摘要:

A preliminary analysis of some of the Skylab extreme ultraviolet (EUV) occultation data is presented. Radiation at the wavelengths of three strong solar emission lines near 1335, 1216, and 1032 Å is absorbed by O2in the terrestrial atmosphere at altitudes between 90 and 160 km. It was found that the laboratory values for the absorption cross sections at these three wavelengths and the appropriate Jacchia model for the average atmospheric O2densities needed only small adjustments to be consistent with the mean altitudes of unit optical depth determined from a number of the Skylab occultation profiles. However, the altitudes of unit optical depth,h0, tended to increase with latitude (and magnetic activity) at 1355 and 1032 Å, although only a small latitudinal effect was observed at 1216 Å. The values ofh0were also about 2 km lower at sunrise than at sunset at 1216 Å, possibly a small diurnal effect remaining at 1335 and 1032 Å. For future EUV occultation studies it is recommended that an instrument field of view of about 1 × 1 (arc min)² be employed both to provide good altitude resolution and to minimize spatially coherent intensity fluctuations from small features on the sola

ISSN:0148-0227    

DOI:10.1029/JA082i032p04973

年代:1977

数据来源: WILEY

摘要:

Fluctuations of theFregion electron density in the gravity wave period range have been monitored by using the Arecibo incoherent scatter radar. The radar was pointed in the vertical direction, and a transmitted pulse 50 µs in length was used to provide 1‐min time resolution time series of 4‐ to 30‐hour duration at several altitudes in the altitude range of 197.85–485.85 km. Spectral analysis has been performed on 4‐hour segments of these time series. Spectral peaks recurring at a nearly constant frequency over the entire altitude range of this experiment were taken to be the ionospheric response due to the passage of an internal gravity wave. Relative phase information at the corresponding frequency can be obtained from the time series data. This response in magnitude and phase was fit to an atmospheric model to yield the parameters of causative internal gravity waves. Two cases are presented and compared to a dispersion relation, generally good agreement being obtained. Discrepancies in the agreement for the imaginary part of the wave number can be attributed to inaccuracies in the model atmosphere, but a disagreement found between the experimental results for the real part of the wave number and the dispersion relation at altitudes above the electron density maximum is of unkn

ISSN:0148-0227    

DOI:10.1029/JA082i032p04983

年代:1977

数据来源: WILEY

摘要:

The data of an early report tentatively linking the radial orientation of the interplanetary magnetic field (IMF), measured by Explorer 35, with ULF activity in the Pc 3–4 range observed at Calgary in September 1969 have been supplemented by data from October and November 1969. The larger sample of hourly values confirms the results discerned before: (1) there is a contribution to Pc 3 and 4 signal amplitudes that disregards the conventional separation between the bands at T = 45 s; (2) the contribution is apparent under quiet conditions when Kp ≤ 2o; (3) the contribution comes from signals whose probable amplitude is highest when the field is along the sun‐earth line and lowest, essentially at instrument threshold, when the angle θXBbetween X(GSE) and B (the IMF) exceeds about 60°; (4) the trend of high signal amplitude with low θXBis replaced by cos θXB, suggesting a propagation property of waves in the solar wind; and (5) the trend and its properties are compatible with, although not compelled by, a model of signal origin in quasi‐parallel bow shoc

ISSN:0148-0227    

DOI:10.1029/JA082i032p04991

年代:1977

数据来源: WILEY

摘要:

Rocket observations of the extreme ultraviolet spectrum of the aurora from 550 to 1250 Å are presented, and the results for the O I (989 Å) and O I (1027 Å) multiplets are examined in detail. The intensity of these emissions and the observed anisotropic radiation field are inconsistent with the relative intensity of the branching radiations. Several possible solutions to the problem are discussed, and evidence is presented that suggests the need to lower the branching ratios by several orders of magnitu

ISSN:0148-0227    

DOI:10.1029/JA082i032p04997

年代:1977

数据来源: WILEY

摘要:

High densities are sometimes observed in the solar wind when the bulk flow speed is nearly constant or falling. In contrast to the large density compressions observed on the rising speed portions of high‐speed streams, these high densities do not appear to be generated in interplanetary space. Typically, the magnetic field is not enhanced within these events, and the proton and/or electron temperatures are low and vary in opposition to the density. Approximately ⅓ of these density events contain interplanetary magnetic field reversals, although these reversals are often ‘noisy’ and usually do not qualify as sector boundaries. We estimate by assuming an areal extent that the average event contains approximately 1016g of material and 2.6 × 1031ergs so that the aggregated events, when they are common, make a nonnegligible contribution to the total mass and energy budget of the solar wind at 1 AU. Values of the frequency of occurrence, duration, mass, energy, and speed of these density enhancements are comparable to those of solar coronal mass ejection events, suggesting a direct but as yet unproved association between these p

ISSN:0148-0227    

DOI:10.1029/JA082i032p05005

年代:1977

数据来源: WILEY

摘要:

The far ultraviolet day airglow between 1130 and 1520 Å was observed at 4.4‐Å spectral resolution with a scanning spectrophotometer aboard an Aerobee rocket on December 11, 1972. Fourteen bands, or blends, of the N2Lyman‐Birge‐Hopfield (LBH) system are clearly resolved and indicate a total LBH system zenith column emission rate of 3810 ± 520 R extrapolated to the subsolar point. No LBH bands originating from vibrational levels with υ′>6 are observed, nor are any bands of the N2Birge‐Hopfield system observed. A photoelectron flux model, based on recent photoelectron flux measurements and the observed LBH altitude profile, is used to calculate the direct and dissociative excitation contributions to the atomic nitrogen emissions. An atomic nitrogen density of the order of 4 × 107cm−3at 190 km is required to account for the observed 77 ± 8 R N I λ 1493 intensity and the 580‐R N I λ 1200 intensity, both of which are produced primarily by direct electron impact excitation of atomic nitrogen. This density is in agreement with other recent measurements but is an order of magnitude greater than earlier photoc

ISSN:0148-0227    

DOI:10.1029/JA082i032p05011

年代:1977

数据来源: WILEY

摘要:

An investigation is made of the short‐term persistence of certain features of electron precipitation in the slot region: the total precipitating flux levels and the occurrence of peaks having stronglyL‐dependent central energies. The latter phenomenon is of special interest, since the peaks have been shown to be consistent with the idea that the responsible mechanism is wave‐particle interactions with a narrow frequency band of waves. At a given magnetic local time the equivalent wave frequencies which may be responsible for the peaks are found to have statistically significant correlation coefficients between pairs of passes separated by 100 min or less. The total electron intensities of>130 keV have significant correlation coefficients for separation times of 24 hours or less. These findings are consistent with a significant electron precipitation resulting from a slowly varying hiss band, in preference to a more random occurrence of discrete emis

ISSN:0148-0227    

DOI:10.1029/JA082i032p05024

年代:1977

数据来源: WILEY

摘要:

A comprehensive study of growth phase and substorm activity following a period of magnetic calm has been conducted through a network of all‐sky camera stations, auroral zone magnetic observatories, and particle detectors aboard the Isis 1 satellite. We have carefully documented the observations with the following results. The preexpansive phase arc which extended at least from 17 to 05 MLT was responsible for an energy input rate of ≃3 × 1016ergs/s before breakup. An equatorward drift of this arc of 6 km/min, observed only in the evening sector, remained until after the expansive phase, when its motion stopped abruptly at the time of the maximum poleward displacement of the arcs. Electrons responsible for the prebreakup arc had energies of ≃1–5 keV. Protons of ≃4‐keV energy were measured equatorward of the electron arc. During the expansive phase, symmetrically traveling disturbances were observed propagating eastward in the evening sector and westward in the morning sector. The propagation stopped for 1–2 min at the time of maximum expansion and then continued, thus suggesting a momentary variation in the rate of convection. Equivalent currents consistent with observed magnetic perturbations represented approximately the sameDPZ(twin vortex) pattern before the expansive phase as during it; however, although the magnitude of the currents was greater during the expansive phase, the dominant feature during this phase was an intense westward auroral electrojet. The camera observations of diffuse cloudlike aurora showed an injection of ≃40‐keV electrons during the expansive phase along the auroral oval between midnight and 0400 corrected geomagnetic time. Movement of the cloud indicated an eastward gradient drift of the e

ISSN:0148-0227    

DOI:10.1029/JA082i032p05031

年代:1977

数据来源: WILEY

摘要:

The incoherent scatter radar at Chatanika, Alaska, has been used to study electric fields and horizontal currents associated with auroral arcs. Examples are given of arcs observed at three local times: in the evening, at the time of the midnight reversal of the north‐south electric field, and in the early morning. Within the arcs the observed electric field is decreased in the early evening case and increased in the morning case. In all three examples there is a southward polarization field within the arc. The direction of this field is determined by the direction of the east‐west field, which, in all three cases, is westward within the arc. The northward field variations are an ionospheric response to the increased conductivities, whereas the data indicate that the westward field variations originate above the region of enhanced conductivities. In one case it is found that the westward field behavior is correlated with the low‐energy electron precipitation. The electric field variations influence the amplitude and the direction of the electrojet current. Outside the arc the current flows parallel to the arc alignment; inside the arc the current flows almost perpendicular to the arc alignment. In addition, upward‐flowing field‐aligned currents are found to exist withi

ISSN:0148-0227    

DOI:10.1029/JA082i032p05051

年代:1977

数据来源: WILEY

摘要:

Equatorial cold plasma density profiles determined from VLF whistlers propagating in magnetospheric ducts are compared with densities computed from the observations of ULF hydromagnetic waves (geomagnetic pulsations). The densities obtained by the ULF technique are based on the identification of resonant geomagnetic field lines, assumed to be driven by a monochromatic source. The ULF results thus obtained agree well with the whistler results throughout the period, June 17–20, 1973, when simultaneous data comparisons could be made. The ULF observations show that at mid‐latitudes, shorter‐period resonances can be supported in the plasma trough region, while those of longer period can occur inside the plasmas

ISSN:0148-0227    

DOI:10.1029/JA082i032p05063

年代:1977

数据来源: WILEY