutogh Group of rocks in the area around the Chur-peak, as deduced from small-scale structures, can be segmented into: (1) an early event giving rise to two sets of very tight to isoclinal and coaxial folds with gentle dip of axial planes and easterly or westerly trend of axes, (2) an event of superimposed progressive ductile shearing during which a plethora of small-scale structures have developed which includes successive generations of strongly non-cylindrical folds, several generations of mylonitic foliation, extensional structures and late-stage small-scale thrusts, and (3) a last stage deformation during which a set of open and upright folds developed, but these are regionally unimportant. The structure in the largest scale (tens of km) can be best described in terms of stacked up thin thrust sheets. Km-scale asymmetric recumbent folds with strongly non-cylindrical hinge lines, developed as a consequence of ductile shearing, are present in one of these thrust sheets. The ductile shearing, large-scale folding and thrusting can be related to the development of the Main Central Thrust Zone. The microstructural relations show that the main phase of regional low-to medium-grade metamorphism (T ≈ 430–600°C andP ≈ 4.5–8.5 kbar) is pre-kinematic with respect to the formation of the Main Central Thrust Zone. Growth zoned garnets with typical bell-shaped Mn profiles and compensating bowl-shaped Fe profiles are compatible with this phase of metamorphism. Some of the larger garnet grains, however, show flat compositional profiles; if they represent homogenization of growth zoning, it would be a possible evidence of a relict high-grade metamorphism. The ductile shearing was accompanied by a low-greenschist facies metamorphism during which mainly chlorite and occasionally biotite porphyroblasts crystallized.  相似文献   

Fault mechanisms and tectonic implication of the 1985–1987 earthquake sequence in south-western Ethiopia     

Atalay Ayele  Ronald Arvidsson 《Journal of Seismology》1997,1(4):383-394

Integrated inversions of short-period P, broadband P, and long-period P &s waves are done for fault mechanisms, focal depths, seismic moments, and source-time functions from the largest four earthquakes of the 1985 and 1987 earthquake sequence in south-western Ethiopia. These earthquakes had similar normal-faulting mechanisms. The general trends of the fault planes follow the Main Ethiopian Rift which is in agreement with foreshock-aftershock distribution, surface breaks and geology. Despite the morphological discontinuity of the Main Ethiopian Rift at its southern tip, the mode of deformation of the continental crust under study shows its extension southward. There are no significant strike-slip components trending NW–SE in all the mechanisms which would have been associated with the Aswa Fault Zone in southern Sudan or Anza Rift in northern Kenya. We also infer that the relatively broad fracture zone at the southern extreme of the Main Ethiopian Rift demonstrates the early stage of the break-up between the Nubia and Somalia plates in comparison with the Main Ethiopian Rift proper and the Afar Depression. The main shock of the sequence (M_w = 6.3) ruptured at a depth of 6.8 km, shallower than expected since the depth of earthquakes generally increase southward from the Afar Depression. The shallow depth of earthquake occurrence is supported by surface deformations with an overall trend in the direction of the Main Ethiopian Rift.  相似文献   

FLUVIAL PROCESSES AND SEDIMENT SCOUR RATE OF THE YELLOW RIVER UNDER ACTION OF UNSTEADY FLOWS     

Yong-Nian XU Zhi-Yong LIANG  Thao-Yin WANG China Institute of Water Resources  Hydropower Research  Beijing  China. International Research  Training Center on Erosion  Sedimentation  Beijing  China. 《国际泥沙研究》2001,16(2)

1 wrsoooCTIoxThe Yeuow mver crtes a huge amoun of sedimcht and the noods often cause raPid and severeerosinn and dePOsihon. The channl bed of the YelOw mver often exPeriences degIadation in the mainchannel during fioods. In some cases vigorous erosion uP to l0 meters takes place in a shOrt Period oftiIn. Such phenomenon usually occurs in the ndddie reaChs of the Yelow mver and its tributaries suchas the Wdse mVer the Beiluohe mver etc. For examPle, th6 hyPenconcentraed nood in July l…  相似文献   

渤海、黄海沿岸主要港湾假潮的基本特征   总被引：3，自引：0，他引：3  

李坤平  陈则实 《海洋与湖沼》2002,33(2):128-138

基于港湾假潮振动的基本原理，从渤海、黄海沿岸20个验潮站多年水位自记曲线资料获取假潮参数，并对其做了统计分析，给出了假潮的统计特征，还讨论了假潮形成的初步原因。结果表明，该海域主要港湾假潮出现具有明显的局地性、季节性和年际变化；夏季是大振幅假潮（振幅^1)≥80cm）的多发期，冬季基本上不出现；龙口港湾的大振幅假潮最为突出，最大振幅可达293cm；气压和风速、风向突变的良好配合，是发生大振幅假潮的主要原因。  相似文献   

渔船主机排废气特性的研究     

宋协法  杜坚刚  高明勇  郭书远 《海洋湖沼通报》2001,(3):46-51

通过对东京水产大学研究练习船－神鹰丸主机转速、功率，以及排废气的测定，优化渔船主机操纵主机可以使船舶在各种航行工况下主机NOx的排放率达到最低值。结果表明，当船舶航速为4节时，主机转速应设定在750转／分，此时NOx的排放率最低为10．3g/kWh，比常规操纵减少9％；当船舶航速为8节时，主机转速应设定在750转／分，此时NOx的排放率最低为10．5g/kWh，比常规操纵减少4．6％；当船舶航速为10节时，主机转速应设定在875转／分，此时NOx的排放率最低为11．6g/kWh，比常规操纵减少1．7％；当船舶航速为12节时，主机转速应设定在750转／分，此时NOx的排放率最低为12．5g/kWh，比常规操纵减少6％；当船舶航速为13节时，主机转速应设定在750转／分，此时NOx的排放率最低为12g/kWh，比常规操纵减少3．2％。在拖网作业过程中，船舶航速为4节，主机转速应设定在875转分，此时NOx的拓放率最低为12．3g/kWh，比常规操纵减少2．8％。在延绳钓作业过程中，船舶航速为10节，主机转速应设定在875转／分，此时NOx的排放率最低为11．5g/kWh,比常规操纵减少1．7％。  相似文献   

甘肃省主要河流径流时空分布规律及演变趋势分析   总被引：21，自引：0，他引：21  

胡兴林 《地球科学进展》2000,15(5):516-521

通过对甘肃省主要河流径流时空分布规律的分析研究,得出干旱缺水的主要原因是各河年径流丰水时段很短,一般只有2～3年;枯水时段很长,可达7～26年;祁连山区许多河流多年均值基本稳定。并预测从1998年开始至2009年,全省诸河水量从枯水年代转向平水到偏丰的年代;建议全省必须树立长期抗旱的思想,水资源利用必须进行系统分析优化配置。  相似文献