摘要:

New far ultraviolet spectra of Jupiter with a significant improvement in sensitivity and spectral resolution have been obtained from a sounding rocket by using a 10‐channel spectrometer behind a pointing telescope. The major results obtained from these spectra are (1) a new measurement of the Jovian H I λ 1216‐Å brightness (a comparison with other measurements indicates that the Ly α emission is likely to be variable), (2) the measurement of the wavelength‐dependent albedo for Rayleigh scattered solar radiation from ∼1550 to 1875 Å with ∼25‐Å resolution making it possible to set new upper limits on the abundances of some of the minor constituents in the upper Jovian atmosphere, and (3) a demonstration that weak emissions between ∼1250 and ∼1500 Å and near 1600 Å are probably the Lyman bands of H2excited b

ISSN:0148-0227    

DOI:10.1029/JA081i034p05797

年代:1976

数据来源: WILEY

摘要:

A detailed extensive analysis is made of the solar particle propagation during the long‐lasting, complicated November 18, 1968, solar flare event. A thorough analysis is made of the propagation, taking into account (1) the effect of large‐scale interplanetary magnetic field (IMF) disturbances on particle populations, (2) the role of long‐lasting solar injection processes, (3) small‐angle scatterings in the IMF within 1 AU, (4) the influence of a distant (>1 AU) scattering barrier, and (5) the particle abundance ratios. It is concluded that the solar cosmic rays were the result of a long‐lasting solar injection process, the length of the injection increasing for lower‐energy particles. The pitch angle propagation characteristics of these particles can be explained by particle propagation in a medium with a long mean free path (≈0.3 AU). It is suggested that the techniques of this analysis and the basic conclusions are applicable to many other nondiffusive appearing solar pa

ISSN:0148-0227    

DOI:10.1029/JA081i034p05807

年代:1976

数据来源: WILEY

摘要:

Ionospheric plasma, driven into motion by the magnetospheric convection electric field, interacts with the neutral upper atmosphere via collisions. These collisions provide both a momentum source (ion drag) and an energy source (Joule heating) for the neutral atmosphere. A three‐dimensional numerical model has been used to investigate the dynamical effects of this interaction on the neutral upper atmosphere. The effects of Joule heating, of the redistribution of heat input by global horizontal winds, and of adiabatic heating and cooling associated with vertical motions all depend on the neutral wind velocity. Thus the coupled set of neutral hydrodynamic and ion mobility equations is solved self‐consistently in order to determine the global neutral density, temperature, and wind fields simultaneously. These calculations indicate that notable effects on the characteristics of the neutral upper atmosphere are caused by this interaction. The Joule heating rate, although small at low latitudes, increases strongly with latitude Λ up to Λ ∼70° and becomes comparable to that due to EUV absorption there. Joule heating also provides a heat source at night, whereas EUV heating provides none. Thermospheric temperatures and densities rise in response to the additional heating caused by ion‐neutral collisions. The thermospheric wind fields are affected in two ways by magnetospheric convection. Joule heating causes a general equatorward flow which opposes the daytime poleward and the nighttime equatorward flow caused by EUV heating. Ion drag, on the other hand, causes an increase in the neutral poleward motion during the day and an equatorward motion at night. Thus the combined effects of ion drag and Joule heating lead to a substantial increase in the nighttime neutral meridional velocity; the effect during the day depends on the relative size of the effects of ion drag and Joule heating. These results emphasize the importance of the interaction among the magnetosphere, the ionosphere, and the neutral upper

ISSN:0148-0227    

DOI:10.1029/JA081i034p05822

年代:1976

数据来源: WILEY

摘要:

The large‐scale gradient in the bulk velocity of the solar wind, previously inferred from a study of large numbers of solar wind measurements made at two widely separated locations by Mariner 5 and the near‐earth Explorers 33, 34, and 35 during mid‐1967, is interpreted to be a heliographic latitude gradient. Nearly 2000 differences in hourly averages of the solar wind velocity observed at the two locations, after being corrected for differences in solar longitude, are analyzed by using a technique previously applied to the propagation of sector boundaries between Mariner 5 and earth. The higher velocities at the higher‐latitude Explorers, as compared with those observed at the lower‐latitude Mariner 5, imply a latitude gradient of roughly 15 km/s/deg. This value for the gradient is in excellent agreement with that obtained previously from the study of sector boundaries. A simple model of the velocity‐latitude dependence is developed to illustrate that the observed relationship between the velocities at Mariner and the Explorers, (VM‐ 275) = 11 + 0.76(VE‐ 275), is consistent with this gradient and with the latitude separation of the spacecraft. Further evidence of a latitude gradient is obtained by analyzing separately the velocities at the Explorers and at Mariner 5 as functions of latitude. This technique yields essentially the same relation between velocity and latitude as the multispacecraft analysis. The Vela 2, 3, and 4 solar rotation velocity averages observed near earth from 1964 through 1967 (interpreted by Hundhausen et al. (1971) as being due to a latitude gradient) are combined with solar rotation averages of the Mariner and Explorer data and then analyzed as a function of latitude to obtain a long‐term value for the gradient. These single‐location analyses consistently yield latitude gradients in the northern hemisphere below 7¼° that range between 10 and 15 km/s/deg. Interplanetary scintillation estimates of the solar wind velocity, obtained in 1972 and 1973, are also analyzed and yield a somewhat smaller latitude gradient of 4–6 km/s/deg. The latter values provide evidence of the existence of the gradient at higher

ISSN:0148-0227    

DOI:10.1029/JA081i034p05833

年代:1976

数据来源: WILEY

摘要:

It is argued that the interplanetary magnetic field cannot be simply considered as consisting of small short‐scale resonant fluctuations superposed on the long‐term average spiral field if one wants to calculate the average transport properties of galactic cosmic rays. The interest is focused on pitch angle diffusion, where the relevant average field varies strongly on a medium scale exceeding the magnetic correlation length. This leads to an average Fokker‐Planck equation for the average galactic intensity. Direct reflections and large‐scale drift effects that may play a role on the same scale are not considered. When the interplanetary medium is assumed to be statistically axisymmetric, an average spatial diffusion coefficient is derived from the above Fokker‐Planck equation and compared with the Pioneer 10 and 11 radial intensity gradients as obtained by the Chicago group. The medium‐scale variations also introduce a solar cycle variation of the diffusion coefficient from which a corresponding variation of the galactic intensity is estimated. Quantitatively, the resulting solar cycle variation appears to be only of marginally sufficient strength. This may not be too surprising, since changes in magnetic field topology, drift effects, and direct particle reflections have not been

ISSN:0148-0227    

DOI:10.1029/JA081i034p05841

年代:1976

数据来源: WILEY

摘要:

Field‐aligned currents, which are known to play an important role in the dynamics of the earth's magnetosphere, would also be expected to flow in the Jovian magnetosphere during magnetically active periods. Such currents are difficult to observe largely because of their limited spatial extent and intermittent nature, but on the Pioneer 11 inbound pass to Jupiter on day 336, 1800 GRT, near theLshell of Ganymede, the helium vector magnetometer recorded a structured perturbation with the characteristic signature of a field‐aligned current. No analogous structure was found on a similar Pioneer 10 inbound pass (day 337, 1200 GRT). The perturbation could have been caused by turbulence within the wake of Ganymede through which the spacecraft was moving or the perturbation could represent the first observation of a Jovian substorm. The observations are discussed in terms of both models, and difficulties are exami

ISSN:0148-0227    

DOI:10.1029/JA081i034p05853

年代:1976

数据来源: WILEY

摘要:

Intensive correlative studies of magnetic fields and plasmas within the earth's magnetotail at geocentric radial distances of ∼23–46REduring March‐October 1974 have revealed striking new features. The instruments employed in this survey were the University of Iowa Lepedea and the Goddard Space Flight Center magnetometer. The hot tenuous plasmas within the plasma sheet were found to be in a state of almost continual flow and were threaded with northward, or closed, geomagnetic field lines. The magnetic field is referred to as ‘northward’ or ‘southward’ if the componentBzis positive or negative, respectively, regardless of the magnitudes of the other components. Proton bulk speeds were in the range 50–500 km s−1. The magnetic fields are directed northward, irrespective of whether the plasma flows are tailward or earthward. These observations show the demand for a strong persistent source of magnetic flux and hot plasmas for the plasma sheet. No characteristic proton bulk flows, e.g., strong dawn‐to‐dusk motions, were evident during crossings of the magnetic neutral sheet. Occasionally, the satellite encountered the region of acceleration in the magnetotail, the ‘fireball.’ This spectacular phenomenon exhibits strong jetting of plasmas in excess of 1000 km s−1, proton temperatures of ∼107°K (kT∼ 1 keV), disordered magnetic fields, southward magnetic fields during tailward jetting of plasmas, and northward magnetic fields for fast plasma flows toward earth. Observations of electrons are used to demonstrate that earthward plasma flows within the fireball are threaded with closed geomagnetic field lines, and open magnetic field lines are embedded in the tailward jetting plasmas. The magnetosheathlike plasmas within the boundary layers which are positioned contiguously to the plasma sheet display striking evidences of plasma heating, great changes in bulk flow velocities and acceleration of energetic electrons withE>45 keV. Typical temperatures and bulk flow speeds within the boundary layer plasmas are ∼106°K and ∼400 km s−1, respectively. Persistent zones of southward magnetic fields are detected, which are often positioned adjacent to the plasma sheet and within the boundary layer plasmas. Rotations of the magnetic fields from southward to northward, or vice versa, in these boundary layers are accompanied by large enhancements of energetic electron intensities, substantial heating of the low‐energy electron distributions, and strong perturbations of the proton velocity distribution functions. During periods for northward directed fields the proton bulk flows decelerate to speeds of ≲200 km s−1, densities decrease, and the proton velocity distributions can be fitted with two Maxwellians with temperatures of ∼2 × 105°K and ∼ 107to 5 × 107°K for specific examples. The boundary layer plasmas appear to be the primal source of hot plasmas and closed geomagnetic field lines for the plasma sheet. Qualitatively, all of the major results of the present study are consistent with macroscopic features which are expected from merging of magnetic field lines in the earth's magnetotail or, more specific

ISSN:0148-0227    

DOI:10.1029/JA081i034p05859

年代:1976

数据来源: WILEY

摘要:

A magnetic pulsation index based on the periods of Pc 2–4 pulsations as recorded in earth current measurements at the Borok Geophysical Observatory has been claimed to be a measure of the interplanetary field. Tests of this index for the period 1972 to June 1974 show only a 27% success rate. However, a simple recalibration of the index improves the success rate to 51%. The success of the index indicates that the source of many terrestrial magnetic pulsations is external to the magnetospher

ISSN:0148-0227    

DOI:10.1029/JA081i034p05882

年代:1976

数据来源: WILEY

摘要:

We investigate the cosmic ray radial diffusion coefficient resulting from linearly polarized Alfvén waves propagating outward through an azimuthally structured solar wind. The analysis utilizes a diffusion coefficient derived from quasi‐linear Fokker‐Planck theory and a model solar wind stream in which the solar wind velocity varies linearly with azimuth. It is found that beyond 1 AU the stream significantly reduces the diffusion coefficient below that for a spherically symmetric solar wind. The diffusion coefficient is also found to reach a minimum value at a heliocentric distance of approximately 75Rs, and this minimum moves outward with increasing steepness of the wave spectrum. The diffusion coefficient is a separable function of radius and rigidity below approximately 0.5 GV, but at higher rigidities it is found that the separability fails. Finally, it is concluded that the present diffusion theory is consistent with a cosmic ray gradient which decreases slowly withrand has a mean value, between 1 and 5 AU, of about 3%/AU for 1‐GeV galactic p

ISSN:0148-0227    

DOI:10.1029/JA081i034p05887

年代:1976

数据来源: WILEY

摘要:

The topic of the whistler precursor, a discrete VLF emission which is occasionally observed to precede a whistler, is briefly reviewed. An analysis of some observations of precursors is presented, and two new mechanisms for the generation of precursors are described. It is shown that a mechanism in which two frequency components of a whistler, having the same group delay, interact to trigger a precursor at the difference of the frequencies does not predict results which agree well with observations. A mechanism in which part of the energy from the causative lightning stroke travels in an unducted mode, undergoing one magnetospheric reflection and refraction from the inner edge of the plasmapause, arriving in the equatorial plane with its wave vector parallel to the geomagnetic field, predicts results which are in good agreement with experimental observations. This method is compared with the model of Dowden (1972).

ISSN:0148-0227    

DOI:10.1029/JA081i034p05900

年代:1976

数据来源: WILEY