摘要:

In this paper we present Doppler velocity maps of the diffuse radar aurora obtained at 398 MHz with a backscatter radar located at Homer, Alaska. From the spatial distribution of Doppler velocities, we show that (1) the auroral echoes are definitely produced by scatter from wavelike fluctuations in the electron density such as those generated by a plasma instability; (2) the plasma instability is intimately associated with the electron‐ion streaming velocity; (3) the Doppler velocity appears to be dependent on the magnetic aspect angle; and (4) the Doppler velocity characteristics are, at least qualitatively, consistent with a quasi‐linear plasma instability model developed by Sudan et al. (19

ISSN:0148-0227    

DOI:10.1029/JA081i004p00425

年代:1976

数据来源: WILEY

摘要:

The intensity of solar radiation in 10‐Å intervals in the wavelength region 1230–1940 Å is presented, based on measurements with a rocket spectrometer flown twice, on November 2, 1973, and again on April 23, 1974. The estimated errors in the fluxes are ±20%. The fluxes are compared with measurements of others and are shown to be in good agreement with those of Parkinson and Reeves reported in 1969. The present data are used to compute the O2photodissociation coefficient as a function of the O2column d

ISSN:0148-0227    

DOI:10.1029/JA081i004p00436

年代:1976

数据来源: WILEY

摘要:

The proton, alpha particle, and electron fluxes measured following two west limb solar flare events are analyzed by using numerical solutions to the complete particle transport equation, including considerations of particle convection and energy loss. The values of the obtained mean free paths λrsuggest that interplanetary propagation conditions were different during these two events. During the November 4, 1968, event the derived values of λrwere ∼0.2–0.3 AU, while during the November 1969 event the derived values of λrwere ∼0.1 AU for particles with energies as low as a few MeV. For these events the rise and decay of the alpha and proton flux profiles can be reasonably reproduced with a distant (10 AU) free escape

ISSN:0148-0227    

DOI:10.1029/JA081i004p00441

年代:1976

数据来源: WILEY

摘要:

The dc current collected by a rocket‐borne cylindrical probe with various bias potentials has been measured, along with the plasma parameters (by in situ independent measurements on the same payload). Periodic variations synchronous with the rocket spin cycle appear; they are related to wake effects for the ion current and to both wake andV × Beffects for the electron current. The ion current modulations are quantitatively explained by a theory on the wake which takes account of the angle between the velocity and the rocket axis; the electron current modulations due to theV × Bfield are separated from the others and quantitatively explained by simple calculations. As a by‐product the ion current outside the wake gives an unperturbed density measurement in agreement to within 15% with an independent measur

ISSN:0148-0227    

DOI:10.1029/JA081i004p00450

年代:1976

数据来源: WILEY

摘要:

Large intensities of low‐energy protons were observed deep within the Jovian magnetosphere with the plasma instrumentation on Pioneer 10 during the encounter of this space probe with Jupiter. The energy range of the electrostatic analyzer was 108 eV to 4.80 keV during encounter. Inside the flux tubes of the Galilean moon Io is a ‘plasmasphere’ of protons with relatively high densities, 50–100 cm−3, extending toward the planet to at least 2.8RJ. The characteristic thermal energies of these protons are about 100 eV. The flux tubes of Io are positioned on a severe decrease of these densities with increasing Jovicentric radial distances—a plasmapause. The relationship of Io to this plasmapause is quite likely to be fundamental to the Io modulation of decametric radio emissions. The proton densities in the vicinity of Io are also sufficiently high to limit the azimuthal extent of the partial torus of hydrogen gas from Io by the mechanism of charge exchange. At greater distances, beyond the plasmapause, is found a great torus of plasma encircling Jupiter with densities in the range 10–15 cm−3and thermal energies about 400 eV. The moon Europa is embedded in this torus, or ‘ring current.’ This ring current is extended into a thin plasma disc at greater radial distances. At 15RJthe thickness of this disc is only 2RJ, and proton densities are about 1 cm−3. The source of these low‐energy protons is believed to be the Jovian ionosphere. The mechanisms for the formation of the Jovian plasmasphere, ring current, and plasma disc must differ substantially from those dominantly participating in the te

ISSN:0148-0227    

DOI:10.1029/JA081i004p00457

年代:1976

数据来源: WILEY

摘要:

Enhancements in power spectra of solar wind ion flux in the frequency neighborhood of 0.5 Hz had been noted by Unti et al. (1973). It was speculated that these were due to convected small‐scale density irregularities. In this paper we examine 54 flux spectra, calculated from Ogo 5 data. It is seen that the few prominent spectral peaks which occur were not generated by density irregularities but were due to several different causes, including convected discontinuities and propagating transverse waves. A superposition of many spectra, however, reveals a moderate enhancement at a frequency corresponding to convected features with a correlation length of a proton gyroradius, consistent with the results of Neugebauer (1975

ISSN:0148-0227    

DOI:10.1029/JA081i004p00469

年代:1976

数据来源: WILEY

摘要:

Far ultraviolet imagery of the earth in the 1050‐ to 1600‐Åand 1250‐ to 1600‐Å wavelength ranges was obtained from the lunar surface during the Apollo 16 mission on April 21, 1972. The images have an angular resolution of about 2 arc min (230‐km linear resolution) and have been quantitatively analyzed to obtain absolute intensities and spatial distributions of the polar auroras (both wavelength ranges) and of the day and night airglow and tropical airglow belts (1250‐ to 1600‐Å wavelength range). The observations are consistent with previous results obtained from the Ogo 4 spacecraft, but in addition, they have provided new details on the spatial distributions of the various emissions over an entire hemisphere at a single time. A general night airglow, at least in the northern hemisphe

ISSN:0148-0227    

DOI:10.1029/JA081i004p00483

年代:1976

数据来源: WILEY

摘要:

New measurements by ground‐based spectroscopy of the N2Vegard‐Kaplan system have given values for the υ′ progression intensities from υ′ = 0 to υ′ = 3 and upper limits to the values from υ′ = 4 to υ′ = 6. These are combined with other recent measurements of the N21P system and theoretical estimates of direct electron impact excitation to theA³Σ state to yield estimates of the rate coefficient for quenching of theA³Σ state by O and the variation of this coefficient with υ′. For the υ′ = 0 level a rate coefficient of 7.5 ± 5.0 × 10−11cm³ s−1is found to be consistent with reasonable assumptions as to atmospheric composition and auroral luminosity profile. It is concluded that this coefficient must

ISSN:0148-0227    

DOI:10.1029/JA081i004p00497

年代:1976

数据来源: WILEY

摘要:

Data from the VLF receivers aboard the Alouette and Isis spacecraft contain a number of examples of the ‘saucer’ radio phenomenon, so named because of its hyperbolic shape in the amplitude‐frequency‐time displays. These have been interpreted in terms of a model involving a small source of emission. Frequency‐time signatures have been calculated by using a ray‐tracing program assuming that the appropriate dispersion curves are those of the whistler mode on its resonance cone surface. Spatial dimensions of the sources have been deduced: typically, these are 0.5 km horizontally by no more than 10 km vertically. Total power radiated is about 10 mW. In the model, suprathermal electron beams flow through the source region and engage in an instability with background electrons. The deduced source dimensions are consistent with quantitative predictions of beam‐

ISSN:0148-0227    

DOI:10.1029/JA081i004p00501

年代:1976

数据来源: WILEY

摘要:

Thermal plasma density measurements obtained by using the spherical electrostatic analyzer probe carried by the polar orbiting satellite Isis 1 have been spectrally analyzed to provide quantitative results on the amplitude and scale size distribution of the plasma irregularities in the high‐latitude top side ionosphere. The range of scale sizes examined, 200 m to over 100 km under normal conditions, is more than an order of magnitude greater than that available from ground‐based measurements. Data in the altitude range 574–3523 km and from the period February 1969 to April 1972 have been analyzed. Irregularities in the high‐latitude region from 40° invariant latitude up to the invariantLpole have been studied. In over 90% of the cases examined, the power spectra are found to fit a power law of the formP=P0f−β, where the index β varies within the range 1.5–2.5. The power spectral density was integrated over the scale size range 1–10 km in order to analyze quantitatively latitudinal variations of the irregularity amplitude. While the boundaries of the high‐latitude irregularity zone on particular orbits examined by using this technique are in agreement with earlier morphological studies, it is also evident that the amplitude of the irregularities within the high‐latitude irregularity region itself shows irregular enhancements above a generally ra

ISSN:0148-0227    

DOI:10.1029/JA081i004p00515

年代:1976

数据来源: WILEY