摘要:

It has been suggested byRichardson et al.[1995] that the solar wind shows signs of deceleration due to mass‐loading by interstellar pickup ions. They based their conclusion on observations from the Voyager 2 and IMP 8 spacecraft. Observations from the Pioneer Venus Orbiter (PVO), IMP 8, Voyager 2, and Pioneer 10 spacecraft are compared to look for this deceleration. While these comparisons suggest the possibility of deceleration at Voyager 2, the magnitude of this deceleration appears to be significantly less than the deceleration reported byRichardson et al.[1995]. Some of this difference could be explained by a north‐south asymmetry in solar wind speed during solar cycle 21. The implications of these results are discussed, along with possibilities for further investigati

ISSN:0094-8276    

DOI:10.1029/95GL02469

年代:1995

数据来源: WILEY

摘要:

Mean density and temperature gradients of solar wind protons and α particles are derived from SWICS/Ulysses observations between 1.2 and 5.4 AU in the ecliptic plane during declining solar activity. All parameters are sorted in solar wind speed classes. The radial gradients show a similar behavior for both ion species. In the slow solar wind protons as well as α particles are found to expand adiabatically all the way out to many AUs, while in the fast wind ions evolve non‐adiabatically and are heated by interplanetary sources. The α particle to proton temperature and density ratios are also determined. They do not show any clear radial depend

ISSN:0094-8276    

DOI:10.1029/95GL02595

年代:1995

数据来源: WILEY

摘要:

Characteristic features of the oxygen ion (O+) outflow in the nightside of Mars have been studied. The data set used includes all high telemetry O+energy spectra observations made by the ASPERA particle instrument onboard the Phobos 2 spacecraft. Oxygen outflow within the optical shadow of Mars was detected on all orbits, but no clear structure was found when the ions were organised according to the cross‐flow component of the interplanetary magnetic field (IMF). Oxygen ions in the tail outside the shadow were, in contrast, detected only on a few orbits and were related to fluctuating magnetosheath magnetic and electric fields with non‐Parker spiral IMF orientation. The analysis indicates that O+ions within the optical shadow from a “steady”, ever persisting outflow feature. The high energy O+ions in the tail outside the optical shadow are in contrast possibly a manifestation of the dynamic nature of the Martian tail, although effects associated to an asymmetric tail can not be fully e

ISSN:0094-8276    

DOI:10.1029/95GL02474

年代:1995

数据来源: WILEY

摘要:

A statistical study is made on the reconnection process in the distant tail by using the GEOTAIL observations at x≈ −150 Re and −95 Re in geomagnetically active times with Kp≥3. Occurrence frequencies of various combinations of the field polarity and the convection direction suggest that at least 75% of the reconnection of open field lines occurs inside 150 Re and at least 39% occurs inside 95 Re. At 150 Re the convection of closed field lines constituting the viscous‐like cell is at most 25% of the convection generated by the reconnection of open field lines. The reconnection rate of open field lines varies across the tail and is a few times higher near the tail axis than at t

ISSN:0094-8276    

DOI:10.1029/95GL02420

年代:1995

数据来源: WILEY

摘要:

In response to inconsistencies which have arisen in results from a hydrodynamic model in simulations of high ion temperatures (1–2 eV) observed in low density, outer plasmasphere flux tubes, we postulate a reduced thermal conductivity coefficient in which only particles in the loss cone of the quasi‐collisionless plasma contribute to the thermal conduction. Other particles are assumed to magnetically mirror before they reach the topside ionosphere and therefore not to remove thermal energy from the plasmasphere. This concept is used to formulate a mathematically simple, but physically limiting model for a modified thermal conductivity coefficient. When this modified coefficient is employed in the hydrodynamic model in a case study, the inconsistencies between simulation results and observations are largely resolved. The high simulated ion temperatures are achieved with significantly less heat input, and result in substantially lower ion temperatures in the topside ionosphere. We suggest that this mechanism may be operative under the limited low density, refilling conditions in which high ion temperatures are obser

ISSN:0094-8276    

DOI:10.1029/95GL02408

年代:1995

数据来源: WILEY

摘要:

Measurements of fluctuations in total electron content made with a radio interferometer reveal weak but frequent outbursts of total‐electron‐content disturbances, with trace azimuths roughly westward, with trace speeds up to ∼2 km/s, and with temporal periods in the range 100–500 seconds. Statistical tests of the dataset suggest that these disturbances are due to drift of plasmaspheric irregularities past the radio lines‐of‐sight. The phenomenon is likely to provide a new passive tracer of zonal convection in the inner ma

ISSN:0094-8276    

DOI:10.1029/95GL02550

年代:1995

数据来源: WILEY

摘要:

Instruments on the Auroral Turbulence rocket detected several intervals of weak electromagnetic oscillations at frequencies of 6–13 Hz in a strongly flickering auroral arc. These oscillations have amplitudes of up toδB∼ 3 nT andδE∼ 4 mV/m and have downward field‐aligned Poynting fluxes of up to ∼10−5W/m². Fluctuations in the parallel electron flux at about 9 Hz were observed in association with the strongest of these oscillations. Simultaneous ground‐based optical data show that the arc was flickering at frequencies of 8–15 Hz. The observed frequencies would match the oxygen cyclotron frequency at ∼4500 km altitude. In one wave/particle event the apparent lag of the waves behind the modulated electrons implies a modulation source altitude of 2500–5000 km. We interpret these waves as electromagnetic ion cyclotron waves originating in the auror

ISSN:0094-8276    

DOI:10.1029/95GL02409

年代:1995

数据来源: WILEY

摘要:

The Space Experiments with Particle Accelerators (SEPAC) and the Atmospheric Emission Photometric Imager (AEPI) were flown on the ATLAS‐1 shuttle mission in the spring of 1992. In a series of artificial aurora experiments, SEPAC injected electron beam pulses (6.25 keV, 1.2 A) into the Earth's upper atmosphere while the AEPI camera recorded optical emissions in white light continuum and 4278 Å. The intensity, overall size, and structure of the artificial auroras have been compared to results from a two‐stream code which models collisional and transport properties of natural and artificial electron beams. Using the curvature of the magnetic field to resolve the altitude dependence of observed optical emissions, it is found that the beam reaches 110–130 km altitude and excites emissions at intensities that are consistent with model calculations (1 kR). However, it is also concluded that the near‐field intensity (5 kR) exceeds model estimates by one order of magnitude. It is argued that this unexpected enhancement is caused by emissions generated within the first 10's of kilometers of the Orbiter by suprathermal electron fluxes at levels that are orders of magnitude larger than predicted by the purely collisional model. It is suggested that the enhanced flux is due to wave‐particle interactions heating the ambi

ISSN:0094-8276    

DOI:10.1029/95GL02017

年代:1995

数据来源: WILEY

摘要:

In January 1993 an extensive set of radar and optical data was gathered from various key sites around the world during a coordinated “10 Day Run” designed to investigate the coupled dynamic behavior of the upper atmosphere on a large, medium and small scale. As part of this campaign an all‐sky CCD imaging system was operated at Arecibo Observatory, Puerto Rico, to help quantify the response of the low latitude mesosphere‐thermosphere system to short period (<1 hour) gravity waves. Measurements of the OI(557.7 nm) and near infrared OH nightglow emissions were made in conjunction with photometric and ISR radar soundings and revealed an abundance of small‐scale structure in the 80–100 km range. In this letter we apply two‐dimensional spectral analysis techniques to aid in the interpretation of a complex set of image data that consisted of two intersecting quasi‐monochromatic gravity wave patterns progressing on approximately orthogonal headings. An investigation of the spectral content and temporal evolution of these wave motions at each emission altitu

ISSN:0094-8276    

DOI:10.1029/95GL02491

年代:1995

数据来源: WILEY

摘要:

We present simultaneous in situ measurements of turbulence and temperature in the midlatitude mesosphere obtained as part of the DYANA campaign on March 13, 1990 at Biscarrosse, France (44°N, 1°W). In this study, we have extended the temperature measurements of our rocket borne ionization gauge down to 70 km and directly compared them to the small scale density fluctuations. Between 74 and 81 km we observed a unique, sawtooth shape layer in the temperature profile with a slightly superadiabatic lapse rate. In the same region, strong turbulent density fluctuations were present. We interpret these observations as convective adjustment and associated turbulenc

ISSN:0094-8276    

DOI:10.1029/95GL02351

年代:1995

数据来源: WILEY