共查询到20条相似文献，搜索用时 0 毫秒
1.
L. L. Kitchatinov 《Astronomy Reports》2004,48(2):153-160
Although the theory of differential rotation is in satisfactory agreement with helioseismological data for the deep convection zone, there are considerable discrepancies near the solar surface. This disagreement can be eliminated if the anisotropy of turbulent convection is taken into account together with the effects of nonuniformity of the medium, on which the most recent models for differential rotation are based. The model for the differential rotation of the convection envelope is supplemented by computations for the transition layer between nonuniform and rigid-body rotation in the upper layers of the solar radiative zone. These are the first computations of differential rotation for the entire volume of the Sun. 相似文献
2.
Abstractthe effect of the large-scale magnetic fields generated by the solar dynamo on the radiation flux issuing from the convection zone is studied. A governing equation describing convective heat transfer is obtained in the framework of mean-field magnetohydrodynamics, with account for the influence of magnetic fields and differential rotation on the energy budget of the convection zone. The principal effects are illustrated using a one-dimensional numerical model. Calculations indicate that the influence of large-scale magnetic fields can modulate the solar irradiance with a relative amplitude of ～0.07%. 相似文献
3.
4.
L. F. Muratov Dr. 《GeoJournal》1991,23(3):207-214
The mathematical model of Raleigh convection on the rotating Earth in deepwater ocean depression is generalized for the case including the meridional temperature gradient. A steadystate thermal shear flow, in the origin of convective instability induced by this gradient has an effect contrary to the stabilizing influence of the Earth rotation. The stability of this flow has been studied with respect to the three-dimensional disturbances. Critical parameters determining the convection are calculated for the Kuril-Kamchatka and Japan trenches. The velocity components of tidal flow have been calculated using the hypothesis of Prandtl mixing way for bottom layer of trenches and the dynamic Richardson number has been calculated. It was noted that dynamic stability condition in bottom layers of the Kuril-Kamchatka and Japan trenches vary within tidal cycle. The periodical component for harmonics O1 and M2 has been calculated. 相似文献
5.
The mean depth of the mantle transition zone depends on the global mantle temperature through the Clapeyron slope. Numerical models of mantle convection with endothermic phase change at 670 km are characterized by quiet periods of partial layering alternating with catastrophic events. During an avalanche, global thermal anomalies, reaching several tens of degrees, and lasting several tens of million years occur that induce a global deepening of the mantle transition zone. The resulting inertia tensor perturbations lead to acceleration of the Earth’s rotation. The bottom heat fluxes remains strong as a consequence of the steep thermal gradient at the CMB level; whereas it decreases to a low level during quiet periods. The upper surface heat flux displays a more complex behavior due to the re-heating of upper mantle by plumes generated at the transition zone and at the CMB. Following these numerical results, two significantly different regimes of mantle convection may have alternated several times during the Earth’s history. The avalanche periods are also associated with a global increase of plate tectonic activity (ridge accretion and continental break-up) due to an increase of the surface velocity during the avalanche process. This work shows the richness of the behavior in surfaces and bottom heat fluxes that arises from the alternation of quiet periods of partial layering with catastrophic avalanche events. Complexities in the real Earth displays are surprisingly simular to those caused by the consequences of mantle avalanches. 相似文献
6.
Large-scale solar magnetic fields in the latitude range 50° S–50° N are analyzed in detail for a long time interval (1915–1990). We are primarily concerned with the two types of large-scale fields forming the two-and four-sector patterns on the Sun. The rotation parameters of these structures are obtained for all latitudes considered. The contribution of the two-sector structure grows and that of the four-sector structure decreases toward high latitudes. The magnetic field is activated simultaneously over a wide latitude range. Since both magnetic-field systems exhibit quasi-rigid rotation, their current systems must either be concentrated in a narrow latitude range or be situated beneath the convection zone, where rotation is only weakly differential. A period of about three years is manifest in the difference between the rotation periods for the two types of magnetic field. Physically, this may imply that these oscillations are external with respect to any level, and there is some phase delay due to their propagation from one level to another. We can conclude with a fair degree of certainty that as the activity level rises, the rotation speed decreases, and vice versa. 相似文献
7.
Small-scale heterogeneity in the deep mantle is concentrated in the upper-mantle transi-tion zone(TZ),in the depth range 410-660 km and also at the bottom 250 km D region.This encour-ages a more detailed investigation of the potential for seismic reflectivity imaging by modelling hetero-geneous structures in mantle convection models including phase transitions of the TZ and D regions.We applied finite elements with variable spacing near the boundary layers in 2-D cylindrical geometry that allow for sufficie... 相似文献
8.
V. N. Krivodubskii 《Astronomy Reports》2001,45(9):738-745
A mixing-length approximation is used to calculate Kλ for a Parker dynamo wave excited by the dynamo mechanism near the base of the solar convection zone (K is the wave number of the dynamo wave and λ the extent of the dynamo region). In a turbulent-dynamo model, this number characterizes the modes of the global magnetic field generated by a mechanism based on the joint action of the mean helical turbulence and solar differential rotation. Estimates are obtained for the helicity and radial angular-velocity gradient using the most recent helioseismological measurements at the growth phase of solar cycle 23. These estimates indicate that the dynamo mechanism most efficiently excites the fundamental antisymmetric (odd), dipole, mode of the poloidal field (Kλ≈?7) at low latitudes, while the conditions at latitudes above 50° are more favorable for the excitation of the lowest symmetric (even), quadrupole, mode (Kλ≈+8). The resulting north-south asymmetry of the poloidal field can explain the magnetic anomaly (“monopole” structure) of the polar fields observed near solar-cycle maxima. The effect of α quenching increases the calculated period of the dynamo-wave propagation from middle latitudes to the equator to about seven years, in rough agreement with the observed duration of the solar cycle. 相似文献
9.
The sector structure and variations in the large-scale magnetic field of the Sun are studied in detail using solar magnetic-field data taken over a long time interval (1915–1990). The two-sector and four-sector structures are independent entities (i.e., their cross correlation is very small), and they are manifest in different ways during the main phases of the 11-year cycle. The contribution of the two-sector structure increases toward the cycle minimum, whereas that of the four-sector structure is larger near the maximum. The magnetic-field sources determining the two-sector structure are localized near the bottom of the convection zone. The well-known 2–3-year quasi-periodic oscillations are primarily associated with the four-sector structure. The variations in the rotational characteristics of these structures have a period of 55–60 years. The results obtained are compared with the latest helioseismology data. 相似文献
10.
L. L. Kitchatinov 《Astronomy Reports》2006,50(6):512-516
Global meridional flows in stars transport angular momentum, thus giving rise to nonuniform rotation. The pattern of differential rotation associated with slow meridional circulation depends on the direction of this circulation. A flow directed from the poles to the equator at the surface and from the equator to the poles in deep layers results in relatively fast rotation of the equatorial zone. If the circulation is directed oppositely, the angular velocity increases from the equator to the poles. Relatively fast rotation at the poles may also result from fast circulation, irrespective of its direction. A simple illustrative explanation is given here to these results. Analytical estimates are supported by numerical calculations. The time variations in the meridional flow observed on the Sun should contribute to torsional oscillations. 相似文献
11.
黄桷湾危岩高边坡是泥岩和砂岩呈类似夹心饼干状软硬互层结构、缓倾坡内的岩质高切坡。危岩高边坡除坡顶的陡崖处厚层砂岩发生崩塌失稳外,主斜坡体下部还存在局部的切层失稳。为确保高边坡下部的工程建设的顺利开展和居民的安全,采用数值模拟的方法对高边坡的主斜坡进行稳定性评价,选取天然自重和地震动荷载两种工况进行分析。计算结果表明:(1)主斜坡岩体在两种工况下仍处于稳定状态,但在地震动荷载作用下稳定系数下降显著; (2)陡崖和主斜坡接触带附近及主斜坡坡脚处应力集中现象明显,发生破坏的可能性更大; (3)主斜坡潜在滑移面位于坡内中深部,剪出口位置可能位于主斜坡的坡脚处。 相似文献
12.
WANG Qian WANG Shi-yu HU Yan-fei College of GeoExploration Science Technology Jilin University Changchun China 《吉林大学学报(地球科学版)》2006,(Z2)
利用MT资料研究位于佳木斯地块和兴凯地块之间过渡地带的岩石圈结构特征。由资料处理所得到的2D反演结果分析出过渡带(属于完达山地体)的地电特征:上部地壳的地电参数在横向上变化较大,中下部地壳所存在的低阻层带可延伸至兴凯地块岩石圈地幔之中,是否在更深位置延伸至佳木斯地块岩石圈地幔还不能确定。两古老地块的高阻特征存在一定的差异,即佳木斯地块的阻值明显高于兴凯地块。即完达山地体的南部作为两古老地块之间的过渡带,可能发生过古大洋洋中脊软流圈物质的垂向对流(上涌),并发生岩石圈板片向两古地块的俯冲过程。 相似文献
13.
地球内核快速旋转的发现与全球变化的轨道效应 总被引：3，自引：0，他引：3
科里奥利效应是产生内核快速旋转的主要原因。科氏力使上升物质向西漂移，下降物质向东漂移；造成地球外层自转减速，地球内层自转加速。所以，自旋体中的垂直运动可以产生大规模的水平运动——圈层差异旋转。地震波测量结果表明，内核旋转速度每年比地壳地幔快１°。对于一个内核差异旋转的地球，太阳辐射不仅形成地磁场的内外磁尾和地壳与内核的反向振动，而且影响核幔角动量交换和电磁耦合，从而控制了地球内能的释放，形成天文周期与地质旋回的一一对应关系。地球轨道和太阳轨道的全球变化响应，为太阳辐射量变化控制地球内能释放提供了证据 相似文献
14.
T Hughes 《Tectonophysics》1973,18(3-4)
Crustal tensile, compressive, and shear fracture zones seem to correlate with a crust deformed in torsion due to Coriolis force perturbations of a mantle convection pattern having polar symmetry. A crudely tetrahedral arrangement of four convection cells seems to provide this pattern. A detailed examination of the hypothesis apparently requires that converging mantle convection flow be confined to the zone of low seismic velocities, where partial melting occurs. Convection flow in this zone is confined to molten grain fillets, resulting in a high convection velocity in the liquid phase.The Coriolis force laterally deflects the converging convection flow, which presses against the fillet walls like water against turbine blades. This causes the solid grain matrix to deform in torsion. The major weakness of the model is that it cannot reconcile isostatic uplift viscosities in the partly molten zone with observed viscosities for metals and oxides at or near their pressure melting points. This reconciliation is a general problem which all tectonic models must face. 相似文献
15.
Turbidity currents descending the slopes of deep‐water extensional basins or passive continental margins commonly encounter normal‐fault escarpments, but such large‐magnitude phenomena are hydraulically difficult to replicate at small scale in the laboratory. This study uses advanced computational fluid dynamics numerical simulations to monitor the response of large, natural‐scale unconfined turbidity currents (100 m thick and 2000 m wide at the inlet gate) to normal‐fault topography with a maximum relief of nearly 300 m. For comparative purposes, the turbidity current is first released on a non‐faulted pristine slope of 1·5° (simulation model 1). The expanding and waxing flow bypasses the slope without recognizable deposition within the visibility limit of 8 vol.% sand grain packing. Similar flow is then released towards the tip (model 2) and towards the centre (model 3) of a normal‐fault escarpment. In both of these latter models, the sand carried by flow tends to be entrapped in four distinct depozones: an upslope near‐gate zone of flow abrupt expansion and self‐regulation; a flow‐transverse zone at the fault footwall edge; a flow‐transverse zone at the immediate hangingwall; and a similar transverse zone near the crest of the hangingwall counter‐slope, where some of the deposited sand also tends to be reshuffled to the previous zone by a secondary reverse underflow. The near‐bottom reverse flow appears to be generated on a counter‐slope of 1·1°, increased to 2·0° by deposition. The Kelvin–Helmholtz interface instability plays an important role by causing three‐dimensional fluctuations in the flow velocity magnitude and sediment concentration. The thick deposits of large single‐surge flows may thus show hydraulic fluctuations resembling those widely ascribed to hyperpycnal flows. The study indicates further that the turbiditic slope fans formed on such fault topographies are likely to be patchy and hence may differ considerably from the existing slope‐fan conceptual models when it comes to the spatial prediction of main sand depozones. 相似文献
16.
V. V. Pipin 《Astronomy Reports》2007,51(5):411-420
We consider a solar dynamo mechanism that generates large-scale magnetic fields due to the combined action of cyclonic flows (the α effect), differential rotation (the Θ effect), and the non-uniformity of large-scale magnetic fields (the Θ × J effect). Our results are based on numerical model which takes into account currently available data on the differential rotation of the convection zone and the intensity of convective flows in the solar interior. A reasonable choice of parameters characterizing the intensity of magnetic-field generation by the α and Θ × J mechanisms can account for an oscillatory dynamo regime with properties similar to the 22-year magnetic-activity cycle of the Sun. We analyze the nonlinear saturation of the generation effects in the large-scale magnetic field, due to either magnetic stresses or the conservation of magnetic helicity. Allowance for the helicity of the small-scale magnetic fields is of crucial importance in limiting the energy of the generated large-scale magnetic field. 相似文献
17.
冀北滦平盆地大北沟组叶肢介生物地层特征
与大北沟阶单位层型的建立 总被引：5，自引：4，他引：1
滦平县火斗山乡张家沟榆树下村大北沟组（1棚剖面地层连续,顶底清楚,化石丰富,以沉积岩为主夹少量火山岩,可分为3个岩性段。1段含孢粉化石;2至3段化石极为丰富,有叶肢介、昆虫、介形类、双壳、腹足类、鲎虫、鱼、植物等化石。其中叶肢介化石自大北沟组近底部一直分布于顶部,可见至少25个化石层．计5科9属36种,统属于尼斯托叶肢介群（Nestoria Fauna）。自下而上又可进一步划分为3个叶肢介化石带。以最底部化石带中Mstoriapissovi,Jibeilimnadia ovata的首现为标志,即为大北沟阶的开始,榆树下剖面可作为大北沟阶理想的单位层型剖面。根据化石组合、地层层序、区域地层对比及同位素年代资料,大北沟阶的时代应为晚侏罗世,可能更近于晚侏罗世晚期。文中描述了一些叶肢介属种。 相似文献
18.
黄河三角洲滨海区沉积物的分异特征与规律 总被引：7，自引：0，他引：7
根据2000年79月黄河三角洲滨海区表层沉积物的分析结果,运用F lem ing的三角图式对沉积环境进行划分,并在此基础上结合沉积物结构、地形和水动力条件,探讨了沉积物的分布规律及其作用机制。结果表明:研究区域可划分为废弃三角洲滨海区、现行河口区和莱州湾滨海区三个沉积环境。对于废弃三角洲沉积区,在早期废弃的湾湾沟海区风浪作用为主,沉积物普遍较粗,抗冲能力较强;废弃不久的飞雁滩海区在波流联合作用下,沉积物粒径由岸向海变细,大致在-5-6m水深处存在一明显的界限,该水深以浅砂含量较高;而该水深以深以粉砂和粘土为主,砂含量较低。现行河口区,由于沙嘴前方强潮流带的作用,沉积物粒径由岸向海表现为粗—细—粗的演变趋势。在莱州湾海区,由于潮流场的影响,以广利河河口为界,以北粒径较细,而以南则较粗。 相似文献
19.
This study investigates the mechanism of formation of convection plumes of mushroom shape in sub-solidus mantle and their prediction.The seismic-tomographic images of columnar structures of several hundreds kilometers in diameter have been reported by several researchers,while the much cherished mushroom-shaped plume heads could only be found in computational geodynamics(CGD) models and simple small-scale laboratory analogue simulations.Our theory of transient instability shows that the formation of conv... 相似文献
20.
H.C. Hardee 《Tectonophysics》1982,84(2-4)
Thermal convection above large shallow magma bodies in the crust is treated as a one-dimensional bottom-heated convection process in permeable media. Solutions for single-phase convection are briefly reviewed and a solution is developed for two-phase permeable convection in bottom-heated media. Heat flow measurement techniques are discussed for permeable geologic zones above magma bodies and these techniques give consistent results for solidifying lava lakes in Hawaii (Kilauea Iki, q=257 W/m2) and Iceland (Heimaey, q = 465 W/m2).The heat loss from a magma body is a strong function of the permeability when a two-phase convection zone occurs above the magma body, and the heat loss is independent of the thickness of the two-phase convection zone. In steady-state two-phase convection zones, where permeability does not vary appreciably with depth, convective heat flow restrictions tend to limit the maximum saturation temperatures at depth to around 250°C—an effect observed in many geothermal steam fields. A conduction-dominated transition zone tends to occur between the two-phase zone and the magma body and the thickness of this transition zone may easily range from a few meters to several kilometers, depending on the permeability. 相似文献