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Emission gradient curves for extreme ultraviolet (EUV) resonance lines of O VI and Mg X have been constructed from spectroheliograms of quiet limb regions observed with the Harvard experiment on Skylab. An analysis of these data suggests that the coronal temperature rises throughout the height range 1.03-1.3 solar radii. This result implies that in quiet regions there is significant coronal heating beyond 1.3 solar radii.
A model for the formation and confinement of dense (at least about 1 billion per cu cm) clouds in QSOs and active galactic nuclei is presented wherein thermal instabilities behind radiative shocks cause the collapse of regions where the preshock density is enhanced over that of the surrounding medium. Such shocks (of total energy around 10 to the 51st ergs) are likely to occur if the frequent optical outbursts observed in many of these objects are accompanied by mass ejections of comparable energy. It is found that clouds quite similar to those thought to exist in QSOs etc. can be created in this manner at radii of the order of 10 to the 17th cm. The clouds can be subsequently accelerated to observed bulk velocities by either radiation pressure or a collision with a much stronger (total energy around 10 to the 53 ergs) shock. Alternatively, their high observed velocities could be caused by gravitational infall or rotation. The mass production required at inner radii by the outflow models can be supplied through a mechanism previously discussed by Shields (1977).
During a period of several days when the solar wind was relatively quiet, the magnetotail boundary near lunar distance swept back and forth past Explorer 33 as the spacecraft traveled through a distance perpendicular to the earth-sun line of about 17 earth radii. The boundary crossings are remarkably well-correlated with peaks in the AE index, even though the magnitudes of the peaks are only on the order of 200 nT. Examination of the regions of multiple crossings on other Explorer 33 and 35 orbits reveals that they commonly cover large distances perpendicular to the earth-sun line, although correlation with AE is often obscured, probably by external solar wind conditions. It is concluded that a substantial fraction of the scatter in published statistical plots of boundary crossing positions can be accounted for in terms of an internal substorm-related motion with an amplitude of 5-8 earth radii. The data suggest that the motion takes the form of a compressional deformation wave convecting down the tail.
Measurements of the effect of dayside magnetic reconnection on the position of the earth's forward magnetopause have been scaled to Mercury in order to predict the mean solar wind stand-off distance for average conditions of solar wind dynamic pressure. It is found that for a significant portion of the time Mercury's magnetopause will be eroded and/or compressed to within 0.2 Mercury radii of the planet's surface. Solar wind stand-off distances and solar wind dynamic pressures are also calculated for the two Mariner 10 encounters with Mercury's magnetosphere. Values of the solar wind stand-off distance range from 1.3 to 2.1 Mercury radii.
Extensive measurements of low-energy positive ions and electrons were made throughout the Jupiter encounter of Voyager 1. The bow shock and magnetopause were crossed several times at distances consistent with variations in the upstream solar wind pressure measured on Voyager 2. During the inbound pass, the number density increased by six orders of magnitude between the innermost magnetopause crossing at approximately 47 Jupiter radii and near closest approach at approximately 5 Jupiter radii; the plasma flow during this period was predominately in the direction of corotation. Marked increases in number density were observed twice per planetary rotation, near the magnetic equator. Jupiterward of the Io plasma torus, a cold, corotating plasma was observed and the energy/charge spectra show well-resolved, heavy-ion peaks at mass-to-charge ratios equal to 8, 16, 32, and 64.
The International Sun-Earth Explorer (ISEE) spacecraft 1 and 2 carry receivers for detecting electromagnetic waves with kilometric wavelengths. For selected receiver frequencies from 30 kHz to 2 MHz, a 10-kHz bandwidth channel is single-sideband mixed down to baseband. These analog data and a reference frequency, which is a submultiple of the local oscillator frequency, are transmitted to ground stations and tape recorded along with the precise time and frequency information. Cross correlation of these tape recorded signals constitutes a satellite-to-satellite interferometer with a fringe spacing of 0.4 to 41 arcmin (at a range of 10,000 to 100 km spacing between spacecraft for 250 kHz in frequency) and with a time-delay resolution of 32 microsec for a 10-kHz bandwidth, which gives an angular resolution of 3 min to 6 deg of arc. For kilometric radiation at earth, sources in the size range of 25 to 2500 km can be identified (from 20 earth radii) and located in relative position ranging from 0.02 to 2 earth radii, depending on spacecraft spacing. Reception and analysis of solar and Jovian bursts may also be possible.
Model atmosphere calculations are used to assess whether an empirically derived relation between V-R and surface brightness is independent of a variety of stellar paramters, including surface gravity. This relationship is used in a variety of applications, including the determination of the distances of Cepheid variables using a method based on the Beade-Wesselink method. It is concluded that the use of a main sequence relation between V-R color and surface brightness in determining radii of giant stars is subject to systematic errors that are smaller than 10% in the determination of a radius or distance for temperature cooler than 12,000 K. The error in white dwarf radii determined from a main sequence color surface brightness relation is roughly 10%.
The magnitude of the strong flow of 1.79-2.15 MeV protons away from the Jovian magnetic equator is used to estimate the residence lifetimes of these protons in the equatorial source region. The lifetime is approximately 1.2 x 10 to the 5th/(R - 5.8)-squared sec, where R is distance in Jovian radii from Jupiter's center to the equatorial region of interest. At Europa and Ganymede (but not at Io) this lifetime is 1-2 orders of magnitude shorter than sweepup lifetimes by the moons. The fluxes of these protons, integrated over the observed range from 6 to 40 Jovian radii, amount to 3 x 10 to the 23rd particles per second, per degree of longitude and carry away about 9 x 10 to the 17th ergs per second per degree.
Observations of particle structures by a medium-energy particle experiment on the ISEE 1 and 2 spacecraft at a distance of about 20 earth radii in the geomagnetic tail are presented. Comparison of these data with plasma data indicates the existence of a layer of energetic electrons and ions just outside the plasma sheet. The region outside the plasma sheet in the high-latitude lobe is permeated with low-intensity low-energy (about 1.5 KeV) ions. These particle structures have velocities of a few kilometers per second to at least about 60 km/s. Large-scale motions are observed with onset and recovery of substorms. The dimensions of the particle structures are estimated to range from about 200 to 10,000 km at 20 earth radii. The particle structures are dependent upon the energy as well as the species of the particles.
The solar wind and IMF data obtained by the Venus probe Mariner 5 (at a distance of 460 earth radii) and by the earthbound Explorer 34 satellite, on June 24, 25, and 26, 1967 were examined. It is demonstrated that the occurrence and intensity of magnetospheric substorms can be predicted about 1-3 hours prior to their onsets by monitoring the energy coupling function at a distance of a few hundred earth radii upstream of the solar wind. It appears that the 'epsilon signal' propagates with different speeds, perhaps depending on the propagation time of disturbances which increase epsilon.
The effect of gravitational redshift on the blackbody radii, as deduced from the tails of X-ray bursts, is considered. Observed values of blackbody radii put an upper limit to the mass and constrain the mass-radius relations of neutron stars. Possible consequences for the equation of state of high-density matter are briefly discussed.
The paper presents approximate solutions obtained for a radiative transfer problem that represents a highly-idealized description of the multiple scattering of solar resonance radiation in the nearby interstellar medium. The problem of a point source in the center of a spherically symmetric cavity imbedded in an infinite uniform medium is solved for a range of cavity radii. First and second-order scattering contributions are calculated, and the Eddington approximation is used to estimate the higher order components of the radiation field. It is shown that for coherent scattering at very large cavity radii, the backscattered intensity from the cavity approaches three times the value deduced from the optically thin solution, in agreement with previous work. It is concluded that an accurate analysis of sky background will require including not only the frequency redistribution, but also the correct spatial distribution of density.
Results of Pioneer Saturn vector helium magnetometer measurements of the magnetic field and magnetosphere of Saturn are reported. The detection of a bow shock at 23.7 Saturn radii and the magnetosphere crossing at 17.4 Saturn radii suggest an equatorial surface field of 0.3 gauss, which is similar to that of the earth, and the polarity of the field is observed to be similar to that of Jupiter and opposite to the earth's. An increase of magnetic field strength with decreasing radius indicates the dipole nature of the magnetic field, which modified by the compression of the magnetosphere by the solar wind and the presence of a ring current in the middle magnetosphere. Inversions of the field measurements to obtain equivalent dipole source vectors reveal that the tilt angle between the magnetic dipole and the rotation axis is less than 1 deg, and spherical harmonic analysis of the data indicates that the magnetic field is more uniform than those of the earth and Jupiter, consistent with a small Saturn core. An apparent hydromagnetic wake associated with Titan was also observed.
Several interesting cloud and atmospheric features of the Saturn system have been observed by the long-wavelength channel of the two-channel ultraviolet photometer aboard the Pioneer Saturn spacecraft. Reported are observations of the most obvious features, including a Titan-associated cloud, a ring cloud, and the variation of atmospheric emission across Saturn's disk. The long-wavelength data for Titan suggest that a cloud of atomic hydrogen extends at least 5 Saturn radii along its orbit and about 1.5 Saturn radii vertically. A ring cloud, thought to be atomic hydrogen, has also been observed by the long-wavelength channel of the photometer; it shows significant enhancement in the vicinity of the B ring. Finally, spatially resolved observations of Saturn's disk show significant latitudinal variation. Possible explanations of the variation include aurora or limb brightening.
The origin of the newly discovered narrow ring systems around Jupiter, Saturn and Uranus is considered. It is pointed out that both the Uranian and Jovian ring systems have mean orbital radii of 1.8 planetary radii and lie within the Roche zones of their respective planets, and it is suggested that the Jovian ring is the product of the disintegration of a satellite that entered the Roche zone, and that large numbers of small particles are now in horseshoe orbits about the Lagrangian equilibrium points of the remnant chunks. Analysis of the path of a ring particle in a horseshoe orbit is shown to result in ring structures in agreement with those observed for the circular rings of Jupiter and the highly eccentric ring of Uranus. The stability of these ring systems is then considered, and it is suggested that the F ring of Saturn, which lies outside the Roche zone, represents primordial matter not yet accreted by small satellites just inside the Mimas first-order resonances.
Upper tropospheric temperature anomalies are detected in brightness temperature data from the Nimbus 6 Scanning Microwave Spectrometer (SCAMS). Brightness temperature anomalies are related to surface pressure anomalies through the radiative transfer and hydrostatic equation. Surface wind speeds at outer radii are then estimated using the gradient wind equation and a shearing parameter. The method is first tested using simulated satellite data constructed from temperature, pressure and height data recorded by aircraft reconnaissance of four hurricanes. Wind speeds in the 80-95 kPa region are estimated with 2-3 m/sec accuracy. Next, 55.45 GHz SCAMS data over eight typhoons during 1975 are used to estimate the radii of 15.4 m/sec (30 kt) and 27.5 m/sec (50 kt) winds. Accuracies of about + or - 80 and + or - 70 km, respectively, are found. It is suggested that the technique be further tested using data from the Microwave Sounding Unit on board the TIROS-N and NOAA 6 satellites.
The variations with Jovian magnetic longitude observed in the intensity of the S II emission from the plasma torus surrounding Jupiter near the orbit of Io are investigated. Spectrographic observations of S II emission from 2.1 to 8.3 Jupiter radii from the planet obtained from 1976 to 1979 were examined to determine emission intensities in relation to position. The detected emission is found to be sharply confined to a magnetic latitude within 12 deg of the equator and a region inside 6.7 Jupiter radii, just outside of Io's orbit, with maximum emission at a magnetic longitude of 60 deg. The region of maximum brightness is observed to include the active centers for the currents expected in the flux tubes connected with Io, support of the magnetic anomaly models of Dressler and Hill (1979). Electron temperatures between 10 to the 3.92 and 10 to the 4.80, and densities of 10 to the 4.2/cu cm and a S II column abundance of 1.5 x 10 to the 13th/sq cm are estimated for the brightness region near the ansa of the emission torus. An order of magnitude difference between S II column abundances obtained in the present investigation and found by Brown (1978) is attributed to a change in sulfur content, possibly related to Ionian volcanic activity, while electron temperatures and densities are found to remain fairly constant.
IMP 7 observations of plasma sheet structure and dynamics made during a 24-h period in which the satellite traversed the tail plasma sheet at a radial distance of 35 earth radii and remained within 2 earth radii of the expected position at the neutral sheet and in which at least five substorms occured on the ground are presented. High-time-resolution measurements of the magnetic field, plasma flow and greater than 50-keV protons obtained by the satellite and ground-based magnetic measurements are discussed for a 4-hr interval in which two small substorms occurred, a 6-hr geomagnetically quiet interval in which moderate variable plasma flows were observed, a very rapid, smooth neutral sheet crossing and earthward plasma flow during the expansion phase of a small substorm, a moderate-size substorm in which a prolonged interval of field-aligned tailward flow commenced at onset, a strong tailward and dawnward flow burst in an interval between substorms and a large substorm in which strong tailward flow was observed. Observations indicate the significant distortion of the tail field, possibly by plasma flow stresses, a neutral sheet structure occasionally resembling the hydromagnetic rotational discontinuity and a high level of magnetic turbulence during an earthward plasma flow which may contribute towards plasma sheet dissipation.