摘要:

Detailed first estimates are presented of angular broadening in the outer heliosphere due to scattering of radio waves by density irregularities. The application is to the 2–3 kHz radiation observed by Voyager. Two plausible turbulence models, which account very well for scattering within 1 AU, are extrapolated beyond 10 AU. Both models predict significant angular broadening in the outer heliosphere, accounting semi‐quantitatively alone for the source sizes inferred from roll modulation data. Predictions are presented for radial variations in the apparent source size if scattering is important. Comparisons with available data argue that scattering is important (and indeed is the dominant contributor to the apparent source size) and that the radiation source is located in the outer heliosphere. Other evidence that scattering is important, such as the fluctuations in apparent source direction and intensity, are also identified. The effects of scattering should be included in future analyses of the 2–3 kHz emis

ISSN:0094-8276    

DOI:10.1029/95GL03331

年代:1995

数据来源: WILEY

摘要:

Recent Ulysses observations of millisecond spikes superposed on broader Langmuir wave packets in type III radio sources are compared quantitatively with constraints from the theory of wave collapse. It is found that both the millisecond spikes and the wave packets have fields at least 10 times too small to be consistent with collapse, contrary to previous interpretations in terms of this process. Several alternative explanations are considered and it is argued that the spikes should be interpreted as either non‐collapse phenomena or observational artifacts. To the extent the observations are representative, this rules out theories for type III bursts at ∼ 1–4 AU that rely on col

ISSN:0094-8276    

DOI:10.1029/95GL03513

年代:1995

数据来源: WILEY

摘要:

Extreme Ultraviolet Explorer satellite observations of Jupiter's Io plasma torus conducted over a two‐year time period before, during and after the impacts of comet Shoemaker‐Levy/9 reveal that no new spectral features appeared in the 400–715 Å spectral region. Io torus emission line luminosities remained stable to within ±20% and showed no strong coherent increasing or decreasing trend during the weeks preceding or following the impact events. This work supersedes our previous claims of possible luminosity changes to the torus derived from the same data (McGrath et al.,Science, 267, 131

ISSN:0094-8276    

DOI:10.1029/95GL03011

年代:1995

数据来源: WILEY

摘要:

The trajectories of ions in the Tsyganenko magnetic field model with a convection electric field have been compared to the trajectories when a perturbation electric field based on ISEE‐1 and Geotail observations of lower hybrid frequency waves is included. The inclusion of waves dramatically modifies the characteristics of the ion trajectories. For example, initial conditions which result in adiabatic orbits in the absence of waves are often non‐adiabatic when waves are included. In addition, both the regions of space accessible to the particles and the energization are changed. Although only individual trajectories were examined in this study, it is argued that the effect of the waves is to mix previously distinct regions of phase sp

ISSN:0094-8276    

DOI:10.1029/95GL03185

年代:1995

数据来源: WILEY

摘要:

When the interplanetary magnetic field turns southward, dayside reconnection leads to an increase of open magnetic flux and an increase of the electric potential drop across the polar cap. The enhanced electrostatic field in the ionosphere can be mapped to the closed field region of magnetotail, contributing to a dawn‐to‐dusk electrostatic component of electric field in the plasma sheet. In the presence of this driving electric field, an adiabatic evolution of the plasma sheet is formulated in A‐space, where A is the magnetic flux function. It is found that the adiabatic evolution leads to the observed enhancement of the entropy content in the near‐earth plasma sheet and to a tailward stretching of geomagnetic field lines. As a result, the cross‐tail current in the near‐earth plasma sheet is strong

ISSN:0094-8276    

DOI:10.1029/95GL03457

年代:1995

数据来源: WILEY

摘要:

It is shown that the presence of ionosphericO+ions in the inner central plasma sheet (ICPS) during growth phase of the substorms can excite nonresonant low‐frequency, long wavelength RH mode instability under certain conditions. For the ICPS parameters during enhanced convection events, the excited modes have real frequencies of (0.1–5.0) mHz, and the typical maximum growth rates of ∼ (0.1–4.0) mHz with corresponding wavelengths of ∼ (1–30)RE(REbeing the Earth's radius). The excited low‐frequency modes are expected to saturate to the maximum level of δB²/B0² ≈ (2.5 × 10−3−0.25), where δBand δB0are the fluctuating magnetic field associated with the unstable modes, and the equilibrium magnetic field respectively. The large amplitude magnetic field fluctuations due to the nonresonant low‐frequency instability driven byO+ions could twist the ICPS magnetic field into flux ropes, and also produce localised minima, in the magnetotail magnetic field near the neutral axis, which can be the potential sites for the excitation of the tearing mode

ISSN:0094-8276    

DOI:10.1029/95GL03427

年代:1995

数据来源: WILEY

摘要:

A diurnal variation in the infrared background radiation observed onSpacelab 2suggests that ion chemistry plays a part in the generation of those infrared emissions. Because water is the major contaminant in the environment of spacecraft in low earth orbit, it is thought to be the source of vibrationally excited and infrared active H2O+formed in O+(4S) + H2O charge‐transfer reactions. H2O+infrared luminescence spectra (0.01 µm FWHM) are calculated for the predicted nascent vibrational distribution as well as for steady‐state conditions assuming a charge‐transfer relative velocity of 7.8 km s−1, the low‐Earth orbital velocity. The calculated luminescence spectra exhibit an intense band between 3 and 3.5 µm, attributable to symmetric stretch deexcitation, and a minor band between 6 and 8.5 µm associated with bending vibrational transitions. The effect of charge‐transfer product rotational temperature, H2O partial pressure, and motional electric field on the infrared background spectra ar

ISSN:0094-8276    

DOI:10.1029/95GL03418

年代:1995

数据来源: WILEY

摘要:

VLF perturbations on signals propagating along great‐circle‐paths (GCP) through electrically active midwest thunderstorms are associated with luminous high altitude glows (referred to as sprites) observed from aircraft or ground. The data constitutes the first evidence that the physical processes leading to sprites also alter the conductivity of the lower ionosph

ISSN:0094-8276    

DOI:10.1029/95GL03507

年代:1995

数据来源: WILEY

摘要:

Fleeting columns of luminosity occurring above large thunderstorms at 50–90 km altitude, presently known as sprites, were imaged with an intensified video charge coupled device (CCD) camera during a July 1995 ground‐based campaign near Fort Collins, Colorado. These unfiltered intensified images reveal detailed spatial structure within the sprite envelope. The temporal resolution of standard interlaced video imagery is limited by the 60 fields per second acquisition rate (16 ms). The specific CCD used here, however, is subject to bright events leaking into the readout registers, allowing time‐resolution on the order of the linescan rate (63 µs). Typical sprite onset is found to follow the associated cloud lightning by 1.5 to 4 ms. The onsets of the individual sprites within a cluster are generally, but not always, simultaneous to within 1 ms. Sprites tend to have a bright localized core, less than 2 km in horizontal dimension, which rises to peak intensity within 0.3 ms and maintains this level for 5 to 10 ms before fading over an additional

ISSN:0094-8276    

DOI:10.1029/95GL03332

年代:1995

数据来源: WILEY

摘要:

Polar Mesospheric Summer Echoes (PMSE) have become a well known characteristic of radar backscatter from the summer mesopause regions in polar regions. The phenomenon has been observed at frequencies from 50 MHz to almost 1 GHz. In this paper we attempt to identify a space‐time manifold for the occurrence of PMSE. The resulting manifold, defined only by temperature, agrees well with observations and furthermore indicates when and where we might expect to observe PMSE in the futur

ISSN:0094-8276    

DOI:10.1029/95GL03481

年代:1995

数据来源: WILEY