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181.
Uncertainty forecasting in orbital mechanics is an essential but difficult task, primarily because the underlying Fokker–Planck equation (FPE) is defined on a relatively high dimensional (6-D) state–space and is driven by the nonlinear perturbed Keplerian dynamics. In addition, an enormously large solution domain is required for numerical solution of this FPE (e.g. encompassing the entire orbit in the \(x-y-z\) subspace), of which the state probability density function (pdf) occupies a tiny fraction at any given time. This coupling of large size, high dimensionality and nonlinearity makes for a formidable computational task, and has caused the FPE for orbital uncertainty propagation to remain an unsolved problem. To the best of the authors’ knowledge, this paper presents the first successful direct solution of the FPE for perturbed Keplerian mechanics. To tackle the dimensionality issue, the time-varying state pdf is approximated in the CANDECOMP/PARAFAC decomposition tensor form where all the six spatial dimensions as well as the time dimension are separated from one other. The pdf approximation for all times is obtained simultaneously via the alternating least squares algorithm. Chebyshev spectral differentiation is employed for discretization on account of its spectral (“super-fast”) convergence rate. To facilitate the tensor decomposition and control the solution domain size, system dynamics is expressed using spherical coordinates in a noninertial reference frame. Numerical results obtained on a regular personal computer are compared with Monte Carlo simulations. 相似文献
182.
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
183.
Introduction The Western Kunlun Mountain Pass M=8.1 earthquake occurred on November 14, 2001 is the other M=8 earthquake occurred 50 years after Dangxiong, Tibet M=8.0 earthquake in Chinese mainland. The earthquake has caused the attention of the seismologists in the following aspects: 1) The fracture length is more than 400 km, which is far away from the estimated length by the statistic empirical function between the magnitude and the fracture length (WANG, et al, 2002); 2) The aftersh… 相似文献
184.
185.
Magma plumbing beneath Anak Krakatau volcano, Indonesia: evidence for multiple magma storage regions
B?rje Dahren Valentin R. Troll Ulf B. Andersson Jane P. Chadwick Màiri F. Gardner Kairly Jaxybulatov Ivan Koulakov 《Contributions to Mineralogy and Petrology》2012,163(4):631-651
Understanding magma plumbing is essential for predicting the behaviour of explosive volcanoes. We investigate magma plumbing
at the highly active Anak Krakatau volcano (Indonesia), situated on the rim of the 1883 Krakatau caldera by employing a suite
of thermobarometric models. These include clinopyroxene-melt thermobarometry, plagioclase-melt thermobarometry, clinopyroxene
composition barometry and olivine-melt thermometry. Petrological studies have previously identified shallow magma storage
in the region of 2–8 km beneath Krakatau, while existing seismic evidence points towards mid- to deep-crustal storage zone(s),
at 9 and 22 km, respectively. Our results show that clinopyroxene in Anak Krakatau lavas crystallized at a depth of 7–12 km,
while plagioclase records both shallow crustal (3–7 km) and sub-Moho (23–28 km) levels of crystallization. These magma storage
regions coincide with well-constrained major lithological boundaries in the crust, implying that magma ascent and storage
at Anak Krakatau is strongly controlled by crustal properties. A tandem seismic tomography survey independently identified
a separate upper crustal (<7 km) and a lower to mid-crustal magma storage region (>7 km). Both petrological and seismic methods
are sensitive in detecting magma bodies in the crust, but suffer from various limitations. Combined geophysical and petrological
surveys, in turn, offer increased potential for a comprehensive characterization of magma plumbing at active volcanic complexes. 相似文献
186.
Jacek?StankiewiczEmail author Michael?H.?Weber Ayman?Mohsen Rami?Hofstetter 《Pure and Applied Geophysics》2012,169(4):615-623
In the framework of the Dead Sea Integrated Research project (DESIRE), 59 seismological stations were deployed in the region
of the Dead Sea Basin. Twenty of these stations recorded data of sufficiently high quality between May and September 2007
to be used for ambient seismic noise analysis. Empirical Green’s functions are extracted from cross-correlations of long term
recordings. These functions are dominated by Rayleigh waves, whose group velocities can be measured in the frequency range
from 0.1 to 0.5 Hz. Analysis of positive and negative correlation lags of the Green’s functions makes it possible to identify
the direction of the source of the incoming energy. Signals with frequencies higher than 0.2 Hz originate from the Mediterranean
Sea, while low frequencies arrive from the direction of the Red Sea. Travel times of the extracted Rayleigh waves were measured
between station pairs for different frequencies, and tomographically inverted to provide independent velocity models. Four
such 2D models were computed for a set of frequencies, all corresponding to different sampling depths, and thus together giving
an indication of the velocity variations in 3D extending to a depth of 10 km. The results show low velocities in the Dead
Sea Basin, consistent with previous studies suggesting up to 8 km of recent sedimentary infill in the Basin. The complex structure
of the western margin of the Basin is also observed, with sedimentary infill present to depths not exceeding 5 km west of
the southern part of the Dead Sea. The high velocities associated with the Lisan salt diapir are also observed down to a depth
of ~5 km. The reliability of the results is confirmed by checkerboard recovery tests. 相似文献
187.
根据近场强震台加速度记录对2011年10月12日北京市石景山区ML2.1地震的加速度影响场进行了计算分析.同时使用了首都圈宽频带数字台站记录数据通过P波初动格点尝试法解算出该地震的震源机制解,并与加速度影响场进行对比研究.结果表明,此次地震加速度影响场水平向加速度高于垂直向;水平向峰值加速度分布区和加速度影响场高低速度过渡区总体呈EW向或NEE向分布,与震源机制解结果的两个节面走向较为一致;加速度衰减NS向快于EW向.本文研究结果可为强震或较大地震发生后快速判定震害影响场提供参考依据. 相似文献
188.
成都市民消费结构与休闲活动关系研究 总被引:6,自引:0,他引:6
城市居民消费水平,消费结构会影响其休闲消费能力,消费意愿,消费方式,消费态度和休闲时空结构,文章以成都市7个城区歌舞,茶棋牌,电影及城市公园休闲活动调查为基础,探讨了城市居民消费结构及其变化与休闲活动特征的关系。研究结果表明,城市居民消费结构的改变对歌舞,茶棋牌娱乐活动影响最大。 相似文献
189.
190.
Edward?VenzkeEmail author Sally?Kuhn?Sennert Richard?Wunderman 《Bulletin of Volcanology》2009,71(4):475-476
Information included in this summary is based on more detailed reports published in the Bulletin of the Global Volcanism Network,
vol. 33, no. 9, September 2008 (on the Internet at ). Edited by scientists at the Smithsonian, this bulletin includes reports provided by a worldwide network of correspondents.
The reports contain the names and contact information for all sources. Please note that these reports are preliminary and
subject to change as events are studied in more detail. The Global Volcanism Program welcomes further reports of current volcanism,
seismic unrest, monitoring data, and field observations. 相似文献