摘要:

A mean value for the 1 AU total solar irradiance of 1368.2 W/m2and a downward trend of 0.05% per year were derived from measurements by the Active Cavity Radiometer Irradiance Monitor (ACRIM) experiment on the Solar Maximum Mission during 1980. Distinct temporary solar irradiance decreases associated with solar activity maxima were observed with a series of nine dips from April to October recurring at fairly regular intervals averaging 24 days. The decreases correlate inversely with sunspot area, 2800‐MHz flux, and Zurich sunspot number. Dominant periods common to the irradiance and sunspot area power spectra link the irradiance decreases to sunspot flux deficit in solar active regions. Evidence of significant total irradiance modulation by facular flux excess is cited. A persistent radiative cycle of active regions consistent with the ACRIM irradiance results and the morphology of solar active regions was found. The pattern of regularly recurrent active region maxima between April and October suggests an asymmetry in solar activity generation during this perio

ISSN:0148-0227    

DOI:10.1029/JA087iA06p04319

年代:1982

数据来源: WILEY

摘要:

Data from the Johns Hopkins University Applied Physics Laboratory charged particle measurement experiment aboard IMP 8 was used to study solar flare events and find correlations between soft X rays (4–17 Å) and particle events. The results show that a greater probability exists of observing a proton event if the observed soft X ray flare has a relatively large decay time. It is also found that the Hα brightening area is a good indicator of the strength of the soft X ray burst. Results also show that the strength of the soft X ray burst can be used to estimate a probability that a proton event will occur, along with the strength of that particle ev

ISSN:0148-0227    

DOI:10.1029/JA087iA06p04327

年代:1982

数据来源: WILEY

摘要:

A Monte Carlo simulation of the propagation of relativistic solar flare protons in the interplanetary magnetic field was used to understand the intensity‐time profiles and anisotropies for the GLEs on November 22, 1977 and May 7, 1978. Mean free paths for pitch angle scattering of 0.5 AU and 5 AU, respectively, were deduced. The injection of the solar flare protons had an extended time structure that was found to be of similar shape as the x ray burst profiles in the bands 1–8 Å and 0.5–4 Å, respe

ISSN:0148-0227    

DOI:10.1029/JA087iA06p04338

年代:1982

数据来源: WILEY

摘要:

Observations by the Voyager 1 and 2 spacecraft of the interplanetary magnetic field between 1 and 5 AU have been used to investigate the large‐scale structure of the IMF in the years 1977 to 1979, a period of increasing solar activity. This complements the Pioneer 10, 11 investigation between 1 and 8.5 AU during 1972–1976 when the sun was less active. In contrast to the good agreement of the Pioneer observations with the ideal field configuration of the Parker spiral model during near solar minimum conditions, the Voyager spacecraft found notable deviations from that configuration. We attribute these deviations both to temporal variations associated with increasing solar activity, and to the effects of fluctuations of the field in the radial direction. The amplitude of the latter fluctuations was found to be large relative to the magnitude of the radial field component itself beyond approximately 3 AU. The IMF sector structure was generally not well‐developed during the period of this study. Notable differences were found between Voyager 1 and 2 observations. Differences in the region 1–2 AU are attributed to the substantially different latitudes of the two spacecraft during much of the period. Later differences are most likely associated with the fact that the Voyagers moved through the region between 4 and 5 AU at different times. Both Voyager 1 and Voyager 2 observed decreases with increasing heliocentric distance in the amplitude of ‘transverse’ fluctuations inBthat are consistent with the presence of predominantly undamped Alfvén waves in the solar wind, although not necessarily implying the presence of them. The presence of convective structures, compressive modes, and/or a saturated instability of Alfvén waves cannot be excluded by these Voyager results. Fluctuations in the strength ofB(relative to mean field strength) were found to be small in amplitude, with a RMS that is approximately one third of that for the transverse fluctuations, and they are essentially independent of distance

ISSN:0148-0227    

DOI:10.1029/JA087iA06p04345

年代:1982

数据来源: WILEY

摘要:

Energetic protons (0.5–20 MeV) appear to be trapped between a pair of shocks associated with the major solar flares of April 15 and April 28, 1978. Prolonged trapping (for a period of weeks) is implied by the large count rate enhancement and the large range of radial distances and longitudinal angles over which the trapping is observed. Shocks associated with both flares are detectable in the Pioneer 10 and Pioneer 11 plasma analyzer data. These shock/flare associations are different from those previously published by others studying the interplanetary events. The evidence for trapping has not been recognized heretofore most likely because of the unobservability of the April 15 flare (located ∼150°E of the sun‐earth line) and of the faintness of the signature in the plasma data of one shock in each pair. The apparent ability of a shock whose plasma signature is extremely weak to confine MeV protons in the outer solar system may have significant implications for cosmic ray studies. Contrary to earlier analyses of these data, the results of our analyses also imply significant azimuthal asymmetry in plasma and energetic particle behavior even at distances as far as 16 AU from the sun. The combination of these observations provides evidence for unexpectedly complex interactions in the outer solar system between energetic particles and solar wind

ISSN:0148-0227    

DOI:10.1029/JA087iA06p04354

年代:1982

数据来源: WILEY

摘要:

An analysis has been made of all the interplanetary shock wave disturbances detected with Los Alamos plasma instruments aboard IMP 6, 7, and 8 from 1971 through 1978. The study of the 103 forward shocks observed reveals that shocks occur preferentially during conditions of low proton temperature and speed and that the shell of shocked gas following shock passage is typically ∼0.14 AU thick. Helium enrichments (helium/hydrogen flux ratio ≥ 8%) are observed in association with 46% of the shocks. Shocks followed by helium enrichments (He shocks) are on the average the strongest shocks observed, in the sense that they exhibit the largest jumps in flow speed, temperature, and magnetic field strength and induce the largest geomagnetic response. The geometry of sampling the disturbances may account for the difference between He and non‐He shocks. There is a tendency for interplanetary shocks and helium enrichments to be part of complex, multiple events. This may result from multiple outbursts from the same solar active region. Usually the helium enrichment is found in plasma of higher than average field strength. Since helium enrichments are thought to identify the coronal material driving the shock, our observations support the conclusion that coronal ejecta originate in solar regions where the field strength is

ISSN:0148-0227    

DOI:10.1029/JA087iA06p04365

年代:1982

数据来源: WILEY

摘要:

The focus of this paper is two‐fold: (1) to examine how the presence of the spiral magnetic field affects the evolution of interplanetary corotating solar wind streams, and (2) to ascertain the nature of secondary large‐scale phenomena likely to be associated with streams having a pronounced three‐dimensional (3‐D) structure. The dynamics are presumed to be governed by the nonlinear, polytropic, single‐fluid, 3‐D MHD equations. Solutions are obtained with an explicit, Eulerian, finite differences technique that makes use of a simple form of artificial diffusion for handling shocks. For smooth axisymmetric flows, the picture of magnetically induced meridional motions previously established by linear models requires only minor correction. In the case of broad 3‐D streams input near the sun, inclusion of the magnetic field is found to retard the kinematic steepening at the stream front substantially but to produce little deviation from planar flow. For the more realistic case of initially sharply bounded streams, however, it becomes essential to account for magnetic effects in the formulation. Whether a full 3‐D treatment is required depends upon the latitudinal geometry of the stream. Where the stream front is sharply inclined to the equator or contains significant substructure, the 3‐D effects (the modifications to planar flow occasioned by the nonradial motions driven by the interaction) can exceed the magnetic effects. Conventional radial alignment tests may be incapable of distinguishing between 3‐D and temporal effects because the former need not be accompanied by readily identifiable north‐south flow signatures, for example. The shock surfaces predicted by the model can be quite oblique and can extend to latitudes beyond the north‐south boundary of the stream. Even with magnetic and 3‐D effects accounted for, however, shock formation in the model still occurs much closer to the sun than is generally observed. It is demonstrated how the systematic nonradial flow patterns seen about a stream interface can be used to infer the orientation of the stream front. Estimates of the latitudinal transport of angular momentum flux by stream fronts suggests that the effect is likely to be so large as to preclude accurate measurement of this quantity beyond about 0.5 AU. The 3‐D transport may have a discernible influence upon average magnetic field behavior, but steady corotating flows cannot produce the large north‐south field deflection

ISSN:0148-0227    

DOI:10.1029/JA087iA06p04374

年代:1982

数据来源: WILEY

摘要:

In addition to the published retarding potential analyzer (RPA) data that were taken in the Martian ionosphere, there exist many Viking RPA measurements of low‐energy (<75 eV) electron fluxes out to 16,000 km above the Mars surface. Both energy spectra and periods of continuous monitoring of the total flux above 15 eV are available. The mean electron current at energies greater than 15 eV increases monotonically by nearly 2 orders of magnitude from about 9000 km down to 700 km on Viking 1, but no clear signature of the bow shock is seen. The total wave power in the 2‐s measurement intervals for this current does, however, show a broad peak near 1700‐km altitude. The preshock variations in the low‐energy electron fluxes can be related to whistler mode oscillations in the solar wind plasma. It is concluded that there may be a highly turbulent shock structure that masks a clear signature of the bow shock in the time‐averaged data. The interaction model that is consistent with the bow shock at 1700 km, coupled with the ionosphere measurements, indicates that Mars is likely to have a permanent magnetic field adequate to stand off the solar wind during the Vikin

ISSN:0148-0227    

DOI:10.1029/JA087iA06p04395

年代:1982

数据来源: WILEY

摘要:

Magnetic field data from the geostationary satellites GOES 2 and GOES 3 are examined to study the development of substorm activity in the near‐earth nightside magnetosphere (around a radial distance of 6.6RE). Substorm events are those in which a well‐defined single onset is seen at low latitudes on the ground. The field configuration change from more taillike to more dipolelike starts initially in a longitudinally localized region in association with the ground onset, and it develops westward and eastward, even when the simultaneous onset of the low‐latitude positive bay is recorded in a wide longitudinal region on the ground. It is also found that the variation caused by the field‐aligned current starts at the ground onset and reaches a peak at the time of the field change. The present results are consistent with the view that a substorm is associated with a disruption and subsequent conversion of the cross‐tail current to the field‐aligned current connected with the polar ionosphere. It is indicated that the cross‐tail current near synchronous orbit and its disruption are important in producing the field configuration change at sync

ISSN:0148-0227    

DOI:10.1029/JA087iA06p04405

年代:1982

数据来源: WILEY

摘要:

It has been hypothesized by Lyons et al. that electrons in the slot region are precipitated by cyclotron resonance interactions with the plasmaspheric whistler mode wave bands. The energy spectra and the variations withLshell of the energy bands of the precipitating electrons have been found by Imhof et al. (1974) to be consistent with cyclotron resonance by waves in the few hundred Hz to few kHz range. Now, for the first time, simultaneous measurements have been made of the precipitating electron spectra, the wave frequency distributions, and the plasma density profiles. The electron measurements were performed from the P78‐1 low‐altitude satellite, whereas the wave and plasma density observations were made with the plasma wave experiment on the ISEE 1 spacecraft. Broad bands are often observed in the electron energy spectra with a well‐defined low‐energy cutoff that decreases in energy with increasingLvalue in a manner consistent with that calculated for first‐order cyclotron resonance with waves at the high‐frequency cutoff of the band. On the basis of the electron spectra from P78‐1 and the plasma densities obtained from the upper hybrid resonance frequencies measured on ISEE 1, the hiss cutoff frequencies are calculated for an assumed first‐order cyclotron resonance interaction and compared with the wave spectral density profiles measured on ISEE. Overall, the plasma wave and the electron measurements are consistent with each other, supporting the earlier hypothesis for the precipita

ISSN:0148-0227    

DOI:10.1029/JA087iA06p04418

年代:1982

数据来源: WILEY