摘要:

The in situ magnetic field and plasma measurements from the International Cometary Explorer (ICE) Mission obtained on September 11, 1985 are compared with CCD images of P/Giacobini‐Zinner (G‐Z) acquired with the 3.6 m Canada‐France‐Hawaii Telescope (CFHT) on Mauna Kea, Hawaii and a slit spectrogram from Lick Observatory during the same period. The CFHT image at ∼3.5 hr after the ICE encounter showed a short central ion tail with a diameter of ∼3 × 10³ km and a length of ∼2 × 104km as observed in the H2O+bandpass centered at 7025 Å. There was no distinct evidence of fine structure or ray activity. The Lick spectrogram of the H2O+emissions taken ∼0.5 hr post‐encounter with the slit perpendicular to the sun‐comet line showed an ion tail with a diameter of 1.2 × 104km. The ICE observations revealed a well defined 9.6 × 10³ km diameter magnetotail composed of two magnetic lobes in pressure equilibrium with a high beta central plasma sheet. These differing measures of tail width are found to be mutually consistent if the ion emissions observed at Earth originate in a slab‐shaped plasma sheet whose orientation is controlled by the direction of the interplanetary magnetic field. The results of this study also suggest that some thinning and thickening of cometary type I tails, usually attributed to plasma instabilities, may be due to changes in the angle at which the plasma sheet is vi

ISSN:0094-8276    

DOI:10.1029/GL013i011p01085

年代:1986

数据来源: WILEY

摘要:

We present magnetic field data from the cusp‐latitude South Pole station that exhibit, under appropriate local time and interplanetary magnetic field conditions, the signature expected in the ionosphere from a flux transfer event (FTE) at the magnetopause. In particular, the model of multiple X‐line reconnection at the magnetopause predicts field‐aligned currents in helical flux tubes, with transverse magnetic fields propagating as Alfvén waves toward the ionosphere. The distinctive magnetic signature at a polar cap magnetic station, particularly in the vertical component, can be used to infer the signs of the Byand Bzcomponents of the interplanetary magnetic

ISSN:0094-8276    

DOI:10.1029/GL013i011p01089

年代:1986

数据来源: WILEY

摘要:

A detailed analysis of electromagnetic fluctuations recorded during several magnetopause and boundary layer crossings by the ESA GEOS‐2 geostationary spacecraft is presented. A high level of electromagnetic (δE/ δB ∼ VA) fluctuations in the ULF (0 ‐ 10 Hz) range is observed for each such crossing. The obtained frequency spectra are shown to fit with a power law B² ∼ f−α. The distribution of these α indexes is found to be narrow (standard deviation ≲ 0.25 for 0.5 ≤ f ≤ 11 Hz), with a peak value α ∼ 2.5 which does not depend on the direction with respect to the magnetic field. Data suggest that the magnetopause boundary layer is the source of the

ISSN:0094-8276    

DOI:10.1029/GL013i011p01093

年代:1986

数据来源: WILEY

摘要:

We present a model for plasma transport in a rotation‐dominated magnetosphere (e.g., Jupiter) containing an internal plasma source (e.g., Io). We make a distinction between magnetic flux tubes filled with outward moving plasma and less dense flux tubes that move in to compensate. In the outer region where the heavier tubes are effectively isolated, their motion is described by a pair of coupled differential equations which have analytic solutions in the small velocity approximation. In a steady state, conservation of flux‐tube plasma content requires that the fraction of mass‐loaded flux tubes be a function of the radial outflow speed. Similar equations govern the motion in the inner region where heavy flux tubes predominate and lighter tubes are isolated. This raises the possibility of net outward radial transport even when the radial gradient of average flux‐tube content is positive. In the outer region where heavy flux tubes are isolated, the average steady‐state flux shell content decreases outward as the inverse square of radial

ISSN:0094-8276    

DOI:10.1029/GL013i011p01097

年代:1986

数据来源: WILEY

摘要:

A harmonic structure of compressional Pc5 oscillations during geomagnetically disturbed conditions is found in magnetic field data from the geostationary satellites, GOES 2 and 3. Compressional Pc5 pulsations sometimes show an interesting property that the compressional component oscillates with a frequency twice as high as that of the transverse component. In addition to these second harmonic events, waves with a transitional character between normal Pc5 waves and second harmonic events are also observed. In the normal Pc5 waves, the compressional component changes out of phase with the radial component in the northern equatorial region. In a transitional event, a small hump appears at the maximum phase of the radial component. These Pc5 oscillations with second harmonics dominant in the compressional component were observed mainly at GOES 3 and rarely at GOES 2 in the winter season. This occurrence pattern suggests that compressional Pc5 with harmonic structure is spatially confined to the equatorial region. It is also suggested that the particular modulation dominant in the compressional component reflects a finite amplitude effect in the inhomogeneity of the hot ring current plasma near the magnetic equator.

ISSN:0094-8276    

DOI:10.1029/GL013i011p01101

年代:1986

数据来源: WILEY

摘要:

The first satellite interferometric measurements of auroral kilometric radiation (AKR) were performed by cross‐correlating the waveforms detected by the ISEE 1 and ISEE 2 spacecraft. Such correlations were measured at 125 and 250 kHz for projected baselines perpendicular to the source direction ranging from 20 to 3868 km. High correlations were found for all projected baselines, with little or no tendency to decrease even for the longest baselines. These results must be interpreted differently for incoherent and coherent radiation. For incoherent radiation, the correlation as a function of the baseline is the Fourier transform of the source brightness distribution, and this implies an average source region diameter for all of the bursts analyzed of less than about 10 km. For such small source diameters, the required growth rates are too large to be explained by existing incoherent theories, strongly indicating that the radiation must be coherent. For coherent radiation, an upper limit to the source region diameter can be inferred instead from the angular width of the radiation pattern. The close similarity of the spectra at the longest baselines indicates that the angular width of the radiation pattern must be at least 2.5°, implying that the diameter of the source must be less than about 20 km. At present, the proposed closed‐loop radio lasing model is the only known mechanism for providing sources this s

ISSN:0094-8276    

DOI:10.1029/GL013i011p01105

年代:1986

数据来源: WILEY

摘要:

Waves with frequencies satisfying ω1+ ω2= Ω can heat ions. In this nonlinear interaction mechanism, coupling of a wave with frequency ω1and an ion trajectory, distorted by a wave with frequency ω2, results in a force varying at the gyrofrequency Ω at the ion position. The heating rate, verified by test particle calculations, is found for both broadband and coherent waves in the small gyroradius limit and is applied to ion conics above the auroral zone. This heating mechanism may be significant in other geophysical and astrophysical environ

ISSN:0094-8276    

DOI:10.1029/GL013i011p01109

年代:1986

数据来源: WILEY

摘要:

The acceleration of ionospheric ions transverse to the geomagnetic field by factors of 10³ is believed to be caused by plasma waves. We have made simultaneous measurements of electric fields (0‐16kHz) and energetic ions (50eV to 20keV) within regions of perpendicular ion acceleration from the sounding rocket MARIE. Perpendicular ion acceleration was correlated with plasma waves near and above the lower hybrid frequency. Ions were detected up to energies of 300 eV and the broadband lower hybrid waves reached an amplitude of 10‐30 mV/m (RMS) over the frequency band 4‐16 kHz. Although electric field amplitudes near the O+ cyclotron frequency reached a maximum value of 10 mV/m (RMS), there was no spectral evidence of electrostatic ion cyclotron waves associated with ion acceleration. There was spectral evidence of H+ Bernstein modes near the lower hybrid frequency. If we assume that whistler mode waves near and above the lower hybrid frequency were responsible for the ion acceleration then the conversion efficiency of wave energy to ion energy was .01

ISSN:0094-8276    

DOI:10.1029/GL013i011p01113

年代:1986

数据来源: WILEY

摘要:

Zonal drift velocity variations with 30% amplitudes and several minute time scales are observed in Jicamarca radar interferometer data collected from bottomside F region altitudes during two different periods with 70‐90 m/s and 100‐155 m/s mean zonal drifts. These fluctuations are indicative of intermediate scale vertical structuring of F region plasma to be expected in periods of Rayleigh‐Taylor bubble formation, and may contribute significantly to the decorrelation of forward scattered satellite signals detected for scintillation spaced receiver ana

ISSN:0094-8276    

DOI:10.1029/GL013i011p01117

年代:1986

数据来源: WILEY

摘要:

Rayleigh lidar observations of the molecule density in the upper stratosphere and the lower mesosphere using an XeF laser (351 and 353 nm) were made from April 1985 through March 1986, at Fukuoka, Japan (33.6°N, 130.4°E). The observed density profiles show the existence of waves with wavelengths around 10 km and downward phase velocities between about 0 and 1.2 km/h. In more than half of the cases, the induced wave periods are longer than the inertial period. Analysis shows that the zonal phase velocities of the waves go in the direction opposite to that of the background flow, at least in these cases. The phase velocity and amplitude of the waves show a semiannual variation. The height dependence of the averaged fluctuation amplitude indicates that the energy dissipation of the waves occurs in the observed altitude rang

ISSN:0094-8276    

DOI:10.1029/GL013i011p01121

年代:1986

数据来源: WILEY