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661.
662.
A. G. Lyne R. S. Pritchard F. Graham-Smith 《Monthly notices of the Royal Astronomical Society》2001,321(1):67-70
Between 1997 August and October, the radio pulses from the Crab pulsar were followed by discrete moving echoes, which appear to be reflections from part of an ionized shell in the outer part of the Crab Nebula, crossing the line of sight to pulsar. Similar events have now been recognized in recordings from the past 30 yr, and it seems that the Nebula must contain a large number of ionized shell-like surfaces on a much finer scale than recognized hitherto. 相似文献
663.
Geomagnetic storms driven by solar eruptions are known to have significant effects on the total density of the upper atmosphere
in the altitude range 250–1000 km. This in turn causes a measurable effect on the orbits of resident space objects in this
altitude range. We analyzed a sample of these orbits, both from sensor data and from orbital element sets, during the period
surrounding the 14 July 2000 solar activity. We present information concerning the effects of this event on the orbits of
resident space objects and how well accepted atmospheric models were able to represent it. As part of this analysis, we describe
a technique for extracting atmospheric density information from orbital element sets. On daily time scales, the effect of
geomagnetic activity appears to be more important than that of prompt radiation. However, the limitations in time and amplitude
quantization of the accepted solar indices are evident. A limited comparison is also made with previous solar storm events. 相似文献
664.
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
665.
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
666.
We examine the long-term seismicity of the Marmara Sea region in Turkey over a period of twenty centuries to attempt to answer two questions: (1) how well recorded in history is the earthquake activity of this region? and (2) does seismicity over this long period of time differ from that over the present century? We study this densely-populated and fast-developing region because it is one of the most tectonically active regions on the continents that appears today to be relatively quiescent. 相似文献
667.
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
668.
We have digitized the Ca ii K spectroheliograms, observed at the National Solar Observatory at Sacramento Peak, for the period 1980 (maximum of solar cycle 21), 1985 (minimum of solar cycle 21), 1987 (beginning of the ascending phase of solar cycle 22), 1988 and 1989 (ascending phase and maximum of solar cycle 22), and 1992 (declining phase of solar cycle 22). A new method for analyzing the K spectroheliograms has been developed and applied to the K images for the time interval of 1992. Using histograms of intensity, we have segregated and measured the cumulative intensity and area of various chromospheric features like the plages, magnetic network and intranetwork elements. Also, the full width at half maximum (FWHM) derived from the histograms has been introduced as a new index for describing the chromospheric activity in the K-line. The full-disk intensity (spatial K index) has been derived from spatially-resolved K images and compared to the spectral K index derived from the line profiles for the full disk. Both the spatial K index and FWHM have been compared to the UV irradiance measured in the Mg ii h and k lines by the NOAA9 satellite and found that they are highly correlated with the Mg ii h and k c/w ratio.NRC Resident Research Associate, on leave from Indian Institute of Astrophysics, Bangalore 560034, India. 相似文献
669.
R. K. Thakur 《Astrophysics and Space Science》1993,199(1):159-164
It is suggested that a collapsing supermassive object, which acts as an ultra-high energy particle accelerator, is the precursor of an active galactic nucleus and that the gravitational energy released during the collapse of the object is locked in the quark-gluon plasma permeated by leptons into which the entire matter in the core of the object is converted as a result of the collapse. It is also pointed out that the collapse of the object to a space-time singularity is inhibited by Pauli's exclusion principle as well as by Heisenberg's uncertainty principle and that the object explodes, before it could collapse to a singularity, thereby releasing the enormous amount of energy locked in the quark-gluon plasma. 相似文献
670.