摘要:

Analysis of Imp 1 (Explorer 43) interplanetary plasma and magnetic field fluctuations on a scale of 1 hour for the period March 18 to April 7, 1971, reveals that linearly and circularly polarized Alfvén waves were rarely present. Fluctuations having most of the characteristics of large amplitude‘Alfvén waves’ were observed ≈40% of the time and moved away from the sun nearly alongB. These were not pure transverse Alfvén waves, however, because they were accompanied by nonzero fluctuations in the magnetic field intensity. No simple relation between ‘Alfvén waves’ and stre

ISSN:0148-0227    

DOI:10.1029/JA081i001p00073

年代:1976

数据来源: WILEY

摘要:

Analysis of data obtained by Ogo 5 confirms the Imp 6 observations of the inverse dependence of the helium to hydrogen temperature ratioTHe/THon τe/τc, the ratio of the solar wind expansion time to the Coulomb collision equipartition time. The difference between the absolute values of the averages ofTHe/THas observed by Imp and Ogo is probably due to the difference of the weights given to high‐ and low‐velocity periods by the two experiments. The magnitude of the differential flow vector Δυ = |vHe‐ vH| varies inversely with τe/τs(where τsis the Coulomb collision slowing‐down time) when τe/τsis small and approaches zero when τe/τsis large. The data suggest a model of continuous preferential acceleration and heating of helium (or deceleration and cooling of hydrogen) which is opposed and limited by Coulomb collisions. Since the average dependence of Δυ on τe/τscannot explain all of the systematic variations of Δυ observed in corotating high‐velocity streams, extra helium acceleration (or hydrogen deceleration) probably occurs on the le

ISSN:0148-0227    

DOI:10.1029/JA081i001p00078

年代:1976

数据来源: WILEY

摘要:

Observations made by the ultraviolet spectrometer on board the orbiting geophysical observatory Ogo 4 confirmed the presence of resonance scattering at 2800 Å of Mg+ions in the twilight subtropical ionosphere. The column density reached 4 × 109ions cm−2above 160 km. Photometric measurements by the Esro TD 1 satellite revealed a maximum of the Mg+abundance at equinoxes in the top sideFregion. The interhemisphere asymmetries observed in the intensity distribution are essentially attributed to the effect of eastward thermospheric winds. The 2800‐Å doublet was also detected by Ogo 4 at middle and high latitudes from 110 to 250 km. The brightness of the emission and other evidence indicate that evaporation of meteoritic matter cannot explain the abundance of ions at 200 km. Therefore Mg+ions are probably transported upward from the 100‐km permanent sour

ISSN:0148-0227    

DOI:10.1029/JA081i001p00083

年代:1976

数据来源: WILEY

摘要:

In this paper we address the question of whether auroral echoes are dependent on the ionospheric electric field. This question naturally arises from the concept of a plasma instability as the source mechanism producing the electron density irregularities responsible for the auroral echoes. Using the data from a backscatter radar located at Homer, Alaska, and the Chatanika incoherent scatter radar in a joint experiment, we show that there is a distinct dependence of the occurrence of diffuse auroral echoes on a threshold electric field strength. The threshold value for the 398‐MHz radar aurora is shown to be approximately 30 mV/m. When the electric field strength is greater than 30 mV/m, the auroral echo strength is shown to be always positively correlated with the electric field strength, regardless of the mean electron density. On the other hand, the auroral echo strength is not always positively correlated with the electron density. The results are shown to be consistent with the quasi‐linear plasma instability theory of Sudan et al. (1973) and Greenwald (19

ISSN:0148-0227    

DOI:10.1029/JA081i001p00088

年代:1976

数据来源: WILEY

摘要:

All‐sky camera (ASCA) observations were made at the field line conjugate of the ATS 5 satellite. The field of view of these cameras covered the region of the magnetosphere fromL= 5 toL= 11 at the approximate longitude of the ATS field line conjugate. With this coverage, definite statements can be made concerning the correlation of the auroras observed by the ASCA's and the magnetospheric trapped fluxes. In general, auroral forms are not simply correlated with the synchronous altitude electron fluxes. The presence of hot plasma at the ATS 5 satellite is a necessary but not sufficient condition for the occurrence of local auroras. On quiet days the hot plasma does not penetrate into the magnetosphere far enough to reach the ATS 5 orbit. Under these conditions, no auroras are observed at the field line conjugate, but auroras are usually observed on higher‐latitude field lines. On more disturbed days, auroral arcs are observed at lower latitudes when the plasma sheet penetrates into the ATS 5 orbit. There is no general correlation between the intensity of the trapped electron fluxes observed by ATS 5 and the intensity of auroras observed by the ASCA's. Auroral displays exhibit very fast fluctuations, whereas the ATS 5 electron fluxes change on a much slower time scale. However, significant qualitative correlation between the ASCA data and the trapped fluxes is observed when a local plasma injection event occurs near ATS 5. The clearest signature of the injection event is magnetic and is most pronounced as a recovery of a negative bay in the north‐south component of the field at the ATS 5. The local injection generally produces structured auroras such as breakup events and sometimes westward‐traveling surges. A significant correlation is observed with the intensification of a diffuse uniform glow accompanying the structured auroral a

ISSN:0148-0227    

DOI:10.1029/JA081i001p00097

年代:1976

数据来源: WILEY

摘要:

Aluminum and platinum foils were flown into two bright auroras and subsequently recovered. They were then analyzed for traces of trapped noble gases in a sensitive high‐resolution mass spectrometer. In this paper we report the detection of ³He and confirm measurements of the4He flux reported in a previous paper. The4He∶³He ratio in the first (brighter) aurora was 2950 ± 250. This ratio is only slightly higher than the average solar wind ratio of 2350 and since the atmospheric ratio is grossly different (250 times larger), establishes the solar wind as the principal source of auroral helium, at least in the aurora concerned. The result supports earlier suggestions that auroral precipitation is one of the main sources of the ³He in the terrestrial atmosphere. Current estimates of ³He sources and loss rates are found to be consistent with a balanced atmospheric ³

ISSN:0148-0227    

DOI:10.1029/JA081i001p00111

年代:1976

数据来源: WILEY

摘要:

A rocket‐borne experiment to study the currents associated with a system of multiple auroral arcs was conducted at Poker Flat, Alaska, at 1122 UT on February 2, 1972. The magnetic field in the vicinity of the auroral system was measured with a cesium vector magnetometer. Possible configurations were inferred by constructing model current systems that reproduced the magnetic field variations measured along the flight path. The data are interpreted in terms of a model current system consisting of two eastward electrojets and one westward electrojet and three pairs of oppositely directed Birkeland sheet currents, all lying in a plane approximately parallel to the auroral arcs. Sheet thicknesses ranged from 20 to 60 km and current densities from 10 to 45 µA/m²; the electrojet currents ranged from 1000 to 2000 A. A possible alternate model consisted of four pairs of sheets whose thicknesses range from 10 to 40 km with current densities from 10 to 90 µA/m². There was quite good agreement between the locations of the visual arcs and the upward current sheets. The overall current configuration is discussed in view of the theoretical models constructed by Atkinson and Sato and Holzer and of other observa

ISSN:0148-0227    

DOI:10.1029/JA081i001p00116

年代:1976

数据来源: WILEY

摘要:

Differential energy spectra of electrons observed in an auroral breakup show evidence that an incident electron beam of energyE= 6–13 keV, width of 2–5 keV, and variable intensity was stabilized over a period of at least several minutes by the oscillating two‐stream instability in the manner previously described by Papadopoulos and Coffey. The critical observed feature predicted by these authors' calculation is a tail with differential fluxdj/dE∝E−0.5. This tail is much too intense to be attributed to the effects of collisions with atmospheric constituents. It is possible that the tail is part of the beam itself, i.e., produced higher up, but there are at least two arguments against this: first, the observations indicate that the tail approaches isotropy, whereas the beam is mostly downcoming, and second, the tail is observed as low as 130 km; the portion of the tail below 1.5 keV would have been absorbed by the atmosphere at greater heights if it had been incident from above. The observations support the hypothesis that the tail electrons are produced locally and by the proposed stabilization process. Implications are briefly

ISSN:0148-0227    

DOI:10.1029/JA081i001p00123

年代:1976

数据来源: WILEY

摘要:

Observations with an altitude resolution of about 1 km were made with the large, vertically directed 50‐MHz radar system at the Jicamarca Radar Observatory during the day, when the electrojet was strong. Type 1 (‘two stream’) echoes were seen in a limited range of altitudes, with Doppler shifts corresponding to upward and downward motion at the acoustic velocity. Most of the radar returns were due to type 2 echoes, however. The direction of motion of the type 1 waves sometimes reversed in as little as 1 s, supporting a turbulent model of the electrojet region. During the day the upgoing type 1 waves were observed to be somewhat more easily excited than the downgoing waves, an effect similar to an east‐west asymmetry noted in earlier studies. The correspondence between the Jicamarca radar observations and rocket measurements in India is di

ISSN:0148-0227    

DOI:10.1029/JA081i001p00130

年代:1976

数据来源: WILEY

摘要:

Auroral electron precipitation in the morning sector is assumed to be the result of an electromagnetic cyclotron instability of a particle distribution that evolves adiabatically as its constituent electrons drift eastward from a source near midnight. The adiabatic distribution is calculated by using Green's function in various magnetospheric field models, and the corresponding growth rates for whistler mode waves are calculated by the method of Kennel and Petschek (1966). The region of maximum calculated wave growth corresponds spatially and temporally to the region of maximum observed electron precipitation only when the magnetospheric electric field is included realistically in the model.

ISSN:0148-0227    

DOI:10.1029/JA081i001p00135

年代:1976

数据来源: WILEY