摘要:

A detailed examination is made of the intensity variations of 3‐ to 12‐Mev interplanetary electrons. The data are from the Goddard cosmic‐ray experiment on the Imp satellites and cover the period from just before the last solar minimum through the onset of the present solar maximum (i.e., from December 1963 through August 1969). A morphology for the intensity changes is tentatively proposed that includes solar‐flare‐associated events, solar corotating increases, Forbush decreases, quiet‐time increases, and the long‐term 11‐year variation. It is contended that the electron components observed both during quiescent times and during quiet‐time increases are galactic in origin. The quiet‐time increases represent a completely new phenomenon that appears to be unique to the low‐energy electron population. During a quiet‐time increase the electron intensity is enhanced by a factor of 3–5 over a period of days, and, in general, these periods anticorrelate with low‐energy solar particle events. Qualitatively, their amplitude diminishes with increasing solar activity. One possible explanation for the origin of quiet‐time increases, which involves the augmented penetration of galactic electrons into the inner solar system, is suggested in the accompanying paper by Fisk and VanHollebeke (1972). Because of the large short‐term changes, the 11‐year modulation of these low‐energy galactic electrons is not well defined. An upper limit of a factor of 2.3 is placed on the intensity change observed

ISSN:0148-0227    

DOI:10.1029/JA077i013p02213

年代:1972

数据来源: WILEY

摘要:

One possible explanation for the increases in the intensity range of 3‐ to 12‐Mev interplanetary electrons that McDonald et al. (1972) have labeled as ‘quiet‐time electron increases’ is discussed. It is argued that the electrons in quiet‐time increases are galactic in origin but that the observed increases are not the result of any variation in the modulation of these particles in the inner solar system. It is suggested instead that quiet‐time increases may occur when more electrons than normal penetrate a modulating region that lies far beyond the orbit of the earth. The number of electrons penetrating this region may increase when field lines that have experienced an unusually large random walk in the photosphere are carried by the solar wind out to the region. As evidence of this increased random walk, it is shown that five solar rotations before most of the quiet‐time increases occur there is an extended period when the amplitude of the diurnal anisotropy (measured by the Deep River neutron monitor) is relatively low. A delay time of five rotations implies that the proposed modulating region lies at ∼30 AU from the sun if the average solar‐wind speed is assumed to be constant at ∼400 km/sec over this distance. The implications for the correlation between periods of low‐amplitude diurnal anisotropy and quiet‐time increases on interplanetary conditions out to ∼30 AU and some possible models for the proposed modulating

ISSN:0148-0227    

DOI:10.1029/JA077i013p02232

年代:1972

数据来源: WILEY

摘要:

A pair of sharp closely spaced discontinuities in the solar wind was recorded by the high time resolution instruments aboard Ogo 5 on March 14, 1968. There is plasma turbulence within the double structure, and there appear to be small‐amplitude hydromagnetic waves radiating from the discontinuities. The generation of the plasma turbulence is discussed in terms of magnetic drift waves. Although it seems probable that the surfaces are tangential discontinuities, arguments are also advanced that the double structure may represent the Petschek mechanism in which rapid field‐line merging occurs between standing wa

ISSN:0148-0227    

DOI:10.1029/JA077i013p02250

年代:1972

数据来源: WILEY

摘要:

The perturbation vectors of waves upstream and downstream from the region of maximum compression in the bow shock were examined on Ogo 5 under particularly steady solar‐wind conditions. The polarization of the upstream waves was right‐hand circular, and that of the downstream waves left‐hand elliptical in the spacecraft frame. By observing that the polarization of the waves remained unchanged as the shock motion swept the wave structure back and forth across the satellite 3 times in 8 min, it was found that the waves were not stationary in the shock frame. A study of the methods of determining the shock normal indicates that the normal estimated from a shock model should be superior to the normal based on magnetic coplanarity. The propagation vectors of the waves examined did not coincide with the shock‐model normal, the average magnetic field, or the plasma‐flow velocity. However, the major axis of the polarization ellipse of the downstream wave was nearly parallel to the upstream propagati

ISSN:0148-0227    

DOI:10.1029/JA077i013p02264

年代:1972

数据来源: WILEY

摘要:

We present a general survey of the Ogo 5 plasma‐wave measurements for the dayside polar‐cusp encounters of November 1, 1968, and a detailed analysis of the observations at the low‐altitude (r≃ 3–5RE) cusp boundaries. The survey section contains an over‐all discussion of the ULF magnetic‐field wave levels and the VLF electric‐field amplitude ranges measured from perigee out to 9REon November 1, 1968. These cusp‐associated observations are compared with those made on October 27 and November 6, 1968, when Ogo 5 traversed the dayside magnetosphere without encountering the cusp. At the November 1 low‐altitude cusp boundaries, we show that intense wave levels were detected over a broad spectral region at the steep gradients in cusp plasma density and thermal energy. The results are interpreted in terms of drift instabilities for low‐β plasmas with hot ions, and associated wave‐particle and wave‐wave interact

ISSN:0148-0227    

DOI:10.1029/JA077i013p02274

年代:1972

数据来源: WILEY

摘要:

Magnetosheath electrons precipitating into the dayside auroral oval are a significant source of ionization and consequently will lead to electrical conductivity enhancements within the oval. By assuming that the electrons are maintained isotropic by strong pitch‐angle diffusion as they precipitate into the ionosphere, the precipitation heat flux can be simply related to solar‐wind energy density and consequently to the level of magnetic activity. For quiet solar‐wind conditions, the heat fluxes of 1–10 ergs cm−2sec−1expected and observed lead to height‐integrated Pedersen conductivity enhancements of 4–15 mhos. During magnetic storms the conductivity enhancements could increase by a factor of 3 to 5. Since the precipitating electrons are soft, the Hall conductivity enhancements are smaller than the Pedersen conductivity enhancements. For typical electric fields the computed conductivity enhancements lead to field‐aligned currents bounding the enhancements in order‐of‐magnitude agreement with observation. The topside ionosphere should also have a density enhancement over the aurora

ISSN:0148-0227    

DOI:10.1029/JA077i013p02294

年代:1972

数据来源: WILEY

摘要:

It is shown that there is a close relationship between the range of the equatorward shift of the midday aurora and the magnitude of a negative bay at an auroral‐zone station in the midnight sector. Their time variations are also similar. This relationship can be taken to be a clear indication of a close association of magnetospheric substorms with the transfer of the magnetic flux from the front of the magnetosphere to the magnetotail. Furthermore, the intensity of magnetospheric substorms appears to be approximately proportional to the net amount of transferred magnetic flu

ISSN:0148-0227    

DOI:10.1029/JA077i013p02303

年代:1972

数据来源: WILEY

摘要:

The proton energy spectrum in the inner Van Allen zone was investigated in the range 30 to 300 Mev with a solid statedE/dxtelescope aboard the Esro 2 satellite. TheB‐Ldomain covered is 1.3 ≤L≤ 2.4 and 0.18 ≤B≤ 0.24. It was found that an exponential spectrumf[E] =N0exp (—E/E0) is a good fit to the data in the rangeL= 2 toL= 2.4. ForLEc,f[E] =N0exp (—E/E0). From our data, the variations withLof the parametersEc,E0,E1were found to be (a)E1= (148 ± 8) Mev; (b)E0= (290 ± 20)L−3.3±0.3; and (c)Ec= (400 ± 20)L−3±0.2. We suggest that two injection mechanisms are operating for all of this energy range, and that they give rise to two populations. The first one is the main component at energies lower than 25 Mev. At energies higher than our threshold (30 Mev), the detected fluxes are the addition of a second population (main component) and the high‐energy tail of the first population. The spectrum of this second population appears to have the characteristic shape of a spectrum altered by ionization losses and generated by a continuous source, the slope fo

ISSN:0148-0227    

DOI:10.1029/JA077i013p02309

年代:1972

数据来源: WILEY

摘要:

The payload of polar‐orbiting Ogo 6 included a narrow‐band (≃200 Hz) receiver at 200 kHz connected to an electric dipole antenna. We have studied the signals recorded by this receiver at the station and in the conjugate region of Achkhabad (58°23′E, 37°57′N). The latitude of this station is nearly low enough (≃30.5° invariant latitude) for propagation of a 200‐kHz signal in the ducted whistler mode to the conjugate hemisphere along field lines terminating at the station. In the dawn‐dusk orbital plane signals are indeed relatively often observed in the conjugate region, but the source of the signals and their path of propagation is not completely clear. The pattern of observations is consistent with propagation over the long magnetospheric path in field‐aligned ducts spread in longitude near 22° invariant latitude, but we favor an interpretation involving nonducted propagation in which the occasionally high electric‐field intensities encountered (>10 μv/m) result from focusing effects or from propagation

ISSN:0148-0227    

DOI:10.1029/JA077i013p02319

年代:1972

数据来源: WILEY

摘要:

Using the qualitative ideas of convection electric fields over the earth's polar regions, we demonstrate the importance of ion drag in establishing a thermospheric wind system. Recent measurements indicate that uniform electric fields of 10 to 40 mv/m are a regular feature of the polar‐cap ionosphere. Calculations of the neutral thermospheric wind, using these measured fields in a simple ionospheric model, have been made. The time scale for motion of the neutral gas ranges from less than 1 hour atF‐region heights to about 2 hours in the dynamo region of the ionosphere. It has been found that the viscosity of the atmosphere is important in determining the winds in the dynamo region. Results are given that show ion‐temperature enhancements of hundreds of degrees that are due to ion‐neutral frictional effects. In addition, the total deposition rate of convection energy in the polar thermosphere is shown to be of the same order of magnitude as that due to absorption of solar EUV radiation. The implications of these results for the dynamics and energetics of the thermosphere are di

ISSN:0148-0227    

DOI:10.1029/JA077i013p02328

年代:1972

数据来源: WILEY