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排序方式: 共有159条查询结果,搜索用时 234 毫秒
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We have computed estimates of the rate of vertical land motion in the Mediterranean Sea from differences of sea level heights measured by the TOPEX/Poseidon radar altimeter and by a set of tide gauge stations. The comparison of data at 16 tide gauges, using both hourly data from local datasets and monthly data from the PSMSL dataset, shows a general agreement, significant differences are found at only one location. Differences of near-simultaneous, monthly and deseasoned monthly sea level height time-series have been considered in order to reduce the error in the estimated linear-term. In a subset of 23 tide gauge stations the mean accuracy of the estimated vertical rates is 2.3 ± 0.8 mm/yr. Results for various stations are in agreement with estimates of vertical land motion from geodetic methods. A comparison with vertical motion estimated by GPS at four locations shows a mean difference of -0.04 ± 1.8 mm/yr, however the length of the GPS time-series and the number of locations are too small to draw general conclusions. 相似文献
145.
Comparison of Earth’s magnetospheric magnetic field models in the context of cosmic ray physics 总被引:1,自引:0,他引:1
Laurent Desorgher Karel Kudela Erwin O. Flückiger Rolf Bütikofer Marisa Storini Vladimir Kalegaev 《Acta Geophysica》2009,57(1):75-87
Over the last two decades, models of the Earth’s magnetospheric magnetic field have been continuously improved to describe
more precisely the different magnetospheric current systems (magnetopause current, symmetric and partial ring currents, tail
currents and field aligned currents). In this paper we compare the different Tsyganenko models and the Alexeev and Feldstein
model in the context of cosmic ray physics. We compare the vertical cutoff rigidity and asymptotic direction of vertical incidence
obtained with these models for the January 20, 2005, ground level enhancement and for the big magnetic storm of April 6, 2000.
For the event of January 20, 2005, we study the impact of the differences in asymptotic direction obtained with the models
on the radiation dose computation at aircraft altitude. For the magnetic storm of April 6, 2000, we discuss the importance
of the different magnetospheric current systems in causing cutoff rigidity variations. Finally we summarise the advantages
and drawbacks of the different models in the context of space weather. 相似文献
146.
Freeden Willi Groten Erwin Michel Volker Arfa-Kaboodvand Kourosh 《Studia Geophysica et Geodaetica》2003,47(1):37-72
Harmonic wavelets are introduced within the framework of the Sobolev-like Hilbert space H of potentials with square-integrable restrictions to the Earth's (mean) sphere
R
. Basic tool is the construction of H-product kernels in terms of an (outer harmonics) orthonormal basis in H. Scaling function and wavelet are defined by means of so-called H-product kernels. Harmonic wavelets are shown to be building blocks that decorrelate geopotential data. A pyramid scheme enables fast computations. Multiscale signal-to-noise thresholding provides suitable denoising. Multiscale modelling of the Earth's anomalous potential from EGM96-model data is illustrated by use of bandlimited harmonic wavelets, i.e. Shannon and CP-wavelets. 相似文献
147.
Vasundhara R. Chakraborty Pavan Hänel Andreas Heiser Erwin 《Earth, Moon, and Planets》1997,78(1-3):321-328
Persistent jet and shell structures from comet Hale-Bopp showing gradual changes in the shapes and orientations with aspect
angle and solar illumination geometry indicate long lived active sources. A model to simulate the dust features has been applied
to the series of observations from September 1996 to May 1997. Most of the structures can be explained as arising due to ejections
from persistent active regions at comet-o-centric latitudes near +65°, +55°, −5° to −15°, −35° and −65°. The best fitting
pole positions vary between 255° ±10° and 275° ± 10° in right ascension and −45° ± 10° to −75° ± 10° in declination. Lower
limits on the dust and gas production rates at various epochs are presented.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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149.
In the present paper we report the results of a correlation analysis for 57 microwave impulsive bursts observed at six frequencies in which we have obtained a regression line between the peak frequency and the corresponding rise time of microwave impulsive bursts: {ie361-01} (with a correlation coefficient of - 0.43). This can be explained in the frame of a thermal model. The magnetic field decrease with height has to be much slower than in a dipole field in order to explain the weak dependence of f
p
on t
r
. This decrease of magnetic field with height in burst sources is based on the relationship between f
p
and t
r
found by assuming a thermal flare model with a collisionless conduction front.On leave from Beijing Observatory, Academia Sinica, Beijing, China. 相似文献
150.