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81.
Simulation of multigaussian stochastic fields can be made after a Karhunen-Loéve expansion of a given covariance function.
This method is also called simulation by Empirical Orthogonal Functions. The simulations are made by drawing stochastic coefficients
from a random generator. These numbers are multiplied with eigenfunctions and eigenvalues derived from the predefined covariance
model. The number of eigenfunctions necessary to reproduce the stochastic process within a predefined variance error, turns
out to be a cardinal question. Some ordinary analytical covariance functions are used to evaluate how quickly the series of
eigenfunctions can be truncated. This analysis demonstrates extremely quick convergence to 99.5% of total variance for the
2nd order exponential (‘gaussian’) covariance function, while the opposite is true for the 1st order exponential covariance
function. Due to these convergence characteristics, the Karhunen-Loéve method is most suitable for simulating smooth fields
with ‘gaussian’ shaped covariance functions. Practical applications of Karhunen-Loéve simulations can be improved by spatial
interpolation of the eigenfunctions. In this paper, we suggest interpolation by kriging and limits for reproduction of the
predefined covariance functions are evaluated. 相似文献
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In this paper, the process of oasis-desert circulation (ODC) is simulated by MM5V3.5 model through designing an ideal oasis-desert scheme and assuming that initial atmosphere is at rest (V = 0). The findings showed that the key of forming special oasis boundary structure is the difference of energy and water between oasis and desert. The evaporation of oasis surface consumes heat energy, and the low temperature of oasis causes an oasis breeze circulation (OBC), which drives an ODC with a downdraft over the oasis and an updraft over the desert. Later, the cold, dry and stable boundary over oasis is gradually formed, on the contrary,the atmospheric boundary over desert on the edge of oasis is hot, humid and unstable and its height is about 600 hPa. The updraft over the desert forms a wet ring that acts as a vertical wall weakening the low-level moisture exchange between the oasis and desert. The downdraft of OBC increases the atmospheric stability that reduces the oasis evaporation. The low-level outflow from the oasis (into the desert) prevents the dry, hot air flowing from the desert into the oasis.Thus an oasis self-preservation mechanism may be formed due to OBC. The horizontal area influenced by oasis is twice as oasis area and the vertical range is four times as oasis. The ODC is strong in the daytime and reaches the strongest at 17:00, and the influenced area is the largest at 20:00. 相似文献
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We study the importance of the zones of weakness and the pattern of downgoing flow in steady-state models of subducting lithosphere, which interacts mechanically and thermally with the ambient mantle. The non-linear system of governing equations consists of (i) the momentum equation in stream function formulation and (ii) the steady-state heat transfer equation including conduction and advection of heat and dissipation. A finite element method has been applied to this system. We consider the viscosity to be a non-linear function of both the temperature and the stream function. In steady-state two-dimensional (2D) flow, the stream function isolines follow material trajectories. They are used to follow the top of the subducting slab, which because of its possible increase in water content, is assumed to have a lower viscosity. The zone of weakness has been thus obtained in the self-consistent fashion since the stream function as well as the temperature are the output from our modeling and no a priori assumptions about the shape of the bending lithosphere are taken into account. It was shown that several orders decrease of viscosity in the zone of weakness is required to obtain the dip angle of about 45°. If the decrease of viscosity is not sufficient enough, the subducted slab either sinks almost vertically or does not exhibit a plate-like behavior. We have also demonstrated that shear heating can unrealistically increase at the zone of weakness for fast subductions if decrease of viscosity is underestimated. 相似文献
88.
A Modeling Study of the Effects of Anomalous Snow Cover over the Tibetan Plateau upon the South Asian Summer Monsoon 总被引:1,自引:0,他引:1
The effect of anomalous snow cover over the Tibetan Plateau upon the South Asian summer monsoon is investigated by numerical simulations using the NCAR regional climate model (RegCM2) into which gravity wave drag has been introduced. The simulations adopt relatively realistic snow mass forcings based on Scanning Multi-channel Microwave Radiometer (SNINIR) pentad snow depth data. The physical mechanism and spatial structure of the sensitivity of the South Asian early summer monsoon to snow cover anomaly over the Tibetan Plateau are revealed. The main results are summarized as follows. The heavier than normal snow cover over the Plateau can obviously reduce the shortwave radiation absorbed by surface through the albedo effect, which is compensated by weaker upward sensible heat flux associated with colder surface temperature, whereas the effects of snow melting and evaporation are relatively smaller.The anomalies of surface heat fluxes can last until June and become unobvious in July. The decrease of the Plateau surface temperature caused by heavier snow cover reaches its maximum value from late April to early May. The atmospheric cooling in the mid-upper troposphere over the Plateau and its surrounding areas is most obvious in May and can keep a fairly strong intensity in June. In contrast, there is warming to the south of the Plateau in the mid-lower troposphere from April to June with a maximum value in May.The heavier snow cover over the Plateau can reduce the intensity of the South Asian summer monsoon and rainfall to some extent, but this influence is only obvious in early summer and almost disappears in later stages. 相似文献
89.
新疆阿尔泰造山带构造作用的锆石裂变径迹分析 总被引:1,自引:0,他引:1
在新疆阿尔泰造山带所获得的19个锆石裂变径迹年龄变化于155-243Ma之间,明显地分为2组,分别对应于2个构造活动期,早期为155-189Ma,晚期为189-243Ma。这与磷灰石裂变径迹年龄反映的62-100Ma和100-160Ma两个构造期完全一致。早期和晚期构造活动期持续的时间分别为54-60Ma和34-38Ma,而这两个构造期之间的间隔时间,则从早到晚由83-89Ma变为89-93Ma。同时,锆石裂变径迹年龄与距特斯巴汗断裂和巴寨断裂的距离有关,反映这两条断裂带对区域构造演化的控制作用。 相似文献
90.
The phase relations of quaternary systems are generally represented by projections onto ternary compositional planes. Such
projections often obscure relationships that would only be evident in a three-dimensional tetrahedral plot. The tetrahedral
plot requires that compositions of the minerals and melts be transformed into Cartesian coordinates. It is shown here how
this transformation is carried out. The application is demonstrated by tetrahedral plots of experimental melt compositions
of partially molten lherzolite. Furthermore, the plot can be used to evaluate whether or not a particular basaltic composition
represents a primary melt. The methods are applicable to any four-component system. 相似文献