An empirical model of the daily evolution of the coronal index     

Mavromichalaki  H.  Plainaki  C.  Zouganelis  I.  Petropoulos  B. 《Solar physics》2003,218(1-2):63-78

Global changes of the solar activity can be expressed by the coronal index that is based upon the total irradiance of the coronal 530.3 nm green line from observations at five stations. Daily mean values of the coronal index of solar activity and other well-correlated solar indices are analyzed for the period 1966–1998 covering over three solar cycles. The significant correlation of this index with the sunspot number and the solar flare index have led to an analytical expression which can reproduce the coronal index of solar activity as a function of these parameters. This expression explains well the existence of the two maxima during the solar cycles taking into account the evolution of the magnetic field that can be expressed by some sinusoidal terms during solar maxima and minima. The accuracy between observed and calculated values of the coronal index on a daily basis reaches the value of 71%. It is concluded that the representative character of the coronal index is preserved even when using daily data and can therefore allow us to study long-term, intermediate and short-term variations for the Sun as a star, in association with different periodical solar–terrestrial phenomena useful for space weather studies.  相似文献   

Solar-planetary cycles in Jupiter's great red spot darkness     

I. Liritzis  B. Petropoulos  C. Banos  E. Sarris 《Earth, Moon, and Planets》1996,73(2):167-179

The change in the darkness of the Great Red Spot (GRS) of Jupiter (1894–1974) has been analysed with Fourier (FFT), Maximum Entropy and Power spectrum (Blackman-Tukey window) (PSA) methods of spectrum analysis. Significance, non-randomness and stationarity tests assigned high variance to periodicities of 33 ± 4, 13–15, about 11, 9 and 3 yrs. The highest correlation between solar activity and GRS darkness was found for the 14th and 16th solar cycle. The periodicities obtained are interpreted as the combined eftects of solar activity, planetary resonances and internal jovian mechanisms.  相似文献   

Analysis of mapping coverage obtained from spacecraft     

Anastassios E. Petropoulos  James M. Longuski 《Celestial Mechanics and Dynamical Astronomy》1994,60(4):431-454

An exact analysis of the coverage obtained by spacecraft using cross-track scanning and nadir-centered conical imaging, under imposed viewing obliqueness and resolution requirements, is presented. In addition to exact expressions for the area acquired and the area acquisition rate, envelope theory is introduced to obtain the boundary of the imaged area. These expressions are relatively compact, allowing rapid machine computation. The effects of the sun phase angle, and of imaging system limitations are also examined. The Galileo mission encounter with Callisto is used as a numerical example, from which certain general conclusions are drawn regarding optimal imaging trajectories.  相似文献   

Physical parameters of the atmosphere of Venus from Venera 15 and 16 missions     

B. Petropoulos  P. Telonis 《Earth, Moon, and Planets》1993,63(1):1-7

The following physical parameters have been computed for the atmosphere of Venus between 65 and 90 km, by intervals of 1 km. (1) Pressure, (2) Density, (3) Speed of sound, (4) Number density, (5) Density scale, (6) Pressure scale, (7) Collisional frequency, (8) Mean particle velocity (9) Mean free path, (10) Columnar mass, (11) Viscosity. For these calculations we have used the temperature altitude measurements of Venera 15 and 16 at 52 °N and 72 °N latitudes, the night and 70 °N and 72 °N latitudes the day.  相似文献   

Physical parameters of the Jovian atmosphere     

C. J. Banos  B. Petropoulos 《Earth, Moon, and Planets》1988,42(1):19-28

The following physical parameters have been computed for the Jovian atmosphere between 270 and ?300 km: (1) Pressure, (2) Density, (3) Speed and sound, (4) Number density, (5) Density scale. It has considered that the top of the clouds is at 0 km. For the calculations of these parameters we have used:

1. for the altitudes 270-0 km data from Voyager I and II.
2. for the altitudes ?300–0 km data from Voyager II and spectroscopic observations.

  相似文献   

The evolution and the secondary maximum of the green line intensity     

J. Xanthakis  B. Petropoulos  H. Mavromichalaki 《Solar physics》1982,76(1):181-190

A new relation has been given in order to calculate the intensity of the green line of the solar corona at 5303 Å as a function of the number of proton events N _P and the R (R) index of solar activity. This relation is available for the 19th and 20th solar cycles. Moreover there is given a theoretical justification of this relationship taking into account as a new parameter the evolution of the coronal magnetic field during the solar cycle.  相似文献   

Relationship between crustal finite strain and seismic anisotropy in the mantle, Pacific–Australia plate boundary zone, South Island, New Zealand     

Timothy A. Little  Martha K. Savage  Basil Tikoff 《Geophysical Journal International》2002,151(1):106-116

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Attenuation of shear-waves in the back-arc region of the Hellenic arc for frequencies from 0.6 to 16 Hz     

Antonis Polatidis  Anastasia Kiratzi  Panagiotis Hatzidimitriou  Basil Margaris 《Tectonophysics》2003,367(1-2):29-40

Q_β for shear-waves is determined for the inner part of the Hellenic arc, the back-arc area, as a function of frequency in the range 0.6–16 Hz. We used 314 digital records from 32 earthquakes with magnitudes (M_w) ranging from 3.9 to 5.1. Epicentral distances ranged from 65 to 515 km. The data were obtained in 1997 during a 6-month operation of a digital portable network in Greece. The Q_β estimates were made for five frequency bands centred at 0.8, 1.5, 3.0, 6.0 and 12.0 Hz and the Q_β values obtained were 47, 79, 143, 271 and 553, respectively. The results show that Q_β for S-waves increases with frequency taking the form Q_β=55f ^0.91 (or Q_β⁻¹0.018f^−0.91). The high attenuation and the strong frequency dependence found, which is close to the frequency dependence of coda Q for Greece, are characteristic of an area with high seismicity, rapid extension, and in agreement with other similar studies in Greece.  相似文献   

Fabric studies within the Cascade Lake shear zone, Sierra Nevada, California   总被引：1，自引：0，他引：1  

Basil Tikoff  Matthew R. Davis  Christian Teyssier  Michel de St. Blanquat  Guillaume Habert  Sven Morgan   《Tectonophysics》2005,400(1-4):209-226

The Cascade Lake shear zone occurs on the eastern margin of the Tuolumne Intrusive Suite, Sierra Nevada Batholith, California. Foliation in the zone is NNW trending and subvertical, and lineation is moderately south plunging. Deformation is syn-tectonic with emplacement of the Cathedral Peak granodiorite. A deformation gradient exists toward the NE margin of this pluton, with higher strains and lower temperatures of deformation found near the contact. We compare fabric data collected very densely in this shear zone using several techniques: field fabrics, 3D orientation of K-feldspar megacrysts, and AMS (anisotropy of magnetic susceptibility) analysis. In general, the results from the three different methods are in agreement. Deformation in this shear zone is part of a larger pattern of deformation within the Cathedral Peak granodiorite, as recorded by AMS analysis, and dextral shearing associated within the last stage of plutonism within the Sierra Nevada magmatic arc.  相似文献   

Temporal variations in bedload transport rates associated with the migration of bedforms     

Basil Gomez  Richard L. Naff  David W. Hubbell 《地球表面变化过程与地形》1989,14(2):135-156

Temporal variations in bedload transport rates that occur at a variety of timescales, even under steady flow conditions, are accepted as an inherent component of the bedload transport process. Rarely, however, has the cause of such variations been explained clearly. We consider three data sets, obtained from laboratory experiments, that refer to measurements of bedload transport made with continuously recording bedload traps. Each data set is characterized by a predominant low-frequency oscillation, on which additional higher-frequency oscillations generally are superimposed. The period of these oscillations, as isolated through the use of spectral analysts, ranged between 0·47 and 168 minutes, and was associated unequivocally with the migration of bedforms such as ripples, dunes, and bars. The extent to which such oscillatory behaviour may be recognized in a data set depends on the duration of sampling and the length of the sampling time, with respect to the period of a given bedform. Several theoretical probability distribution functions have been developed to describe the frequency distributions of (relative) bedload transport rates that are associated with the migration of bedforms (Einstein, 1937b; Hamamori, 1962; Carey and Hubbell, 1986). These distribution functions were derived without reference to a sampling interval. We present a modification of Hamamori's (1962) probability distribution function, generated by Monte Carlo simulation, which permits one to specify the sampling interval, in relation to the length of a bedform. Comparisons between the simulated and observed frequency distributions, that were undertaken on the basis of the data described herein, are good (significant at the 90 per cent confidence level). Finally, the implications that temporal variability, which is associated with the migration of bedforms, have for the accurate determination of bedload transport rates are considered.  相似文献