摘要:

The rise in periapsis altitude with time has allowed the Pioneer Venus spacecraft to begin probing the subsolar Venus bow shock. This has allowed the altitude of the subsolar bow shock to be determined by in situ observations for the first time. The observed altitude of 2280 km at the nose together with the previously determined terminator altitude can be used to infer the shape of the obstacle using the gas dynamic model of the solar wind interaction with Venus. When this shape is compared to the measured locations of the Venus ionopause (defined as the point where the magnetosheath magnetic field pressure and ionospheric thermal pressures are equal), it is found that the observed ionopause position is too low to qualify as the obstacle. We infer that a layer of the mass loaded plasma in the magnetosheath forms the magnetic barrier.

ISSN:0094-8276    

DOI:10.1029/GL012i010p00627

年代:1985

数据来源: WILEY

摘要:

Using ISEE‐1 and 2 magnetometer data we have performed a survey of field‐aligned currents at the boundary of the plasmasheet between 10 and 22 Earth radii down the magnetotail. Most cases are observed as the plasma sheet expands across the spacecraft. We find that the currents are most often observed flowing earthward throughout this region of the tail; however, a fraction of the cases correspond to tailward flowing currents and these tend to be found dawnward of midnight. Toward dusk no tailward currents are found. The currents at the plasma sheet boundary should map to the high latitude boundary of the auroral zone, and consequently one might expect them to have a Region 1 polarity; just the opposite is observed. Typical sheet current densities for these cases are roughly 5 m

ISSN:0094-8276    

DOI:10.1029/GL012i010p00631

年代:1985

数据来源: WILEY

摘要:

A magnetohydrodynamic simulation of Kelvin‐Helmholtz instability at the magnetospheric boundary is performed by including inhomogeneities of plasma and magnetic field at the dayside low latitude magnetospheric boundary. A magnetopause current layer is corrugated highly nonlinearly by the instability and a wide velocity boundary layer is formed within the magnetopause current layer, a result being consistent with observations. Interchange of plasma and flux tubes is accomplished by the instabilit

ISSN:0094-8276    

DOI:10.1029/GL012i010p00635

年代:1985

数据来源: WILEY

摘要:

Recent observations show that extremely narrow emission lines are present in the spectrum of the terrestrial myriametric radiation, which on the basis of earlier observations has been characterized as nonthermal continuum radiation. The occurance of these monochromatic emissions is not predicted by previously published theories for the radiation. A linear instability, exciting low frequency electrostatic turbulence, is required by theories invoking a nonlinear coalescence to produce the radiation, but there are no conclusive observations associating low frequency electrostatic waves with the sources of myriametric radiation. In this study, the possibility that the radiation is produced by a nonlinear decay of electrostatic Bernstein waves with frequency near the upper hybrid frequency is considered. This mechanism can explain the narrow spectral lines, and does not require a linear instability at low frequencies.

ISSN:0094-8276    

DOI:10.1029/GL012i010p00639

年代:1985

数据来源: WILEY

摘要:

A new mechanism for exciting the kinetic ion cyclotron waves in the presence of a nonuniform electric field perpendicular to the external magnetic field is given. Application of this instability to various space plasmas is discussed. The new instability mechanism may provide a more efficient agent for perpendicular ion heating than other EIC generation processes, since the linear growth rate is insensitive to the temperature ratio.

ISSN:0094-8276    

DOI:10.1029/GL012i010p00643

年代:1985

数据来源: WILEY

摘要:

An ignition of Beam Plasma Discharge (BPD) in space was observed in a neutral gas‐electron beam interaction experiment by Space Shuttle/Spacelab‐1 in 1983. An electron beam of 8 kV 100 mA was injected into a high dense nitrogen gas cloud of 1023molecules which was released during 100 msec from the orbiter. The appearence of the beam and its surroundings observed by a low‐light‐level TV camera showed a local ignition of the beam plasma discharge in the gas cloud. The enhanced plasma production, generation of auroral emission and associated wave emission were also detected by onboard diagnostic inst

ISSN:0094-8276    

DOI:10.1029/GL012i010p00647

年代:1985

数据来源: WILEY

摘要:

The altitude variation of the Atmosphere Explorer optical glow intensity suggests that two different processes are responsible for the glow. One, dominant for altitudes above 180 km, has an emission brightness proportional to the ambient atomic oxygen density whereas the other, dominant at altitudes below 160 km, produces an emission whose intensity is proportional to the product of the densities of any of N2, O2or NO. The first mechanism apparently has two components, one from the surface recombination of O and H and the other from a process similar to that producing the Shuttle glow. Unless the efficiency of the second mechanism is much enhanced on the Shuttle its contribution to the Shuttle glow is negligible.

ISSN:0094-8276    

DOI:10.1029/GL012i010p00651

年代:1985

数据来源: WILEY

摘要:

Resonant lidar detection of neutral (Ca‐423 nm) and ionized ( Ca+‐ 393 nm) calcium altitude distributions has been performed during nighttime at the Observatoire de Haute‐Provence. The emitter is composed of two Nd‐Yag pumped dye lasers, the 393 nm emission being obtained by three waves mixing in a non‐linear crystal. The first detection of Ca has been carried out in December, 1982 and has shown that the integrated abundance of the atomic form is low, with a value of about 1.5 × 107cm−2, further confirmed by measurement performed in July, 1983. During this same month, the detection of Ca+has been achieved, proving the lidar ability to follow rapid evolutions of Ca+layers, which appear between 85 and 115

ISSN:0094-8276    

DOI:10.1029/GL012i010p00655

年代:1985

数据来源: WILEY

摘要:

The photolysis rate (J3) for CF2Cℓ2, (F‐12) in the stratosphere has been computed for three altitudes using measured solar fluxes from a balloon borne spectrometer. The rate is compared with that obtained by computing the attenuated flux using effective cross sections appropriate for the Schumann‐Runge bands (J1) [Allen and Frederick, 1982]. The result shows that the error in the F‐12 photolysis rate caused by using the Allen and Frederick approximation is about 10% (J1

ISSN:0094-8276    

DOI:10.1029/GL012i010p00659

年代:1985

数据来源: WILEY

摘要:

Solar absorption spectra from two stratospheric balloon flights have been analyzed for the presence of H2O2and HOCℓ absorption in the 1230.0 to 1255.0 cm−1region. The data were recorded at 0.02 cm−1resolution during sunset with the University of Denver interferometer system on October 27, 1978 and March 23, 1981. Selected spectral regions were analyzed with the technique of nonlinear least squares spectral curve fitting. Upper limits of 0.33 ppbv for H2O2and 0.36 ppbv for HOCℓ near 28 km are derived from the 1978 flight data while upper limits of 0.44 ppbv for H2O2and 0.43 ppbv for HOCℓ at 29.5 km are obtained from the 1981 fl

ISSN:0094-8276    

DOI:10.1029/GL012i010p00663

年代:1985

数据来源: WILEY