摘要:

All spacecraft interact in some manner with the plasma environment in space, either the natural environment or a self‐induced environment. Early work on plasma spacecraft interactions focused on geosynchronous altitudes where the primary effect is spacecraft charging from the non‐Maxwellian high‐energy plasma environment. This work has been extensively reviewed. In the last several years, there have been a number of measurements in low Earth orbit (LEO) which, when combined with models, have revealed a rich variety of plasma interaction phenomena at these low altitudes. These are reviewed in this work. These include charging on polar orbits, ram and wake flows, use of high‐voltage power systems in space, arcing on high‐voltage solar arrays, noise generation in self induced plasma clouds around large, active spacecraft such as the shuttle, anomalous ionization of emitted neutral gases, use of electrodynamic tethers and plasma contactors and phenomena associated with the use of electrically propelle

ISSN:0148-0227    

DOI:10.1029/94JA03358

年代:1995

数据来源: WILEY

摘要:

In the summer and autumn of 1957 the author and his colleagues at the University of Iowa conducted 10 successful balloon‐launched rocket (rockoon) flights of Geiger‐Mueller tubes during two shipboard expeditions, one to the arctic and the other to the antarctic. Summit altitudes ranged from 77 to 130 km. One flight was conducted in the equatorial zone, six in the northern auroral zone, and three in the southern auroral zone. Detailed results of each flight are presented. Auroral bremsstrahlung was detected on eight of the nine high‐latitude flights. By virtue of physical shielding, the detectors were insensitive to photons of energyE8 keV, we find a typicale‐folding energyE*of about 10 keV for a differential photon number spectrum of the formdn/dE=Aexp(−E/E*) withAin units of photons (cm² s keV)−1. Essentially, the same value ofE*is obtained by two complementary methods: (1) The dependence of counting rate on atmospheric depthQand (2) the inverse ratio of counting rates of an “unshielded” tube and one with an added shield. A detailed discussion of the bases for interpretation of the flight data is given in an extended appendix. For a representative set of data (flight 64) we find an omnidirectional flux of downward moving photons of 2.4×104(cm² s)−1atQ= 0, the integral of the above spectrum fromE= 0 toE= ∞ with the explicit understanding that this result does not include the presumably much greater flux of photons havingE<8 keV and a much steeper spectrum. The corresponding electron number flux striking the top of the atmosphere is 9.3×107electrons (cm² s)−1with ane‐folding energyT*= 30 keV. The corresponding energy flux is 4.5 erg (cm² s)−1. Both of the two latter fluxes represent the integral from electron energyT= 0 toT= ∞ of the high‐energy tail of the electron spectrum, again with the explicit understanding that the estimates do not include the

ISSN:0148-0227    

DOI:10.1029/95JA01125

年代:1995

数据来源: WILEY

摘要:

Ion density, temperature, and the partial densities of the main constituents of the Venusian nightside ionosphere during moderate solar activity are presented. The data were measured by the retarding potential analyzer of the Pioneer Venus Orbiter during the entry phase of the mission in 1992. The highly variable plasma density is, on average, clearly reduced relative to that measured at high solar activity. A significant dawn‐dusk asymmetry, an excess of H+at dawn and O+at dusk, occurs in the postterminator sector. In the central nightside sector, beyond 150° solar zenith angle, the ionosphere is strongly depleted. The ion temperature distribution is similar to that measured during high solar activity, but the values are slightly smaller. The measurements indicate that the ion flux across the terminator, which is the dominant maintenance source for the nightside ionosphere at high solar activity, decreases with decreasing solar activity. At moderate solar activity we find that plasma transport and particle precipitation contribute approximately equally to the ionization of the central sect

ISSN:0148-0227    

DOI:10.1029/95JA01470

年代:1995

数据来源: WILEY

摘要:

We modeled the chemical and physical processes taking place in the nightside ionosphere of Venus by solving the one dimensional coupled continuity and momentum equations for 12 ion species [CO2+, O2+, O+, H+, NO+, CO+, N2+, N+, He+, C+, O+(²D) and O+(²P)]. We investigated the relative importance of the two major processes responsible for maintaining the nightside plasma densities: atomic ion transport from the dayside and impact ionization due to energetic electron precipitation. We compared our model calculations with electron density and ion composition observations obtained by instruments aboard the Pioneer Venus Orbiter during both high and moderate solar cycle conditions. These studies lead us to conclude that day‐to‐night atomic ion transport is dominant during high solar activity, while during moderate solar activity conditions the combined effects of the electron precipitation and reduced day‐to‐night ion transport are responsible for maintaining the nightside ionosphere

ISSN:0148-0227    

DOI:10.1029/95JA00331

年代:1995

数据来源: WILEY

摘要:

Acceleration or “pickup” of exospheric atomic oxygen ions by the interplanetary convection electric field is a generally accepted mechanism for the observed removal of O+from Venus. However, heavier escaping molecular ions (e.g., O2+, CO2+, N2+, CO+, and NO+) in high abundances were also detected in the wake by the Pioneer Venus Orbiter (PVO) neutral mass spectrometer (ONMS) operating in its ion mode. It was recently demonstrated that pickup of O+at low velocities from the terminator upper ionosphere could explain some characteristics of the Venus ionospheric “tail rays.” Since the PVO ion mass spectrometer data indicate that a significant molecular ion component also contributes to the terminator ionosphere above the collisional region (≥250 to 300 km altitude), we apply the tail ray model to study both the associated low‐altitude O+flows and the behavior of heavier ions of similar origin. The predicted flow vectors show dawn/dusk asymmetries similar to those in the ONMS observations. Further, the heavier ions achieve higher peak energies, thus improving their chances of detection by the ONMS which has an energy threshold of ∼36 eV in the spacecraft frame. The appeal of this explanation is that no exotic or complicated interpretations are required, and that a broad set of diverse observations fit a common scenario. The same mechanism could in principle be operating at Mars where molecular ions were also detected in the wak

ISSN:0148-0227    

DOI:10.1029/95JA00538

年代:1995

数据来源: WILEY

摘要:

We present the results of an analysis of Pioneer Venus Orbiter (PVO) plasma and electric and magnetic field data with evidence of a plasma transition along the flanks of the Venus ionosheath for 8 PVO passes near the terminator. This transition occurs between the bow shock and the ionopause and represents a stationary change in the properties of the shocked solar wind that streams around the Venus ionosphere. We find that the intermediate transition is characterized by three concurrent features: (1) A noticeable electric field burst measured with the 30 kHz channel of the electric field detector of the PVO; (2) a severe drop of the magnetic field intensity accompanied by a strong rotation of the magnetic field orientation to a direction closer to the Sun‐Venus axis in the inner ionosheath; and (3) substantially enhanced plasma fluxes detected at the time when these changes in the electric and magnetic fields are measured. The peak particle flux and the peak magnetic field intensity measured at this transition in the data of the 17 PVO orbits are also presented. It is found that large values of the enhanced particle fluxes occur mostly when the peak magnetic field intensity is larg

ISSN:0148-0227    

DOI:10.1029/95JA00329

年代:1995

数据来源: WILEY

摘要:

The DMSP F8 satellite's coverage of Earth's polar regions provides horizontal ion drift velocities along the dawn‐dusk meridian at approximately 835 km altitude in each hemisphere during the ∼100 min orbital period. We examine the ionospheric convection signatures observed by this spacecraft in the summer and winter hemispheres during periods when the interplanetary magnetic field (IMF) is directed northward for at least 45 min prior to the satellite entering the polar region and remains northward throughout the polar pass. These convection signatures can be readily categorized by the number of sunward and antisunward flow regions and by their potential distributions. Here we describe the most frequently identifiable and reproducible features of the convection pattern that exist during steady northward IMF conditions. In addition to IMFBz, the influences on the convection pattern of the IMFBz/|By| ratio, season, latitude, and solar wind velocity are all considered. The ratioBz/|By| provides a first order organization of the signatures that occur on the dayside of the dawn‐dusk meridian. Sunward flow at highest latitudes on the dayside of the dawn‐dusk meridian is the dominant feature seen in the large‐scale convection signature during steady northward IMF; however, sunward flow at highest latitudes does not imply the existence of a particular number of convect

ISSN:0148-0227    

DOI:10.1029/94JA03318

年代:1995

数据来源: WILEY

摘要:

The Argon Release for Controlled Studies (ARCS) 4 sounding rocket was launched northward into high altitude from Poker Flat Research Range on February 23, 1990. The vehicle crossed geomagnetic field lines containing discrete auroral activity. An instrumented subpayload released 100 eV and 200 eV Ar+ion beams sequentially, in a direction largely perpendicular to both the local geomagnetic field and the subpayload spin axis. The instrumented main payload was separated along field lines from the beam‐emitting subpayload by a distance which increased at a steady rate of ∼2.4 m s−1. Three‐dimensional mass spectrometric ion observations of ambient H+and O+ions, obtained on board the main payload, are presented. Main payload electric field observations in the frequency range 0–16 kHz, are also presented. These observations are presented to demonstrate the operation of transverse ion acceleration, which was differential with respect to ion mass, primarily during 100‐eV beam operations. The preferential transverse acceleration of ambient H+ions, as compared with ambient O+ions, during the second, third, fourth, and fifth 100‐eV beam operations, is attributed to a resonance among the injected Ar+ions, beam‐generated lower hybrid waves, and H+ions in the tail of the ambient thermal distribution. This work provides experimental support of processes predicted by previously published theory

ISSN:0148-0227    

DOI:10.1029/94JA03238

年代:1995

数据来源: WILEY

摘要:

The recent availability of the new EUVAC (Richards et al., 1994) and EUV94X (Tobiska, 1993b, 1994) solar flux models and new wavelength bin averaged photoionization and photoabsorption cross section sets led us to investigate how these new flux models and cross sections compare with each other and how well electron densities (Ne) calculated using them compare with actual measurements collected by the incoherent scatter radar at Millstone Hill (42.6°N, 288.5°E). In this study we use the Millstone Hill semiempirical ionospheric model, which has been developed from the photochemical model of Buonsanto et al. (1992). For theF2 region, this model uses determinations of the motion term in theNecontinuity equation obtained from nine‐position radar data. We also include two simulations from the field line interhemispheric plasma (FLIP) model. All the model results underestimate the measuredNein theEregion, except that the EUV94X model produces reasonable agreement with the data at theEregion peak because of a large Lyman β (1026 Å) flux, but gives an unrealistically deepE‐F1 valley. The ionospheric models predict that the O2+density is larger than the NO+density in theEregion, while numerous rocket measurements show a larger NO+density. Thus the discrepancy between the ionospheric models and the radar data in theEregion is most likely due to an incomplete understanding of the NO+chemistry. In theF2 region, the photoionization rate given by EUV94X is significantly larger than that given by the EUVAC and earlier models. This is due to larger EUV fluxes in EUV94X compared to EUVAC over the entire 300‐1050 Å wavelength range, apart from some individual spectral lines. In the case of EUVAC, this is partly compensated for by larger photoelectron impact ionization due to the larger EUV fluxes below 250 Å. The differences between ionospheric model results for the different cross‐section sets are generally much smaller than the differences

ISSN:0148-0227    

DOI:10.1029/95JA00680

年代:1995

数据来源: WILEY

摘要:

A time‐dependent three‐dimensional computer simulation of equatorialFregion ionosphere has been carried out to understand the electron temperature structure observed by Hinotori satellite in the low and middle ionosphere. This model provides three‐dimensional distributions of ion densities, electron temperature, and ion temperatures. The simulations showed the electron temperature enhancements around the equator in the morning, in the midlatitude in the afternoon, and around the equatorial anomaly region from afternoon to midnight. The enhancements in the morning are due to photoelectron heating. The afternoon enhancements in the midlatitude come from the balance of heating and cooling. When no meridional neutral wind is included in the simulation, the electron temperature did not show remarkable enhancements in the midlatitude in the afternoon because of strong cooling by the dense electron density. Around the equatorial anomaly region the electron temperature increased at high altitude in the evening because of the competing effects of plasma cooling and the plasma movements. Since the ionospheric plasma zonalE×Bdrift is eastward near the sunset (whereEis ionospheric electric field andBis magnetic field) and the vertical drift is downward, the high‐altitude dayside hot plasma can enter into the topsideFregion in the premidnight. The computer simulations were directly compared with the Hinotori satellite data. The simulation results were consistent with the equatorial electron density and temperature observed by the Hinotori s

ISSN:0148-0227    

DOI:10.1029/95JA01356

年代:1995

数据来源: WILEY