摘要:

We have systematized and recorded our study of the phase of the 10‐hour modulation of energetic electrons seen by Pioneers 10 and 11 in the Jovian magnetosphere. To start with, we focus on the peaks rather than the valleys of each cycle because the peaks are where physically interesting features occur, such as particle acceleration, current sheets, etc. To identify the peaks, we demand that the instantaneous intensity be higher than the 5‐hour running average and the 5‐hour running average be greater than the 10‐hour running average. These criteria select an interval rather than a point and we feel that this interval is an appropriate estimate of the experimental uncertainty. When the phases of the peaks are plotted together, they create patterns which we discuss in terms of disk‐like, clock‐like, and rotating anomaly models of the magnetosphere. Each model fits some of the data, but no model explains all of the data convincingly. We conclude that we still do not understand the configuration of the outer Jovian ma

ISSN:0148-0227    

DOI:10.1029/JA084iA10p05763

年代:1979

数据来源: WILEY

摘要:

We analyze features of particle behavior in magnetospheric convection using simple analytic forms for the electrostatic potential which have been used in other recent works. We show that analytic approximations for the shape and position of surfaces delimiting closed and open particle orbits can be derived. These approximations are good for any pitch angle and at most energies. They break down only for the medium‐energy protons that are predicted by such models to penetrate far inside the plasmapause. The expressions we derive allow rapid tests of a variety of electric field models when analyzing particle data, and we illustrate this by intercomparing field models with several observation

ISSN:0148-0227    

DOI:10.1029/JA084iA10p05773

年代:1979

数据来源: WILEY

摘要:

Energetic (keV) protons and 0+ions with field aligned pitch angle distributions and peak fluxes up to ∼ 7 × 107(cm² s sr keV)−1have been observed streaming downward in the high altitude (∼ 1RE) auroral ionosphere. In two examples described in detail, the correlations observed between the downward flowing and coincident trapped ion populations suggest a common origin. Downward flowing ion events are a much less frequent phenomenon than upward flowing ion events in the auroral region. The significant difference implies that the energetic upward flowing ions from the auroral ionosphere are commonly injected into the trapped population of the plasma sheet, and furthermore that parallel electric fields involving potential drops of ≳500 V are directed preferentially upward in the altitude range from 2000 km to ∼ 3RE. Spatially localized regions of enhanced hot (∼keV) plasma density were frequently observed in the lowLportion of the plasma sheet. The statistical location of these ‘plasma clouds’ correlates well with the substorm injection boundary near dusk inferred by McIlwain (1974) and with the upward flowing ion events observed at ∼ 1REaltitude (Ghielmetti et al., 1978a, b). The downward flowing ion events occurred preferentially within such ‘plasma clouds.’ The results described in this paper suggest that upward flowing ions from the auroral acceleration regions are responsible for both the downward flowing ions and for at least some of the plasma clouds. A significant fraction of the equatorial substorm injected plasma clouds may thus result from this io

ISSN:0148-0227    

DOI:10.1029/JA084iA10p05781

年代:1979

数据来源: WILEY

摘要:

Vertical drift measurements have been made at Jicamarca for more than half a solar cycle. The data from periods of high and low activity are appreciably different. Daytime drift velocities during sunspot minimum are usually larger than during the maximum, while the opposite is true for nighttime periods. The evening reversal occurs earlier during sunspot minimum than during the maximum, but the morning reversal is not altered. The period of eastward electric field (upward drift) is thus shortest during sunspot minimum and local winter. By integrating the drift velocity data with respect to time, one can obtain a measure of the total potential drop between reversal points (near the terminators). This drop is largest at solar maximum. There is also a pronounced seasonal variation, with a minimum in mid‐December during both solar minimum and maximum. The general features of the data cannot be explained solely on the basis of tidal winds driving anEregion dynamo; polarization fields related to theFregion dynamo are of major importance, particularly in helping to explain the enhancement of the daytime upward drift which often occurs shortly before the drift reverses to downward in the evening. In order to account quantitatively for the observed variations, however, numerical models considerably more sophisticated than those presently available are neede

ISSN:0148-0227    

DOI:10.1029/JA084iA10p05792

年代:1979

数据来源: WILEY

摘要:

Radar measurements ofEandFregion drift velocities have been used to look for correlations between changes in equatorial electric fields and the interplanetary magnetic field (IMF). The east‐west component of the IMF appears to be unimportant, but the north‐south component has some effect; rapid reversals from south to north are sometimes correlated with reversals of the equatorial east‐west electric field during both daytime and nighttime. This is not always true, however, the IMF may reverse without any apparent effect at the equator. Furthermore, large equatorial field perturbations are sometimes observed when the IMFBzis large and southward but not varying drastically. In this latter case the equatorial perturbations start nearly simultaneously with the onset of auroral substorms, while in the previous case they usually correlate with the onset of the substorm recovery phase. These observations indicate that the IMF does not affect the equatorial electric fields directly. Rather, it is changes in the magnetospheric electric fields and the auroral zone electric field and conductivity distribution (which may or may not be triggered by IMF changes) which alter the worldwide ionospheric current flow and electric field pattern, of which the equatorial observations are an indic

ISSN:0148-0227    

DOI:10.1029/JA084iA10p05797

年代:1979

数据来源: WILEY

摘要:

Simultaneous auroral and equatorial electric field data are used along with magnetic field data to study anomalous electric field patterns during disturbed times. During some substorms, accompanied by ring current activity, the worldwide equatorial zonal electric field component reverses from the normal pattern. This is interpreted as a partial closure of high latitude field aligned currents in the dayside, low latitude ionosphere. These currents flow westward across the dayside. In several cases the zonal equatorial electric field component was nearly identical in form to the zonal auroral component, indicating the close electrical coupling between these regions. Less certain, but equally intriguing, is the evidence presented for a close relationship between the zonal equatorial electric field and the time derivative of the ring current induced magnetic field. Another class of events seems related to rapid changes of magnetospheric convection and a temporary imbalance between the field external to the plasmasphere and the shielding charges in the Alfven layer. Examples of both rapid increases and decreases are presented. The latter seems often to be related to a northward turning of the interplanetary magnetic field.

ISSN:0148-0227    

DOI:10.1029/JA084iA10p05803

年代:1979

数据来源: WILEY

摘要:

The magnitude of the strong flow of 1.79–2.15 MeV protons away from the Jovian magnetic equator is used to estimate the residence lifetimes of these protons in the equatorial source region. The lifetime is approximately 1.2 × 105/(R− 5.8)² s, whereRis distance in Jovian radii from Jupiter's center to the equatorial region of interest. At Europa and Ganymede (but not at Io) this lifetime is 1–2 orders of magnitude shorter than sweepup lifetimes by the moons. The fluxes of these protons, integrated over the observed range from 6 to 40 Jovian radii, amount to 3 × 1023particles per second, per degree of longitude and carry away about 9 × 1017ergs per second p

ISSN:0148-0227    

DOI:10.1029/JA084iA10p05813

年代:1979

数据来源: WILEY

摘要:

The implications of southward magnetic fields at the magnetotail neutral sheet to the development of streaming anisotropy of energetic electrons and magnetospheric substorm activity are examined. Magnetic field and energetic particle measurements from the Imp 6 spacecraft, theAEindex, and global auroral images from DMSP spacecraft are utilized in this study. Criteria are developed to identify events of southward magnetic fields at the neutral sheet which imply the presence of X‐type magnetic neutral lines. Several features of the observations suggest that the southward magnetic fields and the implied X‐type neutral lines are associated with magnetic bubbles in the neutral sheet region. It is found that the signatures of magnetic bubbles are sometimes detected in association with tailward streaming and flux enhancement of energetic electrons (47 keV

ISSN:0148-0227    

DOI:10.1029/JA084iA10p05817

年代:1979

数据来源: WILEY

摘要:

A synoptic study of electric wave, magnetometer, and plasma data from Imp 6 has been carried out for times when banded electrostatic waves are observed between harmonics of the electron gyrofrequency in the earth's outer magnetosphere. Four separate classes of such waves have previously been identified by us. The spatial and temporal occurrences of waves in each class are summarized here, as are correlations of occurrence with geomagnetic activity. Most importantly, associations between the observations of waves of different classes and the relative portions of cold and hot electrons present at the position of the spacecraft are established. The cold to hot ratio varies in accordance with the predictions of our previous theoretical work, which models the emission as arising unstably from a hot loss cone distribution existing simultaneously with a cold isotropic electron component. Finally, evidence for the signature of the loss cone is sought in the plasma data.

ISSN:0148-0227    

DOI:10.1029/JA084iA10p05828

年代:1979

数据来源: WILEY

摘要:

The existence of monochromatic structures in ULF or VLF magnetospheric emissions has often been questioned, and in some cases it has been demonstrated that the apparent frequency structure of these emissions was due to the method of analysis. We present here a theoretical study of the apparent frequency‐time structures which should result from different frequency analysis techniques applied to two kinds of signals. Signals of type I consist of two or more gliding tones (whose frequency varies linearly with time) closely spaced in time. Type II signals consist of two or more quasi‐monochromatic emissions of finite duration, slightly displaced in frequency and time. We show that when very narrow or very wide filter bandwidths are used, similar frequency‐time patterns may be obtained with both signals. These patterns are described, as a function of the characteristics of both the signal and the filter. A procedure is suggested which consists of analyzing the same signal with different filter bandwidths and which enables one to distinguish between type I and type II signals in most cases. The validity of the theory is checked on computer‐simulated wave forms. Application is also made to natural magnetospheric emissions recorded both on the ground and on board satellites. It is shown that whereas the Pc 1 fine structure seems to be a real effect, there is no clear evidence that chorus VLF emissions do present a banded st

ISSN:0148-0227    

DOI:10.1029/JA084iA10p05839

年代:1979

数据来源: WILEY