摘要:

A study has been made of 16 interplanetary shock waves observed in 1968 by Pioneer 8 at large distances from earth. A comparison with the shapes of interplanetary shock fronts obtained by De Young and Hundhausen (1971) suggests that in general the ejection of flare gas occurs within a cone of half‐angle between 30° and 60°. For near‐earth events a deflection of the shock front has been observed, possibly owing to an interaction with the bow shock. The average duration of the post shock perturbation is about 20 hours. Strong magnetic fields and rapid fluctuations occur during the first 6–12 hours. Electric field perturbations in the VLF band are also noted during these periods. There is limited evidence for one corotating shock in these data. Unfortunately, no plasma data are available for the comparison and the interpretation of corresponding a

ISSN:0148-0227    

DOI:10.1029/JA078i022p04535

年代:1973

数据来源: WILEY

摘要:

Selected results are presented for an analysis of Mariner 9 1304‐A data from the first 100 passes. Based on a comparison of limb data, the exospheric temperature appears lower on several Mariner 9 passes than when Mariner 6 and 7 encountered the planet in 1969. Temperatures of 300° and 350°K are considered in the atmospheric modeling. At 300°, derived values of the atomic oxygen concentration are typically between 0.5% and 1% of the total density at 135 km, based on fitting theoretical intensities to limb data from several passes. Structure in the limb data below 200 km suggests the possibility that ∼0.2 kR of the observed ∼0.8 kR near 150 km is due to dissociative excitation of CO2. There is variability in limb profiles, thus indicating changes in the O distribution with time. The variability does not appear to follow a recognizable pattern. Interpretation of the 1304‐A disc data shows a correlation in intensity with the 10.7‐cm solar flux and larger O concentrations in the afternoon than in the morning. The correlation in intensity with the 10.7‐cm flux is probably due largely to variation in the solar 1304‐A fluxes. Selected disc data show localized and random enhancements

ISSN:0148-0227    

DOI:10.1029/JA078i022p04547

年代:1973

数据来源: WILEY

摘要:

Acceleration and detection of the lunar thermal ionosphere in the presence of the lunar electric field yields a value of at least +10 volts for the lunar electric potential for solar zenith angles between approximately 20° and 45° and in the magnetosheath or solar wind. An enhanced positive ion flux is observed with the Apollo Lunar Surface Experiments Package Suprathermal Ion Detector Experiment when a preacceleration voltage attains certain values. This enhancement is greater when the moon is in the solar wind as opposed to the magnetosheat

ISSN:0148-0227    

DOI:10.1029/JA078i022p04560

年代:1973

数据来源: WILEY

摘要:

The energy spectra and intensities of electrons>130 kev have been measured since October 1971 with two 256‐channel electron spectrometers on board the low‐altitude (∼800‐km) polar‐orbiting earth‐oriented satellite 1971 089A. In the inner radiation belt the energy spectra of the trapped electrons can often be characterized as exponential in shape, but during magnetic disturbances the trapped fluxes at the lower edge of the inner belt (L≲ 1.3) may be quite variable and may extend to lowerLvalues, and the energy spectra may display pronounced structure, such as the presence of one or more peaks. Several features of the data are in agreement with a set of observations made at a time when the Starfish electrons were dominant and are consistent with the origin of the peaks being a redistribution of the existing population. Peaks in the energy spectra are also frequently observed at the outer edge of the inner belt (L≈ 1.4–1.8), but several features of these peaks are in distinct contrast to those observed on very lowLshells. The energies of the peaks seen in the outer parts of the belt usually decrease very rapidly with increasingLvalue, whereas the energies of those seen at the lower edge of the belt are generally not strongly dependent uponL. AtL≈ 1.4 to 1.8 the most pronounced peaks occur more often at lowhminvalues; in contrast, structure in the spectra seen at the inner edge of the belt is usually more pronounced at higher values ofhmin. These and other differing characteristics suggest that the peaks in the outer portions of the belt are associated with precipitation processes and do not result from the same type of ‘redistribution inL’mechanism proposed for the nearly monoenergetic spectra sometimes seen at the lower edge of the inner belt. The observations suggest that peaks may originate from a cyclotron resonance interaction of electrons with whistlers of a nearly constant frequency ov

ISSN:0148-0227    

DOI:10.1029/JA078i022p04568

年代:1973

数据来源: WILEY

摘要:

Simultaneous measurements from the Isis 1 satellite of soft‐electron fluxes and of auroral hiss at low and medium frequencies indicate that such noise emissions can propagate to the north or south of theLshell containing the precipitating electrons through distances up to 1000 km or about 3° invariant latitude at 2000 km altitude. This latitudinal spreading suggests that the noise propagation corresponds to those parts of the whistler‐mode dispersion curves where the waves are electric, that is, near the resonance cone. The relative variations of the LF and MF spectra can be roughly accounted for by a simple ray‐tracing technique assuming electric waves. Ionograms recorded at the same time as the noise measurements were reduced to real height profiles of electron density, thus giving a two‐dimensional ambient electron distribution for ray tracing. Absolute intensities of noise have been computed by using observed electron flux densities and assuming an incoherent Cerenkov mechanism. The theoretical power levels are at least two orders of magnitude lower than those observed. It is concluded that the incoherent theory for the wave generation mechanism is inapplicable, assuming that the antenna impedance theory that was used is

ISSN:0148-0227    

DOI:10.1029/JA078i022p04578

年代:1973

数据来源: WILEY

摘要:

Measurements at conjugate points on the ground nearL= 4 of the power spectra of magnetic‐field fluctuations in the frequency range 0.5 to 20 mHz are used as a means of estimating daily values for the relativistic‐electron radial‐diffusion coefficientDLLfor two periods in December 1971 and January 1972. The values deduced forL−10DLLshow a strong variation with magnetic activity, as measured by the Fredricksburg magnetic indexKFR. The radial‐diffusion coefficient typically increases by a factor of ∼10 for a unit increase inKFR. WhenKFR≲ 2, it is generally found thatDLL≲ 2 × 10−9L10day−1for equatorially mirroring electrons having a first invariantM= 750 Mev/gauss; a value ofDLL∼4 × 10−7L10day−1is deduced for one day on which the meanKFRwas 4.5. The quantityL−10DLLtheoretically depends on energy andLas (L/M)(s−2)/2for relativistic particles, wheresis the logarithmic slope of the power‐law spectrum of magnetic fluctuations observed on the ground. For the time period analyzed,styp

ISSN:0148-0227    

DOI:10.1029/JA078i022p04600

年代:1973

数据来源: WILEY

摘要:

A numerical solution is obtained for the coupled differential equations governing the propagation of Pc 1 micropulsations in the ionospheric wave guide in directions out of the plane of the geomagnetic meridian. A significant difference from previously obtained in‐meridian results is the appearance of resonant absorption peaks at certain frequencies. The resonances arise from coupling between the ‘ducted’ mode and the ‘field‐guided’ mode, which removes energy from the wave guide. The resonant frequencies depend on ionospheric parameters and dip angle, but not on the direction of propagation. The amplitude of the resonances, however, increases with deviation from the geomagnetic meridian. The existence of geographically dependent frequency passbands implied by these results makes it questionable that micropulsations can propagate without appreciable attenuation in directions other than geomagnetic N‐S or possibly ge

ISSN:0148-0227    

DOI:10.1029/JA078i022p04611

年代:1973

数据来源: WILEY

摘要:

Wave propagation and refraction of ‘type I’ irregularities in the equatorial electrojet are investigated. Quantitative calculation of wave refraction in a model electrojet shows that the direction of wave refraction must change sign at one altitude. Waves propagating with the electrons rotate their wave vectors upward in the upper electrojet and downward in the lower electrojet during the day, and vice versa at night. Furthermore, the altitude region of largest linear growth rate is also the one with the weakest refraction rate. Consequently, computations of the ray‐path integrated wave growth show that this region would dominate the backscatter spectrum from the electrojet if linear theory were valid, and it is further noted that the maximum amplitude wave should have phase velocities exceeding the ion acoustic speed. We therefore conclude that propagation alone, without inclusion of nonlinear effects, cannot explain backscatter observations of a constant Doppler frequency shift given by the ion acoustic

ISSN:0148-0227    

DOI:10.1029/JA078i022p04619

年代:1973

数据来源: WILEY

摘要:

Ogo 4 observations of the O I (6300‐A) emissions have revealed a global pattern hitherto undetected from the ground‐based observations. It is seen that the postsunset emission of O I (6300 A) in October 1967 is very asymmetrical with respect to the geomagnetic equator in certain longitude regions and shows poor correlation with the electron density measured simultaneously from the same spacecraft. This asymmetry is less marked in the UV airglow, O I (1356 A), which appears to vary as the square of the maximum electron density in theFregion. The horizon scan data of the 6300‐A airglow reveal that the latitudinal asymmetry is associated with asymmetry in the height of the O I (6300‐A) emission and hence with the altitude of theF2peak. From the correlative studies of the airglow and the ionospheric measurements the mechanisms for the UV and the 6300‐A emissions are discussed in terms of the processes involving radiative and dissociative recombination. Theoretical expressions are developed relating the airglow data to the ionospheric parameters, and it is shown that the agreement between observed and calculated emission rates is well within the uncertainty of the mea

ISSN:0148-0227    

DOI:10.1029/JA078i022p04630

年代:1973

数据来源: WILEY

摘要:

Ultraviolet emissions above 540 km have been detected in the equatorial zone at a local time near 1800 with instruments aboard the TD1 A astronomical satellite. The main features of the emissions can be accounted for by resonance scattering of sunlight by Mg+ions. The observations confirm previous mass spectrometric measurements of metallic ions in the equatorial ionosphere and generally are consistent with the vertical transport mechanism proposed by Hanson and others. The emissions often are highly asymmetrical with respect to the magnetic dip equator, possibly indicating the effect of transequatorial neutral winds. Additional weaker equatorial emissions have been tentatively identified with Fe+, O+, and possibly Si+ions geographically distinct from the Mg+ions.

ISSN:0148-0227    

DOI:10.1029/JA078i022p04641

年代:1973

数据来源: WILEY