摘要:

In the previous studies correlatingE>10 MeV proton fluxes and spectra with various associated microwave burst parameters, the resulting high correlations were assumed to reflect a common acceleration process for the protons and the microwave‐emitting electrons. We suggest and test an alternative explanation for these correlations, which we term the big flare syndrome (BFS), that states that, statistically, energetic flare phenomena are more intense in larger flares, regardless of the detailed physics. Peak 1–8 Å X ray fluxes, characteristic of the thermal flare, are correlated with peak proton fluxes to derive correlation coefficients characteristic of the BFS. Of all microwave parameters tested for the 1973–1979 period, only the time‐integrated flux densities at 8800 and 15,400 MHz may be significantly larger than expected from the BFS. We fail to confirm previous results associating peak proton spectra with peak microwave spectral characteristics, thus finding no evidence that peak microwave fluxes are indicative of proton acceleration. We extend this conclusion to peak hard X ray correlations. The strongly nonlinear relationship deduced between flare energy and proton production also appears

ISSN:0148-0227    

DOI:10.1029/JA087iA05p03439

年代:1982

数据来源: WILEY

摘要:

The dynamics of small electrically charged dust grains within the rigidly corotating regions of planetary magnetospheres such as those of Jupiter and Saturn is considered. Depending on whether one is inside or outside the synchronous orbit, it is possible to have different populations of both positively and negatively charged particles moving in equilibrium circular orbits either in the prograde or retrograde sense. Not all these are stable, however, to small perturbations, such as would be produced by the gravitational tug of a neighboring satellite. The stable perturbed grains will perform a motion that can be described as an elliptical gyration about a guiding center which is in uniform circular motion. For different values of the specific charge, the ratio of the semiaxes of this ‘epicyclic’ ellipse lies between 1/2 and 1, while the gyration frequency ω of the grain about the guiding center lies between the Kepler frequency ΩKand ω0(which is the grain gyrofrequency in a nonrotating frame). In the environments of Jupiter and Saturn, where the grains are expected to be negatively charged both in the sunlit side and in the shadow and which move in the prograde sense, their guiding centers must have speeds intermediate to the Kepler speed and the corotation speed. Such particles with a unique specific charge (and therefore a specific size) could have a 1:1 magneto‐gravitational resonance with a neighboring satellite. A dispersion relation between ω and the wavelength λ of the perturbed orbits in the frame of the perturbed satellite has been derived. This result has been used to discuss the appearance and disappearance of the waves in theFring of Saturn elsewhere. We merely point out here that, while the existence of a single well‐defined wavelength implies a dust size distribution sharply peaked at a diameter of about 1 µ, the present theory also anticipates this situation. The only collisionless (and therefore nonevolving) state of small electrically charged dust grains moving in the same orbit is when they have precisely the same specific charge and therefore the same size (assuming the same density), since the electrical potential is the same

ISSN:0148-0227    

DOI:10.1029/JA087iA05p03449

年代:1982

数据来源: WILEY

摘要:

Energetic electron (energy higher than 2 MeV) observations by a synchronous satellite chain (which consists of GOES 2, GOES 3, and GMS covering the local time extent of approximately 10 hr) have been used to study the large‐scale characteristics of the dynamic behavior in the near‐earth magnetosphere for substorms, in which low‐latitude positive bay aspects are clearly seen in the ground magnetic data. Simultaneous multi‐satellite observations have clearly demonstrated the local time dependence of electron flux changes during substorms and the longitudinal extent of electron flux variations. Before a ground substorm onset the energetic electron flux decreases in a wide longitudinal region of the nighttime and the flux decrease is seen even on the afternoonside. For the flux behavior associated with the onset of the substorm expansion phase, there exists a demarcation line, the LT position of which can be represented as LT = 24.3 ‐ 1.5Kp. The flux shows a recovery to a normal level east of the demarcation line, and it shows a decrease west of the demarcation line. The region of the flux decrease during the expansion phase is restricted, and it is observed mainly on the afternoonside. The afternoonside flux decrease has a different characteristic from the nightside flux decrease preceding the expansion phase. The nightside flux decrease‐recovery sequence is observed in a wide region of more than 6 hr in the nighttime and the center of this variation exists in the premidnight region. It should be noted that the afternoonside flux decrease is not observed for every substorm and the nightside signature sometimes becomes a dominent feature even on the af

ISSN:0148-0227    

DOI:10.1029/JA087iA05p03456

年代:1982

数据来源: WILEY

摘要:

Energy spectra of precipitating electrons are fitted to the sum of three distributions: a power law, a Maxwellian, and a Gaussian. This fitting procedure determines seven parameters that characterize the essential features of each spectrum. These characteristic parameters are used to carry out various studies involving precipitating electrons. It is shown that the absence of the power law population from a particular spectrum is related to the softness of the precipitating primary flux, that the Maxwellian temperature and the Gaussian peak energy have a positive correlation, the strength of which varies with local time, that the upward moving Gaussian population has a loss cone distribution, and that the one‐dimensional velocity distribution parallel to the magnetic field occasionally displays a plateau or even a hump on the tai

ISSN:0148-0227    

DOI:10.1029/JA087iA05p03469

年代:1982

数据来源: WILEY

摘要:

Particle data from two geosynchronous satellites (Applied Technology Satellite 6 and SCATHA) show a normally hidden ion population appearing when the satellites are in the earth's shadow. Ion and electron data show the spacecraft potential dropping from +10 V in sunlight to +4 to +5 V in eclipse at local midnight, in low‐energy (Te<1 keV) plasma sheet environments. During eclipse, a cold (T = 1 eV), dense (n = 10–100 cm−3), isotropic ion population appears which was invisible in sunlight because of the larger positive spacecraft potential. Higher‐energy populations generally cover the tails of the hidden ion populations, so they cannot be inferred from daylight data. The isotropic population appears only in a few percent of the spacecraft eclipse events, appearing only at times of low Kp (2 or less, preceded by a day with Σ Kp ≤ 20). A low‐energy (T = 1–2 eV) field‐aligned population often appears with and without the isotropic population, at slightly higher flux levels. These fluxes are visible in sunlight, but again the distribution functions obtained in eclipse differ from those that would be inferred from daylight data. Measurement of the thermal plasma population on a consistent basis, particularly in the plasma sheet, will require some method of controlling the detector potential with respect to th

ISSN:0148-0227    

DOI:10.1029/JA087iA05p03481

年代:1982

数据来源: WILEY

摘要:

We have studied the response of the auroral eastward and westward electrojets and of the downward field‐aligned currents across the noon sector which feed them to southward turnings of the interplanetary magnetic field (IMF) and to substorm onsets in the nightside magnetosphere. We have found that while southward turnings of the IMF lead to electrojet intensifications and low‐level substorm activity, northward turnings of the IMF appear capable of triggering large substorm disturbances. Both northward and southward turnings of the IMF cause the downward field‐aligned current across the noon sector, as well as the auroral electrojets, to strengthen within a few minutes of the impact of the changed IMF at the magnetopause. Since large substorms involve the sudden release of energy stored in the magnetotail, we conclude that the tail current system links directly to the overall magnetosphere‐ionosphere current system involving the auroral electrojets. In this context a substorm associated with a northward turning of the IMF reflects a reconfiguration of the magnetotail in response to a change in the level of the solar‐terrestrial interaction involving a decrease in the rate at which solar wind energy penetrates into the magn

ISSN:0148-0227    

DOI:10.1029/JA087iA05p03489

年代:1982

数据来源: WILEY

摘要:

It is shown that Alfvén waves can be generated in the magnetosphere by the deceleration of magnetospheric convection due to the dynamo process in the magnetosphere‐ionosphere coupling. The growth rate of Alfvén wave packets bouncing between hemispheres is given by γ ≃ (2/µ0Σl) [αµ0²Σp²V0y² − 1] where α is a dimensionless constant (∼0.5), µ0is the free space permeability, Σpis the height‐integrated Pedersen conductivity,lis the field line length between hemispheres,V0yis the convection speed in the magnetospheric dynamo region. Alfvén waves become unstable under disturbed conditions when both ΣpandV0yare enhanced. The resulting unstable Alfvén waves can contribute to the Pi pulsations

ISSN:0148-0227    

DOI:10.1029/JA087iA05p03511

年代:1982

数据来源: WILEY

摘要:

Previous observations of magnetic pulsations in space have not been able to distinguish temporal from spatial structure unambiguously. Using the ISEE 1 and 2 spacecraft, satellites closely spaced in identical orbits, we are able to determine whether the observed amplitude variations are due to the motion of the spacecraft through a time stationary structure or are due to temporal changes in the wave. We have examined four dayside Pc 4, 5 period pulsations, three of which are observed betweenL= 4 and 7 within 10° of the magnetospheric equator. The resonant region widths of these three events range from ∼0.2–1.6Lshells. These are the first direct measurements of resonant region widths in space. For two of the three near‐equatorial events, plasma density data was available and indicated that the events are associated with gradients in the electron number density at the plasmapause. In one event, although waves are observed continuously by ISEE 2 during a portion of its inbound trajectory, at ISEE 1 there is a gap in the waves at the same time as a depleted density region is encountered. The gap in the waves can be explained as either a temporal or spatial effect, although the latter seems more likely. In addition to these observations we are able to use two independent techniques to determine the harmonic of two pulsation events. The first method compares the observed wave period with the period predicted by standing wave theory. The second method, which previously has been applied only indirectly, is to compare the phase of the observed wave electric and magnetic field. Alone neither of these methods can unambiguously determine the resonance harmonic. Here, using both methods together for the first time, we find that both events are second harmonic oscillations. This suggests that second harmonic oscillations are perhaps more common than previously t

ISSN:0148-0227    

DOI:10.1029/JA087iA05p03519

年代:1982

数据来源: WILEY

摘要:

A search has been carried out for magnetospheric line radiation in the VLF data acquired during the period October 1977–August 1979 by the Stanford University VLF receiver on the ISEE 1 satellite, while the satellite position varied between L = 2 and L = 8 and the satellite longitude lay in the range 50°W to 110°W. This magnetopsheric region encompassed the magnetic field lines linking three stations, Eights, Siple and Roberval, from which most ground‐based data on VLF line radiation has been obtained and also included one of the main regions in which the occurrence of VLF chorus has been actively linked to power line radiation. Line radiation was detected on only 5 of 90 orbits, and all examples occurred at frequencies below 4 kHz. The most clearly defined example of line radiation was acquired near L = 5 under conditions of very low magnetic activity during which the plasma‐pause was located at L ∼ 7. In this particular case, the strongest lines in the spectrum exhibited a frequency change of approximately 22 Hz/min over a 9‐min period, while weaker lines changed frequency as slowly as 6 Hz/min. The line radiation was detected during a period when whistler mode echoing was quite pronounced on lower L shells and may actually have been a scattered component of line radiation echoing between hemispheres on a magnetic shell of lower L value. In all instances the S/N ratio or the absolute intensity of the lines was quite low. Thus, in agreement with earlier work, we conclude that very little of the background VLF wave energy in the outer magnetosphere is contained directly in VLF line radiation. However, the catalytic role of line radiation in controlling VLF wave‐particle interactions remains t

ISSN:0148-0227    

DOI:10.1029/JA087iA05p03530

年代:1982

数据来源: WILEY

摘要:

Doppler‐shifted cyclotron resonance between electrons and narrowband whistler mode waves is employed in a new feedback model to account for observed signal growth and emission triggering in controlled experiments using the Siple Station, Antarctica, VLF transmitter. The interaction region (IR) is centered on the magnetic equator and is treated like an unstable feedback amplifier with a delay line. The temporal growth rate is given by γ = (G−1)/T, where G is the loop gain and T is the effective loop delay. For G1 the system is unstable and can generate self‐excited oscillations. The self‐excited oscillations reach saturation when G falls to unity, which occurs when the electron transit time through the interaction region is comparable with the phase bunching time. At signal levels well below saturation the model predicts exponential temporal growth. Saturation fields just inside and outside the plasmapause are estimated to be 1 mγ and 12 mγ, respectively, consistent with measurements. Because of a progressive loop phase shift the stimulated radiation can cancel the input signal at a certain point (located near the input to the IR) in time and space, giving rise to transient conditions resembling those at the tail‐end of the triggering signal. It is postulated that this temporary null may be the cause of emission triggering, and hence the region around this point is called the ‘trig

ISSN:0148-0227    

DOI:10.1029/JA087iA05p03537

年代:1982

数据来源: WILEY