摘要:

Data recorded by the magnetometers on the German (IRM) and British (UKS) spacecraft of the Active Magnetospheric Particle Tracer Explorers (AMPTE) spacecraft mission are described during the immediate period following the two releases of lithium from the IRM during September. Ions created in the first seconds of the release form a coherent obstacle to solar wind flow. A cavity from which the interplanetary magnetic field is excluded is detected. Outside the cavity the field is compressed, and subsequently the cavity is convected downstream. We compare what is observed with other relevant natural interactions but also emphasize the unique features of this experiment.

ISSN:0148-0227    

DOI:10.1029/JA091iA02p01261

年代:1986

数据来源: WILEY

摘要:

This paper investigates the lithium releases in the solar wind as they appear in the measurements of ions and electrons above 20 eV/q and 15 eV, respectively, made with the Max‐Planck‐Institut für extraterrestrische Physik/University of California, Berkeley, fast three‐dimensional plasma instrument on AMPTE/IRM. The dominant effects are the pick up of the newly created Li ions by the solar wind electric field and the heating of electrons. When first observed, the beam of Li ions is substantially broadened, probably as a result of its interaction with the cross‐streaming solar wind. Later on, when the Li density has decreased, the Li beam becomes narrower than can be resolved by the instrument. The observed increase of beam energies with time to more than ∼1 keV can be directly attributed to the expansion of the lithium atoms with a maximum speed of ∼3.8 km/s. Throughout the observations the Li ions move nearly along the electric field direction. This is a result of their large gyroradius. Shortly after the release, while the spacecraft is still within the magnetic cavity, hot (E>70 eV) electrons are observed. Their density and temperature is further enhanced when entering the magnetic field compression region ahead of the cavity, consistent with adiabatic heating. There is no evidence in our data of a shock in the upstream region, nor of reflected sol

ISSN:0148-0227    

DOI:10.1029/JA091iA02p01271

年代:1986

数据来源: WILEY

摘要:

The two September 1984 solar wind lithium releases produced a rich variety of plasma waves which have been measured in situ by the plasma wave instrumentation on board the Active Magnetospheric Particle Tracer Explorers (AMPTE) IRM and UKS spacecraft. Reflection of the natural galactic and terrestrial electromagnetic radiation from the dense Li plasma caused a cutoff in the high‐frequency electric field intensities from which the temporal and spatial variation of the plasma density can be determined. Inside the diamagnetic cavity the electron plasma frequency and also temporarily the Li plasma frequency have been excited. The emission at the electron plasma frequency is near the thermal fluctuation level. In addition, weak low‐frequency ion acoustic waves were observed. The boundary between the diamagnetic cavity and the external magnetic field was found to be surprisingly stable and contained extremely low levels of wave activity. In the transition region from the diamagnetic cavity to the solar wind, high wave activity at the medium and very low frequencies propagating mainly in the ion acoustic and electrostatic cyclotron harmonic modes was encountered. No wave magnetic fields were detected in this region. The upstream edge of the transition region was characterized by a steep decay in magnetic field strength and density and by a sudden increase in the quasi‐static electric field. At this time the ELF/MF rms wave amplitude explosively increased to a value of 50 mV/m and remained at an enhanced level for more than 1 min. The spectrum of this wave activity is similar to the electrostatic noise observed in collisionless shocks. Data from UKS indicate that during the releases, UKS was in the magnetic transition zone. The wave activity at UKS was distinctly different from that encountered by IRM. The intense emission at the electrostatic shocklike transition was weaker than that on IRM and for the second release appeared at a different time. This can be related to the different positions of the two spacecraft with respect to the interaction regions. Despite the high wave intensities the estimated wave energy densities are, however, too low by orders of magnitude to drive significant magnetic field diffusion during the in situ observation times. Some differences in the wave excitations for the two releases can be traced back to the different solar wind condi

ISSN:0148-0227    

DOI:10.1029/JA091iA02p01283

年代:1986

数据来源: WILEY

摘要:

During the Active Magnetospheric Particle Tracer Explorers (AMPTE) solar wind lithium release on September 11, 1984, and again on September 20, 1984, an intense burst of electrostatic noise was observed near the upstream edge of the ion cloud. Comparisons with measurements by the IMP 6 and ISEE 1 spacecraft show that the spectrum and overall features of this noise are very similar to electrostatic noise observed at the earth's bow shock. A stability analysis using realistic parameters shows that the electrostatic noise can be accounted for by an ion beam‐plasma instability caused by the solar wind proton beam streaming through the nearly stationary lithium cloud. The growth rate of this instability is largest when the ion density and solar wind proton density are similar, which explains why the noise only occurs near the outer edge of the ion cloud. The similarity to the noise in the earth's bow shock suggests that a shock may exist in the solar wind plasma flow upstream of the ion cloud. If the noise is associated with a shock, then it must be an electrostatic shock, since the ion cyclotron radii are too small for the existence of a MHD shock. Since the electrostatic instability occurs at phase velocities near the lithium thermal velocity, the electrostatic turbulence may play a role in heating the lithium ions and transferring momentum from the solar wind to the ion cloud. The noise may also play a role in the pitch angle scattering and diffusion of energetic electrons observed in the vicinity of the ion cloud. Because of the similarity to the solar wind interaction with the gaseous envelope of a comet, it is expected that similar types of wave‐particle effects may occur upstream of com

ISSN:0148-0227    

DOI:10.1029/JA091iA02p01301

年代:1986

数据来源: WILEY

摘要:

The two Active Magnetospheric Particle Tracer Explorers (AMPTE) lithium releases outside the bow shock were made in quite different conditions in the solar wind. The first took place in a high speed stream in the presence of a diffuse distribution of upstream ions which disturbed the solar wind. Lithium ions were only detected for 15 seconds. During the second release the solar wind flow was much smoother and slower. The lithium ions were observed for 4 minutes. In that time the energy of the detected ions increased from 10 eV up to almost 3 keV. This is consistent with a shell‐like expansion of the neutral lithium cloud and acceleration of the ions in the convection electric field. The solar wind slowed down and was deflected as it passed through the ion clou

ISSN:0148-0227    

DOI:10.1029/JA091iA02p01311

年代:1986

数据来源: WILEY

摘要:

Following releases of lithium ions into the solar wind by the Active Magnetospheric Particle Tracer Explorers (AMPTE)‐IRM spacecraft on September 11 and 20, 1984, electron intensities measured at the AMPTE/UKS spacecraft, some 33 km away from the IRM, increased significantly for tens of seconds. The causes of the increases are considered and found to be the result of energization of solar wind electrons. The degree of energy dependence of the energization is established, and possible causative processes are considered. No positive indications of adiabatic compression or acceleration through a potential difference are found. There is, however, evidence for a resonant wave‐particle interact

ISSN:0148-0227    

DOI:10.1029/JA091iA02p01320

年代:1986

数据来源: WILEY

摘要:

Newly created 5‐ to 20‐keV lithium ions were observed for limited time periods following the first Active Magnetospheric Particle Tracer Explorers (AMPTE) lithium release in the solar wind on September 11, 1984. The detection of these so‐called “pick‐up” ions by the time‐of‐flight spectrometer SULEICA (suprathermal energy ionic charge analyzer) on the AMPTE/IRM satellite depends critically on the orientation of the interplanetary magnetic field with respect to the directions of the solar wind and the spin axis of the IRM spacecraft, which was favorable only during the short time when these ions were seen. Our observations are compatible with a shell‐like expansion of the Li cloud with velocities of about 2.5 km/s. The signatures by which the artificial pick‐up ions are identified can also be used to detect and investigate n

ISSN:0148-0227    

DOI:10.1029/JA091iA02p01325

年代:1986

数据来源: WILEY

摘要:

The early time interaction of an artificially injected lithium cloud with the solar wind is simulated with a one‐dimensional hybrid code. Simulation results indicate that the lithium cloud presents an obstacle to the solar wind flow, forming a shock‐like interaction region. Several notable features are found: (1) The magnetic field is enhanced up to a factor of about 6, followed by a magnetic cavity downstream. (2) Solar wind ions are slowed down inside the lithium cloud, with substantial upstream reflection. (3) Most of the lithium ions gradually pick up the velocity of the solar wind and move downstream. (4) Intense and short‐wavelength electric fields exist ahead of the interaction region. (5) Strong electron heating occurs within the lithium cloud. (6) The convection electric field in the solar wind is modulated in the interaction region. The simulation results are in remarkable agreement with in situ spacecraft measurements made during lithium releases in the solar wind by the AMPTE (Active Magnetospheric Particle Tracer Explorers) Pr

ISSN:0148-0227    

DOI:10.1029/JA091iA02p01333

年代:1986

数据来源: WILEY

摘要:

A release of approximately 3.3×1025lithium atoms was made on September 11 and again on September 20, 1984, by the Active Magnetospheric Particle Tracer Explorers (AMPTE) Ion Release Module (IRM) spacecraft at a geocentric distance of ≈ 18.8Rein the subsolar direction, creating an ion cloud approximately 4Rein diameter after one hour. Detailed modeling of ion propagation to the bow shock and transport through the magnetosheath shows that ≳20% (September 11) and ≳50% (September 20) of the ions mapped to a 36‐Re² area around the stagnation point on the magnetopause. The AMPTE Charge Composition Explorer (CCE) satellite, located inside the magnetosphere with an apogee of 8.78Reand inclination of 4.8°, at a local time of about 1300 MLT, was instrumented to detect lithium ions over the energy range from a few eV to ≳6 MeV. Detailed analysis of the data for the several hours following the lithium releases shows that no measurable lithium ion fluxes reached the location of the CCE; upper limits to the lithium flux atL≳ 8 are about 50 to 70 (cm2‐sec‐sr)−1in the range 25–300 keV/e(Li/H ≳ 2×10−5), and about 0.1 to 1 (cm²‐sec‐sr)−1in the range 45–100 keV/nucleon (Li/H ≈ 1×10−6). The implications of these results are discussed in the context of current theoretical models of plasma entry in

ISSN:0148-0227    

DOI:10.1029/JA091iA02p01339

年代:1986

数据来源: WILEY

摘要:

When the counting rates of neutron monitors at two different cutoff rigidities are plotted against each other, steplike changes in the rigidity dependence of the modulation are observed, leading to the well‐known hysteresis effect. These steplike changes are generally related to the modulation effects of solar flare‐induced shocks propagating through the heliosphere. Shock acceleration as a mechanism for the steplike changes has however not yet been considered explicitly. Therefore, in this paper it is shown that the acceleration effects of multiple shocks in the outer heliosphere may indeed explain these st

ISSN:0148-0227    

DOI:10.1029/JA091iA02p01355

年代:1986

数据来源: WILEY