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331.
G. A. Moiseev 《Physical Oceanography》1993,4(3):183-192
The idea of the weak variability of the fields is introduced, which means that when they are recorded by some measuring instrument (MI), the output signal obtains increments of the order of one/several quanta of sensitivity at the discreteness interval. At small scales (microstructure), this field is described in terms of random discrete values which reflect the properties of both the field measured and the MI. Theoretical relationships which define the probabilities of increments at the compound intervals in terms of the probabilities of increments at the sampling intervals, are derived for the case of independent random increments at the sampling intervals of discreteness. The validity of this model is illustrated by respective computations using data of microstructure measurements of the temperature profile in the main thermocline in the Sargasso Sea.Translated by Mikhail M. Trufanov. 相似文献
332.
An ensemble of twenty-three 14-year experiments conducted with the ECHAM-4 GCM has been examined to test the model's capability
to simulate the principal modes of interannual variability. The integrations were performed under specified monthly SST between
1979–1993. The analysis was focused on the Southern Hemisphere (SH) extratropics. Empirical orthogonal functions analysis
(EOF) using seasonal anomaly fields has been performed to isolate the principal modes that dominate the southern extratropical
variability at the interannual time scale. Leading patterns of 500 hPa geopotential height (z500) have been compared with
those estimated from the ECMWF re-analysis dataset. The model is able to adequately reproduce the spatial pattern of the annular
mode, but it represents the temporal variations of the oscillation less satisfactorily. The model simulation of the Pacific
South American (PSA) pattern is better, both in the shape of the pattern and in the temporal evolution. To verify if the capability
of the model to adequately simulate the temporal oscillation of the propagating patterns is related to the increased influence
of the tropical external forcing, covarying SST-atmospheric modes have been identified by singular value decomposition (SVD).
In winter (July-August-September, JAS) the tropical SST variability is highly correlated with the ENSO mode. In summer (January-February-March,
JFM) the strength of the teleconnections is related to strong westerly anomalies, disrupted by a meridional out of phase relation
near to South America. The large size of the ensemble was exploited by comparing the time-varying model spread and degrees
of freedom of the simulated extratropical circulation. Results show that when the extratropical circulation has a few degrees
of freedom, the reproducibility is relatively low and the ensemble is governed by a fairly robust zonally symmetric structure
of dispersion.
Received: 9 May 2000 / Accepted: 30 January 2001 相似文献
333.
Results are presented for polarimetric observations of 17 red giants and supergiants, of which nine are long-period Mira variables, five are semiregular variables (SR), and three are slowly fluctuating variables (Lb). Light polarization is detected for eight stars, seven of them for the first time.Translated fromAstrofizika, Vol. 39, No. 3, pp. 385–391, July–September, 1996. 相似文献
334.
G. A. Krasinsky 《Celestial Mechanics and Dynamical Astronomy》2002,84(1):27-55
Differential equations describing the tidal evolution of the earth's rotation and of the lunar orbital motion are presented in a simple close form. The equations differ in form for orbits fixed to the terrestrial equator and for orbits with the nodes precessing along the ecliptic due to solar perturbations. Analytical considerations show that if the contemporary lunar orbit were equatorial the evolution would develop from an unstable geosynchronous orbit of the period about 4.42 h (in the past) to a stable geosynchronous orbit of the period about 44.8 days (in the future). It is also demonstrated that at the contemporary epoch the orbital plane of the fictitious equatorial moon would be unstable in the Liapunov's sense, being asymptotically stable at early stages of the evolution. Evolution of the currently near-ecliptical lunar orbit and of the terrestrial rotation is traced backward in time by numerical integration of the evolutional equations. It is confirmed that about 1.8 billion years ago a critical phase of the evolution took place when the equatorial inclination of the moon reached small values and the moon was in a near vicinity of the earth. Before the critical epoch t
cr
two types of the evolution are possible, which at present cannot be unambiguously distinguished with the help of the purely dynamical considerations. In the scenario that seems to be the most realistic from the physical point of view, the evolution also has started from a geosynchronous equatorial lunar orbit of the period 4.19 h. At t < t
cr
the lunar orbit has been fixed to the precessing terrestrial equator by strong perturbations from the earth's flattening and by tidal effects; at the critical epoch the solar perturbations begin to dominate and transfer the moon to its contemporary near-ecliptical orbit which evolves now to the stable geosynchronous state. Probably this scenario is in favour of the Darwin's hypothesis about originating the moon by its separation from the earth. Too much short time scale of the evolution in this model might be enlarged if the dissipative Q factor had somewhat larger values in the past than in the present epoch. Values of the length of day and the length of month, estimated from paleontological data, are confronted with the results of the developed model. 相似文献
335.
We briefly describe an advanced 3D gas dynamical model developed for the simulation of theenvironment of active cometary nuclei.
The model canhandle realistic nucleus shapes and alternative physical models for the gas and dust production mechanism.The
inner gas coma structure is computed by solving self-consistently(a) near to the surface the Boltzman Equation(b) outside
of it, Euler or Navier-Stokes equations.The dust distribution is computed from multifluid ``zero-temperature' Euler equations,extrapolated
with the help of a Keplerian fountain model.The evolution of the coma during the nucleus orbital and spin motion,is computed
as a succession of quasi-steady solutions. Earlier versions of the model using simple,``paedagogic' nuclei have demonstrated
that the surface orographyand the surface inhomogeneity contribute similarly to structuring the near-nucleusgas and dust coma,casting
a shadow on the automatic attribution of such structures to ``active areas'.The model was recently applied to comet P/Halley,
for whichthe nucleus shape is available. In the companion paper of this volume,we show that most near-nucleus dust structuresobserved
during the 1986 Halley flybys are reproduced, assuming that the nucleus is strictly homogeneous. Here, we investigate the
effect of shape perturbations and homogeneityperturbations. We show that the near nucleus gas coma structure is robust vis-a-vissuch
effects. In particular, a random distribution of active and inactive areaswould not affect considerably this structure, suggesting that such areas,even if present, could not be easily identified on images
of the coma. 相似文献
336.
The propagation of axisymmetric magnetohydrodynamic waves near the equatorial plane of the crust of a neutron star in a transverse magnetic field is considered. The magnetic field is perpendicular to the equatorial plane. The magnetic fields and electric currents excited by this wave beam at the stellar surface are determined. 相似文献
337.
338.
The purpose of this work was to reinvestigate the existing hydrogeological conceptual model of the basin of Madrid, Spain. A cumulative chemical isotopic diagram which enabled the distinction between different groups of water as well as calculation of the mode of their blending was used for this investigation. It was found that the groups of discharge were lighter in their isotopic composition than that of recharge. The previous explanation of this fact, backed by carbon-14 dating, was the long residence time due to flow lines going down to depths of more than 1000 m. This flow model assumes homogenous conditions to these depths. This assumption can not be supported by evidence from deep wells. Thus a modified model is suggested which maintains homogenous conditions only to about 300 m and a deep confined aquifer below containing paleowater. The higher degree of depletion of this water has been explained by a colder climate on top of an altitude effect. Another interesting observation was the correlation between the isotopic composition of the rains, the month of the rain event and the composition of the recharge group groundwater. It could be seen that the winter rains resemble the groundwater composition, which shows that practically all the spring and summer rains were evapotranspirated. 相似文献
339.
Yu. G. Shkuratov K. Muinonen E. Bowell K. Lumme J. I. Peltoniemi M. A. Kreslavsky D. G. Stankevich V. P. Tishkovetz N. V. Opanasenko L. Y. Melkumova 《Earth, Moon, and Planets》1994,65(3):201-246
About a dozen physical mechanisms and models aspire to explain the negative polarization of light scattered by atmosphereless celestial bodies. This is too large a number for the reliable interpretation of observational data. Through a comparative analysis of the models, our main goal is to answer the question: Does any one model have an advantage over the others? Our analysis is based on new laboratory polarimetric and photometric data as well as on theoretical results. We show that the widely used models due to Hopfield and Wolff cannot realistically explain the phase-angle dependence of the degree of polarization observed at small phase angles. The so-called interference or coherent backscattering mechanism is the most promising model. Models based on that mechanism use well-defined physical parameters to explain both negative polarization and the opposition effect. They are supported by laboratory experiments, particularly those showing enhancement of negative polarization with decreasing particle size down to the wavelength of light. According to the interference mechanism, pronounced negative branches of polarization, like those of C-class asteroids, may indicate a high degree of optical inhomogeneity of light-scattering surfaces at small scales. The mechanism also seems appropriate for treating the negative polarization and opposition effects of cometary dust comae, planetary rings, and the zodiacal light. 相似文献
340.
F. W. Shotton D. H. Keen G. R. Coope A. P. Currant P. L. Gibbard M. Aalto S. M. Peglar J. E. Robinson 《第四纪科学杂志》1993,8(4):293-325
A complex of channels underlying the Baginton-Lillington Gravel (Baginton Formation) at Waverley Wood Quarry, Warwickshire is described. Fossil pollen and plant macrofossils, Coleoptera, Ostracoda, Mollusca and Mammalia are described from the channel-fill deposits. Consideration of all the evidence allows the identification of four separate stages of channel fill which largely occurred under a cool temperate climate. At the top of Channel 2 evidence for a cold, continental climatic episode can be recognised, suggesting that the whole complex was deposited under a fluctuating climate at the end of a temperate stage. At two levels in the channels human artefacts were recovered confirming the presence of Palaeolithic people in Warwickshire during the deposition of the sediments. Amino-acid geochronology suggests an age within the ‘Cromerian Complex’ Stage for the channels. The small vertebrate and molluscan faunas indicate that the deposits are no older than the latter part of the ‘Cromerian Complex’ Stage of East Anglia. The regional stratigraphic significance of the Waverley Wood succession is outlined. 相似文献