摘要:

Radio occultation data from the flybys of Pioneer 10 and 11 have been analyzed using a technique which accounts for the oblateness of Jupiter's atmosphere. The center of refraction is located by the radius of curvature and the normal at the closest approach point of the ray. An Abelian inversion of the data is then carried out holding the center of refraction fixed at some average value for each occultation event. Applying this approximate theory, for the three measurements described herein, the results are consistent, showing a temperature inversion between the 10 and 100 mb levels, with temperatures between 130 and 170° K at the 10 mb level and 80 to 120° K at 100 mb. These results are also in agreement with models for the temperature in the Jovian atmosphere derived from Pioneer 10 infrared radiometer data as well as those constructed from radiative‐convective balance calculations. Nevertheless, all results derived from radio occultation measurements of Jupiter are ultimately limited in their validity at the highest pressures by a lack of detailed knowledge of the shape of isobaric contours in Jupiter's atmosph

ISSN:0094-8276    

DOI:10.1029/GL003i003p00113

年代:1976

数据来源: WILEY

摘要:

Martian craters defined as fresh on the basis of morphologic parameters have been analyzed for the presence and abundance of various morphologic features as a function of size. Bowl‐shaped craters dominate the fresh crater population below about 15 km. The onset of central peaks occurs at about 5 km. Craters above about 15 km often have terraced walls, central peaks, and hummocky floors; at diameters of 40 km and greater, these features dominate fresh martian crater morphology. Central peak onset occurs at smaller diameters on Mars and the Moon than on Mercury, and terrace onset occurs at similar diameters on the Moon and Mars, but at larger diameters than on Mercury. Since Mars and Mercury have a similar surface gravitational acceleration (greater than twice that of the Moon), gravity‐controlled crater features should appear at similar diameters on the two planets. However, the differences in onset and abundances of central peaks and terraces on Mars and Mercury indicate that processes other than gravitational effects may also be import

ISSN:0094-8276    

DOI:10.1029/GL003i003p00117

年代:1976

数据来源: WILEY

摘要:

Crater populations on two major geologic units of Mercury have been classified into three morphologic types which characterize their state of degradation. The results indicate that one or more processes either prior to or contemporary with the formation of the 1300 km diameter Caloris Planitia reduced the population of fresh craters smaller than 70‐80 km diameter and totally erased the population of fresh craters smaller than 20‐30

ISSN:0094-8276    

DOI:10.1029/GL003i003p00121

年代:1976

数据来源: WILEY

摘要:

Re‐examination of the Venera‐4 magnetic field measurements at Venus encounter suggests that Venus may have an intrinsic magnetic dipole moment of about 6.5×1022Gauss‐cm³ which corresponds to a surface field of 30 gammas (1γ=10

ISSN:0094-8276    

DOI:10.1029/GL003i003p00125

年代:1976

数据来源: WILEY

摘要:

The daytime photoelectron energy spectrum has been measured at altitudes above 154 km by the photoelectron spectrometer experiment on the Atmosphere Explorer‐E satellite. Much higher energy resolution spectra than previous AE‐C results have been obtained. Below 200 km, well resolved peaks are observed in the spectrum corresponding to production of O+and N2+in various electronic states from photoionization of N2and O by solar He II (304A) radiation. Vibration‐rotation excitation of N2by inelastic electron scattering is observed at 2.5 eV. The features due to nitrogen disappear from the spectrum at altitudes above 2

ISSN:0094-8276    

DOI:10.1029/GL003i003p00129

年代:1976

数据来源: WILEY

摘要:

The first observations of a high energy ion shock spike extending in energy to>25 MeV for protons,>4.3 MeV/nuc for alpha particles, and>1.6 MeV/nuc for medium nuclei with Z ≥ 6 are reported. The measurements were obtained in the course of a solar particle event on September 15, 1974 by The Johns Hopkins University/Applied Physics Laboratory (JHU/APL) experiments on the IMP‐7 and IMP‐8 spacecraft. It is shown that the observations can be reasonably accounted for by intensive acceleration of charged particles at an "almost" perpendicular interplanetary shock wave. The data are inconsistent with a one‐step d.c.‐type acceleratio

ISSN:0094-8276    

DOI:10.1029/GL003i003p00133

年代:1976

数据来源: WILEY

摘要:

Interaction regions between adjacent solar wind streams have been identified between 1 and 5 AU using Pioneer 10 and 11 magnetic field and plasma measurements. Beyond 1 AU, a relatively large fraction of the interaction regions have been found to be accompanied by either forward shocks, reverse shocks, or shock pairs. The observations are consistent with previous theoretical proposals that the interaction between adjacent streams leads to the development of corotating interplanetary shocks.

ISSN:0094-8276    

DOI:10.1029/GL003i003p00137

年代:1976

数据来源: WILEY

摘要:

It is demonstrated that since fluctuations in the solar wind are not small, they can have important effects on the observed average values of parameters in the solar wind and their radial variation. The effect is distinct from the dynamical effect of waves and turbulence and results from the averaging process. It is concluded that, for example, the average density of the solar wind need not vary as 1/r², even if the average velocity is constant and radial. The effect on thermal anisotropies might also be important. The magnitudes of the effects depend on presently unknown correlations between fluctuations in the solar wind

ISSN:0094-8276    

DOI:10.1029/GL003i003p00141

年代:1976

数据来源: WILEY

摘要:

Sun‐aligned arcs are long and sometimes narrow optical structures which are oriented in the sun‐earth direction and which occur in the polar cap, generally during intervals of low magnetic activity. Their appearance, as seen by the DMSP and ISIS‐2 satellite photometers, is examined with respect to the north‐south orientation of the interplanetary magnetic field. In the DMSP pictures it is found that they appear when the IMF is directed northward. In 16 out of 18 unambiguous observations of sun‐aligned arcs by ISIS‐2, the IMF was directed northward; for the other two no IMF data was available. These results provide evidence for a strong correlation between the northward direction of the IMF and the occurrence of sun‐aligned arcs in the north

ISSN:0094-8276    

DOI:10.1029/GL003i003p00145

年代:1976

数据来源: WILEY

摘要:

The pitch‐angle distributions of 0.36 to 28.5 keV electrons in an inverted ‘V’ structure show characteristics that are consistent with an acceleration due to an electric field above an altitude of 750 km. The peak of the energy flux increases from Ep≈ 0.5 keV to Ep ≈ 10 keV and then decreases back to low energies over a 2° −3° latitude interval and thus gives an inverted ‘V’ appearance on an energy‐time spectrogram. As the energy (Ep) at the maximum energy flux increases, the reflected flux becomes essentially the same as the precipitated flux for E

ISSN:0094-8276    

DOI:10.1029/GL003i003p00149

年代:1976

数据来源: WILEY