摘要:

The large‐scale structure of flare‐associated interplanetary shocks is investigated by examining the properties of 116 shocks which originated in solar flare events during a 18.7‐year period commencing mid‐May 1967. The best average representation of these shocks is an expansion which is uniform over about 100°. The highest compression ratio across the shock (∼2.7) is about 15° west of the radial from the flare site. The loose coupling of shocks and their drivers is supported by the observation that drivers are generally only detected for shocks originating near central meridian. A comparison of the numbers of shocks per year with the numbers of sudden commencement geomagnetic storms indicates that the percentage of shocks at 1 AU which originate in flare events is less than 50%. Many shock‐flare associations made in the past are prob

ISSN:0148-0227    

DOI:10.1029/JA093iA01p00001

年代:1988

数据来源: WILEY

摘要:

The theoretical model of Tu et al. (1984) describing the radial variation of the power spectra of interplanetary Alfvénic fluctuations has been extended to explain the radial variations of Alfvénic fluctuations between 0.3 and 5 AU and of the solar wind proton temperature observed by Helios between 0.3 and 1 AU. The extended model predicts that the fluctuations have the following features. (1) If the lifetime of two wave packets in the fluctuations is less than their correlation time, their interaction time is determined by the lifetime. In this case, the spectral index in the high‐frequency range is close to −5/3. (2) The shape of the power spectrum evolves as the fluctuations propagate away from the Sun in the distance range between 0.3 and 1 AU; however, it remains approximately unchanged between 1 and 5 AU. The extended model also predicts that the proton magnetic moment increases with increasing heliocentric distance and that this increase for high‐speed streams from 0.35 to 0.95 AU is about 2×104K/nT. All these results are consistent with observations, indicating that the extended model proposed in the present paper can account for both the damping of Alfvénic fluctuations and the heating of the solar wind protons simultaneously. A relationship between the thermal speed of solar wind protons and the variance of the solar wind velocity components is also predicted for further comparison of the present model with He

ISSN:0148-0227    

DOI:10.1029/JA093iA01p00007

年代:1988

数据来源: WILEY

摘要:

Analysis of the Pioneer 10 and rocket observations of disk averaged emission from the sunlit atmosphere of Jupiter indicates that the spectrally integrated EUV brightness was reduced by at least a factor of 2 relative to Voyager spacecraft observations in 1979. Most of the variation is caused by theHLyα component in the spectrum, which was reduced ≈ 1 order of magnitude near the time of solar minimum in 1972‐1973. Although the analysis of the data does not produce entirely consistent results, the weight of evidence points to a factor of order ≈ 2 lower abundance of H in Jupiter's atmosphere in 1972–1973 relative to 1979. The low emission rate inHLyα near the time of solar minimum in this proposed scenario is caused by an electroglow energy deposition rate reduced by a factor of ≈ 3. The apparent reduced abundance of H implies a reduced thermospheric temperature, even under the assumption of a constant electroglow depo

ISSN:0148-0227    

DOI:10.1029/JA093iA01p00021

年代:1988

数据来源: WILEY

摘要:

Observations monitoring the long‐term spatial and temporal behavior of the Jovian H I Ly α emission have been made with the International Ultraviolet Explorer (IUE) observatory beginning in December 1978, and extending through December 1986. The hydrogen bulge region centered near λIII= 100° has been observed to be a persistent feature of the Jovian upper atmosphere throughout the period of the observations, which includes the maximum of solar cycle 21 and the current minimum in solar activity. New and previously unpublished measurements made since early 1982 show that the average brightness of both the bulge and nonbulge regions has varied with the long‐term solarLyα output, which has decreased by a factor of ∼ 2 in this time frame. However, the bulge is ∼ 25% brighter on average and exhibits more short‐term variability than the nonbulge region. The factor of ∼ 2 change in Jupiter's Ly α brightness during the descending phase of solar cycle 21 is significantly less than the order of magnitude variability reported for the ascending phase of the same cycle. The IUE results are consistent with pure resonant scattering from an H column of ∼1017cm−2and indicate that no observable changes have taken place in the Jovian atomic hydrogen abundance or the average atmospheric conditions during the 8‐year period since December 1978. If the electroglow process recently proposed for the outer planets plays a significant role in the long‐term behavior of the Jovian Ly α emission, the electroglow must also follow the solar cycle at Ly α. Finally, as a result of revisions in both the IUE instrumental sensitivity at Ly α and the dimensions of the spectrograph large aperture, there is no significant difference between Voyager and IUE measurements of the Jovian Ly α brightness made within the same time frame and with approxim

ISSN:0148-0227    

DOI:10.1029/JA093iA01p00029

年代:1988

数据来源: WILEY

摘要:

One of the most interesting results of the cometary flyby missions was the realization that magnetohydrodynamic turbulence generated by the pickup process of freshly ionized cometary particles results in fast pitch angle scattering of the newly implanted ions. This process rapidly modifies the newly implanted ion pitch angle distribution in the solar wind frame of reference, from the original pickup ring to a pickup shell distribution. It also appears that the implanted ions have an isotropic pitch angle distribution in the decelerating solar wind frame of reference. This paper presents a self‐consistent description of the multispecies plasma flow (composed of solar wind protons and cometary H+and O+) in the unshocked upstream region. The solar wind is treated as a fluid, while the evolution of the implanted ion distributions is described by generalized transport equations. The ambient solar wind population is depleted by charge exchange, while implanted protons and oxygen ions are produced by photoionization and charge transfer and lost by charge exchange. The transport equations take into account the adiabatic velocity change due to the deceleration of the flow, velocity diffusion, charge exchange loss, and the pickup of newly created ions. The model equations were numerically solved for the comet Halley flyby conditions, and the results are compared with spacecraft observations. Our calculations imply that second‐order Fermi acceleration can explain the implanted spectra observed in the unshocked solar wind. The comparison of the measured and calculated distribution functions also indicates that spatial diffusion (and consequently first‐order Fermi acceleration) of implanted ions is likely to play an important role in forming the energetic particle environment in the vicinity of the

ISSN:0148-0227    

DOI:10.1029/JA093iA01p00035

年代:1988

数据来源: WILEY

摘要:

We have studied electromagnetic wave instabilities fed by coexisting newborn (cometary) hydrogen and oxygen ions, illustrating the modifications encountered in the unstable dispersion topology as the relative orientation of the interplanetary magnetic field and the solar wind velocity is varied, discussing the free energy sources, and assessing the influence of the newborn particle density and temperature. Utilization of generalized Brillouin diagrams clarifies the physical nature of new left‐hand polarized, costreaming modes excited by the newborn heavy ions and nonoscillatory, purely growing structures (unrelated to the mirror wave) generated by the two newborn ion species. Although the newborn protons stimulate resonant instabilities more efficiently in ion‐rich environments, the hierarchy of wave growth changes as the ion densities decrease (increasing distance from the comet). Larger growth rates for modes associated with the heavy‐ion beam may then occur. The interaction between the two coexisting ions is generally weak: each beam excites resonant instabilities without undue influence from the other newborn ion species in most dispersion domains. Cometary environments suggest the parameters of the adopted model, but the results are helpful in the interpretation of other observations of low‐frequency wave activity i

ISSN:0148-0227    

DOI:10.1029/JA093iA01p00048

年代:1988

数据来源: WILEY

摘要:

Through a further application of the condition for magnetospheric wave growth in the presence of anisotropic charged‐particle distributions, the Kennel‐Petschek theory that traditionally imposes an upper bound on the integral flux of charged particles at energies above a certain threshold is extended to provide a limit on the differential flux at any energy above this threshold. Thus, a modest reformulation of the nonrelativistic Kennel‐Petschek problem for electrons and protons enables a limiting energy spectrum to be derived, such that (for specified pitch‐angle anisotropysof the energetic particle population) electromagnetic‐cyclotron waves at each frequency less than a fractions/(s+ 1) of the equatorial gyrofrequency are marginally stable against spontaneous generation. The limiting spectrum is given in closed form for integer values ofs(>0) and computed numerically or by analytical interpolation for non‐integer values ofs. Asymptotic expansions for energiesEbarely above and much greater than the minimum resonant energyE* provide estimates of the limiting energy spectrumJ4π*(E) in these extremes, regardless of whethersis an integer. A reconsideration of the original Kennel‐Petschek problem, in which the differential energy spectrum is not calculated but specified as a certain power law (J4π∝E1‐l), enables both the wave frequency ω*/2π corresponding to maximum spatial growth rate and the limiting integral fluxI4π*above the minimum resonant energyE* to be calculated in closed for

ISSN:0148-0227    

DOI:10.1029/JA093iA01p00059

年代:1988

数据来源: WILEY

摘要:

The Lockheed high‐energy particle spectrometer on the SCATHA satellite, P78‐2, occasionally measures energetic electron fluxes near synchronous altitude that exceed the commonly cited Kennel and Petschek trapping limit. Twelve cases have been analyzed in detail, including several from relatively quiet times and from times when the spectrum became very hard. These were compared with an energy‐dependent formulation of the trapping limit (Schulz and Davidson, this issue), which predicts a steeply descending spectrum above the minimum resonant energy for wave growth, and a 1/Espectrum at high energies. The spectrometer permits pitch angle resolution fine enough to resolve the loss cone and to derive the anisotropies that were needed to make the comparisons with the theory. In all the cases examined, over a wider range of conditions, there is a region of the spectrum, often less than a decade wide in energy, that matches the theoretical spectrum. The plasma densities derived from the fitting of ideal theoretical spectra to the measured spectra were compared with ion densities determined from the University of California, San Diego, ion spectrometer aboard the SCATHA satellite. The agreement between the two independent determinations of the plasma density supports an interpretation of the energetic electron spectra based on the occurrence of flux limiting during the events analyzed. It is concluded that flux limiting may be active much of the time over some portion of the electron spectrum, and that the overall spectrum exhibits greater variability than can be simply explained by steady state flux limiting alone. The results are consistent with a model in which the limiting process takes place in sporadic precipitation events, punctuated by intervals of weak diffusion. Numerical estimates of the energy‐integrated flux above the minimum resonant energy agree well with the Kennel and Petschek prediction. A new empirical energy‐integrated flux limit ofI* ≈ 2 × 1011/L4electrons cm−2s

ISSN:0148-0227    

DOI:10.1029/JA093iA01p00077

年代:1988

数据来源: WILEY

摘要:

We demonstrate that there are distinct differences in the electron precipitation patterns (or the polar cap size), geomagnetic activity, and field‐aligned currents in the highest‐latitude region for small and large IMFBzvalues when the IMFBzcomponent is positive. First, during periods of weakly northward IMF, there is a distinct area in the highest‐latitude region in which the electron precipitation is absent except for the polar rain. By contrast, during strongly northward IMF, the entire polar region is often filled with burst‐type soft electron precipitations. Second, geomagnetic disturbances and field‐aligned‐current intensitites in the highest‐latitude region (>80° in geomagnetic latitude) are less during a weak IMFBzcondition than those during a strongly northward IMFBzcondition. Geomagnetic activity in the auroral zone for both conditions is absen

ISSN:0148-0227    

DOI:10.1029/JA093iA01p00097

年代:1988

数据来源: WILEY

摘要:

Using data from the high‐altitude plasma instrument on board the DE 1 spacecraft, we have estimated the perpendicular (to the magnetic field) extent of the region of ion injection into the cusp by measuring the energy dispersion of the ion V‐shaped signatures seen on energy‐time spectrograms. Three different passes were chosen based on the clarity of the V‐shaped ion signatures. These studies indicate that the injection region has a dimension perpendicular to the magnetic field in the range 1000 km

ISSN:0148-0227    

DOI:10.1029/JA093iA01p00105

年代:1988

数据来源: WILEY