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801.
Since one does not know the photometric functions of various parts of Io, one cannot convert the observed geometric albedo of the satellite to a parameter more directly measurable in the laboratory. One must therefore convert laboratory reflectances to geometric albedos before quantitative comparisons between Io's surface and a laboratory sample are made. This procedure involves determining the wavelength dependence of the sample's photometric function. For substances such as sulfur, whose reflectance varies strongly with wavelength, it is incorrect to assume that the photometric function, and hence the ratio (laboratory reflectance/geometric albedo) is independent of wavelength. To illustrate this point, measurements of the color dependence of this ratio for sulfur are presented for the specific case in which the measured laboratory reflectance is the sample's normal reflectance. In general, unless the laboratory reflectance is precisely the geometric albedo, a wavelength-dependent correction factor must be determined before the laboratory sample can be compared quantitatively with Io's surface. 相似文献
802.
Possible interrelationships of different observations have been studied to clear up some obvious inconsistencies and develop a coherent picture of the kinematics of the Venus atmosphere. There is a wind shear in the vicinity of 60 km with vertical dimensions on the order of a scale height. The kinematical model has negligible surface winds, speeds increasing with altitude to approximately 45 km, a layer of high-speed retrograde zonal winds extending from approximately 45 to 60 km, a wind shear between 60 and 65 km, and slow atmospheric motions above this. Spacecraft data show that the region of high-speed winds is thicker on the day side of the planet than on the night side. 相似文献
803.
The energetics of a current sheet that forms between newly emerging flux and an ambient field are considered. As more and more flux emerges, so the sheet rises in the solar atmosphere. The various contributions to the thermal energy balance in the sheet are approximated and the resulting equation solved for the internal temperature of the sheet. It is found that, for certain choices of the ambient magnetic field strength and velocity, the internal temperature increases until, when the sheet reaches some critical height, no neighbouring equilibrium state exists. The temperature then increases rapidly, seeking a hotter branch of the solution curve. During this dynamic heating, the threshold temperature for the onset of plasma microinstabilities may be attained. It is suggested that this may be a suitable trigger mechanism for the recently proposed emerging flux model of a solar flare.This work was done while the author was participating in the CECAM workshop on Plasma Physics applied to Active Solar Phenomena, August–September 1976 at Orsay, France, and the Skylab Solar Workshop on Solar Flares (sponsored by NASA and NSF and managed by the High Altitude Observatory). 相似文献
804.
David F. Webb Patrick S. MciIntosh Jerome T. Nolte Craig V. Solodyna 《Solar physics》1978,58(2):389-396
The positions of X-ray coronal transients outside of active regions observed during Skylab were superposed on H synoptic charts and coronal hole boundaries for seven solar rotations. We confirmed a detailed spatial association between the transients and neutral lines. We found that most of the transients were related to large-scale changes in coronal hole area and tended to occur on the borders of evolving equatorial holes.Skylab Solar Workshop Post-Doctoral Appointee, 1975–1977. 相似文献
805.
T. A. Heppenheimer 《Celestial Mechanics and Dynamical Astronomy》1976,14(2):175-200
We consider a restricted six-body problem, consisting of Jupiter, the four Galilean satellites, and an orbiter. The Galilean satellites' orbits are circular and coplanar; Io, Europa, and Ganymede are in exact resonance; their mean longitudes obey the Laplace relation. We seek periodic orbits which avoid close approaches to any satellite; such orbits are of interest for mission planning. They are approximated as equilibrium points of sets of variational equations associated with time-averaged disturbing functions. Stability of the solutions is also determined. The orbits of greatest interest are:Planar: twice Callisto's period, eccentricity0.6Planar: four times Callisto's period, eccentricity0.75Slightly inclined: twice Callisto's period, eccentricity arbitraryPlanar: 4/5 or 5/4 Europa's period. 相似文献
806.
807.
T. P. Armstrong S. M. Krimigis D. Hovestadt B. Klecker G. Gloeckler 《Solar physics》1976,49(2):395-407
Comprehensive measurements of the temporal variations of the Z 6 charge composition in the 4 July 1974 solar event made with experiments aboard IMP-7 and 8 show that large variations in the charge composition occur in three-hour-averaged intensities. Hourly averaged fluxes show variations as large as factors of 3 to 4 from one hour to the next and 3 hour averages show nearly a factor of 10 peak to minimum over the event. The precision of the measurements are limited by counting statistics of the Fe-group channel. Iron to oxygen variations are established by both rate channel and pulse height analysis techniques. Comparison of measurements from IMP-7 and 8, separated by about 70 R
E shows that, while significant differences in composition and intensity exist for brief periods, the gross compositional variations are reproduced well at both spacecraft. These observations provide particularly stringent conditions for theories of the acceleration, release, and propagation of solar energetic particles. 相似文献
808.
Model ionospheres are calculated for Saturn, Uranus, and Neptune. Protons are the major ions above 150 km altitude measured from a reference level where the hydrogen density is 1 × 1016 molecules cm?3, while below 150 km quick conversion of protons to H3+ ions by a three-body association mechanism leads to a rapid removal of ionization in dissociative recombination of H3+. Electron density maxima are found at about 260 km for Saturn and Uranus and 200 km for Neptune. Present knowledge of the physical and chemical processes in the atmospheres of these planets suggests that their ionospheres probably will not be Jupiter-like. 相似文献
809.
A.J. Kliore G. Fjeldbo B.L. Seidel D.N. Sweetnam T.T. Sesplaukis P.M. Woiceshyn S.I. Rasool 《Icarus》1975,24(4):407-410
The occultation of the Pioneer 10 spacecraft by Io (JI) provided an opportunity to obtain two S-band radio occultation measurements of its atmosphere. The dayside entry measurements revealed an ionosphere having a peak density of about 6 × 104 elcm?3 at an altitude of about 100 km. The topside scale height indicates a plasma temperature of about 406 K if it is composed of Na+ and 495 K if N2+ is principal ion. A thinner and less dense ionosphere was observed on the exit (night side), having a peak density of 9 × 103 elcm?3 at an altitude of 50 km. The topside plasma temperature is 160 K for N2? and 131 K for Na+. If the ionosphere is produced by photoionization in a manner analogous to the ionospheres of the terrestrial planets, the density of neutral particles at the surface of Io is less than 1011?1012 cm3, corresponding to a surface pressure of less than 10?8 to 10?9 bars. Two measurements of its radius were also obtained yielding a value of 1830 km for the entry and 192 km for the exit. The discrepancy between these values may indicate an ephemeris uncertainty of about 45 km. The two measurements yield an average radius of 1875 km, which is not in agreement with the results of the Beta Scorpii stellar occultation. 相似文献
810.
Cinematographic observations of solar prominences made at Mauna Loa during the past couple of years suggest that there is a well-defined sub-class of ascending prominences characterized by closed-system transference of chromospheric material along an arch or loop (up one leg and down the other); meanwhile the entire prominence envelope steadily rises upward and expands through the corona. We denote these prominences as fountains. Several examples are described. Fountains appear to be well contained by coronal magnetic fields. Their total kinetic energy is in the order of 1030 erg but dissipation is typically quite slow (over time periods like 100 min) so that the correlative disturbances (radio bursts, coronal transients, chromopsheric brightenings, etc.) are generally unspectacular or non-existent.This research was started when E. T.-H. was still on the staff of the High Altitude Observatory.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献