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   

Geopotential Reconstruction,Decomposition, Fast Computation,and Noise Cancellation by Harmonic Wavelets     

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   

On the Models of the Lower Mantle Viscosity Consistent with the Modern Data of Core-Mantle Boundary Flattening     

Molodensky  S. M.  Groten  E. 《Studia Geophysica et Geodaetica》2002,46(3):411-433

In Forte and Claire Perry (2000) models of mantle viscosity (by using the data on tectonic plate velocities, of global free-air gravity anomalies, of surface topography corrected for crustal isostasy, and the excess of dynamic ellipticity of the core-mantle boundary in accordance with Herring et al., 1986 and Mathews et al., 1999) have been constructed. In the following investigation we reconsider the results which are obtained from the presently available data on core-mantle boundary flattening (abbreviated by CMBF). In contrast with the aforementioned work, we use below the value of CMBF (Molodensky and Groten, 1998) which is based on a new approach to the theory of diurnal Earth tides and nutation which takes into account the second-order terms of expansions of a small parameter (for a detailed discussion of this subject see (Molodensky and Groten, 1998)). Below we find the area of admissible values of mantle viscosity which does not contradict the following data sets: (a) the numerical value on CMBF; (b) the value of the whole Earth's dynamical flattening, and (c) the data on the secular deceleration of the Earth's rotation. Our estimations show, that the maximal viscosity at depth 2000 km may be of the order of 10²⁷ Poise. This value is consistent with the distribution obtained by Trubitsin (2000) who adopted the viscosity dependence on temperature and pressure by an exponential function with olivine parameters under the assumption that the activation energy varies only weakly with pressure, and the activation volume varies in inverse proportion to temperature. Under these assumptions, his solution of convection equations gave the depth dependence of temperature and thereby the viscosity distribution.  相似文献   

Modeling Dust Jets And Shells From Comet Hale-Bopp     

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   

Der Einfluss der freien Ozeane auf die Bestimmung des Verhaltens der Erdkruste aus Horizontalpendelmessungen     

Dipl. Ing. Erwin Groten 《Pure and Applied Geophysics》1963,54(1):6-24

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On the relation between the peak frequency and the corresponding rise time of solar microwave impulsive bursts and the height dependence of magnetic fields     

Zhao Ren-Yang  Andreas Magun  Erwin Schanda 《Solar physics》1990,130(1-2):361-368

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   

The Problem of Gravitational Absorption     

Erwin Groten 《Geophysical Journal International》1972,27(4):447-448

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Conventional and in situ geochronology of the Teplá Crystalline unit, Bohemian Massif: implications for the processes involving monazite formation     

Hilke Timmermann  Wolfgang Dörr  Erwin Krenn  Fritz Finger  Gernold Zulauf 《International Journal of Earth Sciences》2006,95(4):629-647

The Teplá Crystalline unit (TCU), western Bohemian Massif, proves highly suitable for studying the effects of differential metamorphic reworking on the U–Th–Pb systematics in monazite, as the overprint of Variscan regional metamorphism onto high-grade Cadomian paragneisses intensifies progressively towards the northwest. Although variably hampered by scarcity, small size, and low uranium contents of monazite, isotope dilution–thermal ionisation mass spectrometry of monazite from paragneisses from the garnet, staurolite, and kyanite zones of the TCU gives a narrow ²⁰⁶Pb/²³⁸U age range from 387 to 382 Ma for Variscan peak metamorphism. These data are supported by 382–373 Ma monazite ages derived from electron microprobe analyses. Inheritance of older components in grains from the central TCU imply major “resetting” of pre-Variscan monazite around 380 Ma, possibly due to widespread garnet growth during Variscan metamorphism, which led to the consumption of pre-Variscan high-Y monazite and subsequent growth of new low-Y monazite. Concordant 498–494 Ma monazite ages in a migmatitic paragneiss close to the adjacent Mariánské Lázně Complex (MLC) grew in response to metagabbro emplacement in the MLC from 503 to 496 Ma and not during either Cadomian or Variscan regional metamorphism. Backscatter imaging and electron microprobe analyses reveal that discordant monazite of the migmatite comprises a mix of various age domains that range from ca. 540 to 380 Ma. Combined evidence presented here suggests that instead of Pb loss by volume diffusion, the apparent resetting of the U–Th–Pb systematics in monazite rather involves new crystal growth or regrowth by recrystallisation and dissolution/reprecipitation.  相似文献   

Surface elevation dynamics in vegetatedSpartina marshes versus unvegetated tidal ponds along the Mid-Atlantic coast, USA, with implications to waterbirds   总被引：1，自引：0，他引：1  

R. Michael Erwin  Donald R. Cahoon  Diann J. Prosser  Geoffrey M. Sanders  Phillippe Hensel 《Estuaries and Coasts》2006,29(1):96-106

Mid Atlantic coastal salt marshes contain a matrix of vegetation diversified by tidal pools, pannes, and creeks, providing habitats of varying importance to many species of breeding, migrating, and wintering waterbirds. We hypothesized that changes in marsh elevation were not sufficient to keep pace with those of sea level in both vegetated and unvegetatedSpartina alterniflora sites at a number of mid lagoon marsh areas along the Atlantic Coast. We also predicted that northern areas would suffer less of a deficit than would southern sites. Beginning in August 1998, we installed surface elevation tables at study sites on Cape Cod, Massachusetts, southern New Jersey, and two locations along Virginia's eastern shore. We compared these elevation changes over the 4–4.5 yr record with the long-term (>50 yr) tidal records for each locale. We also collected data on waterbird use of these sites during all seasons of the year, based on ground surveys and replicated surveys from observation platforms. Three patterns of marsh elevation change were found. At Nauset Marsh, Cape Cod, theSpartina marsh surface tracked the pond surface, both keeping pace with regional sea-level rise rates. In New Jersey, the ponds are becoming deeper while marsh surface elevation remains unchanged from the initial reading. This may result in a submergence of the marsh in the future, assuming sea-level rise continues at current rates. Ponds at both Virginia sites are filling in, while marsh surface elevation rates do not seem to be keeping pace with local sea-level rise. An additional finding at all sites was that subsidence in the vegetated marsh surfaces was less than in unvegetated areas, reflecting the importance of the root mat in stabilizing sediments. The implications to migratory waterbirds are significant. Submergence of much of the lagoonal marsh area in Virginia and New Jersey over the next century could have major negative (i.e., flooding) effects on nesting populations of marsh-dependent seaside sparrowsAmmodramus maritimus, saltmarsh sharp-tailed sparrowsAmmodramus caudacutus, black railsLaterallus jamaicensis, clapper railsRallus longirostris. Forster's ternsSterna forsteri, common ternsSterna hirundo, and gull-billed ternsSterna nilotica. Although short-term inundation of many lagoonal marshes may benefit some open-water feeding ducks, geese, and swans during winter, the long-term ecosystem effects may be detrimental, as wildlife resources will be lost or displaced. With the reduction in area of emergent marsh, estuarine secondary productivity and biotic diversity will also be reduced.  相似文献   

Intersections of remanence small circles: new tools to improve data processing and interpretation in palaeomagnetism   总被引：1，自引：0，他引：1  

Martin Waldhör  Erwin Appel 《Geophysical Journal International》2006,166(1):33-45

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