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171.
172.
The July 12, 1973, occultation of Europa by Io was observed in 30 wavelength channels in the spectral region λλ3200-11, 000 Å with the 200-inch Hale telescope and a multichannel spectrometer. The data are presented in absolute units above the Earth's atmosphere. The data are analyzed to obtain the spectral reflectivity of seven localized areas on the disk of Europa centered on 324°W longitude. The equatorial material is confirmed to be darker than the eastward-skewed bright north polar cap and a hint is evident that the darker material as well may be somewhat redder than the cap material. 相似文献
173.
A model is presented which describes the 3-dimensional non-radial solar wind expansion between the Sun and the Earth in a specified magnetic field configuration subject to synoptically observed plasma properties at the coronal base. In this paper, the field is taken to be potential in the inner corona based upon the Mt. Wilson magnetograph observations and radial beyond a certain chosen surface. For plasma boundary conditions at the Sun, we use deconvoluted density profiles obtained from synopticK-coronameter brightness observations. The temperature is taken to be 2 × 106 K at the base of closed field lines and 1.6 x 106K at the base of open field lines. For a sample calculation, we employ data taken during the period of the 12 November 1966 eclipse. Although qualitative agreement with observations at 1 AU is obtained, important discrepancies emerge which are not apparent from spherically symmetric models or those models which do not incorporate actual observations in the lower corona. These discrepancies appear to be due to two primary difficulties - the rapid geometric divergence of the open field lines in the inner corona as well as the breakdown in the validity of the Spitzer heat conduction formula even closer to the Sun than predicted by radial flow models. These two effects combine to produce conductively dominated solutions and lower velocities, densities, and field strengths at the Earth than those observed. The traditional difficulty in solar wind theory in that unrealistically small densities must be assumed at the coronal base in order to obtain observed densities at 1 AU is more than compensated for here by the rapid divergence of field lines in the inner corona. For these base conditions, the value ofβ(ratio of gas pressure to magnetic pressure) is shown to be significantly greater than one over most of the lower corona - suggesting that, for the coronal boundary conditions used here, the use of a potential or force-free magnetic field configuration may not be justified. The calculations of this paper point to the directions where future research on solar-interplanetary modelling should receive priority:
- better models for the coronal magnetic field structure
- improved understanding of the thermal conductivity relevant for the solar wind plasma.
174.
We have analysed the variations of inclination in 13 satellite orbits as they pass slowly, under the action of air drag, through 15th-order resonance with the geopotential, when successive equatorial crossings are 24° apart and the ground track repeats after 15 rev. The size and form of the change in inclination are determined mainly by the values of the geopotential harmonics of 15th order and odd degree, and (with l = 15, 17, 19, …) in the usual notation. Our analysis gives values of these coefficients up to l = 33 as follows:
l | 109C?l,15 | 109S?l,15 |
15 | ?23.5 ± 0.8 | ?7.7 ± 0.8 |
17 | 6.3 ± 1.5 | 5.6 ± 1.5 |
19 | ?25.1 ± 2.5 | ?7.3 ± 2.3 |
21 | 27.8 ± 3.6 | ?0.7 ± 3.4 |
23 | 17.1 ± 4.1 | 13.9 ± 4.8 |
25 | ?1.1 ± 3.0 | 8.5 ± 4.2 |
27 | 10.0 ± 3.3 | 6.7 ± 2.7 |
29 | ?9.4 ± 3.5 | 0.1 ± 4.7 |
31 | 10.1 ± 5.4 | 3.8 ± 5.6 |
33 | 1.1 ± 5.7 | 3.1 ± 5.8 |