Evidence for the depletion of ammonia in the Uranus atmosphere

The theoretical disk brightness temperature spectra for Uranus are computed and compared with the observed microwave spectrum. It is shown that the emission observed at short centimeter wavelengths originates deep below the region where ammonia would ordinarily begin to condense. We demonstrate that this result is inconsistent with a wide range of atmospheric models in which the partial pressure of NH₃ is given by the vapor-pressure equation in the upper atmosphere. It is estimated that the ammonia mixing ratio must be less than 10^?6 in the 150 to 200°K temperature range. This is two orders of magnitude less than the expected mixing ratio based on solar abundances. The evidence for this depletion and a possible explanation are discussed.     

Vertical extent of zonal winds on Venus

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.     

A trigger mechanism for the emerging flux model of solar flares

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).     

Evidence linking coronal transients to the evolution of coronal holes

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.     

Effects of charge exchange involving H and H+ in the upper atmosphere

It is argued that there is a terrestrial loss of hydrogen as ions which includes the polar wind but extends effectively down to a latitude in the range 45–50° invariant. In daytime and for much of the night-time the flux is close to the limiting value for H⁺ flow through the topside ionosphere. It is argued that the flux decreases rapidly with increasing solar activity, following the decrease in neutral hydrogen concentration. It has been found that as solar activity increases the Jeans escape flux increases, and the charge exchange escape flux increases until moderate solar activity levels are reached. As solar activity increases from moderate to high levels, the charge exchange escape may decrease again. A new budget for terrestrial hydrogen loss over the solar cycle is given. The global flux of hydrogen ions outward from the ionosphere is comparable with estimates of the plasma sheet loss rates, and this flux, together with some solar wind plasma, is an attractive source for the plasma sheet.The energetic neutrals produced from the charge exchange of ring current ions with thermal-energy neutrals in the exosphere produce the optical emission of the equatorial aurora, which can be related to ion production rates near and above the E-region. The ionization production is adequate to explain the enhancements in ion production observed during magnetic storms at Arecibo.     

Introduction to the restricted Jupiter orbiter problem

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.     

Observation of temporal and spatial variations in the Fe/O charge composition of the solar particle event of 4 July, 1974

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.     

Ionospheric models of Saturn,Uranus, and Neptune

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.