摘要:

We discuss the solar and interplanetary characteristics of six interplanetary shock and energetic particle events associated with the eruptions of solar filaments lying outside active regions. The events are characterized by the familiar double‐ribbon Hα brightenings observed with large flares, but only very weak soft X ray and microwave bursts. Both impulsive phases and metric type II bursts are absent in all six events. The energetic particles observed near the earth appear to be accelerated predominantly in the interplanetary shocks. The interplanetary shock speeds are lower and the longitudinal extents considerably less than those of flare‐associated shocks. Three of the events were associated with unusual enhancements of singly ionized helium in the solar wind following the shocks. These enhancements appear to be direct detections of the cool filament material expelled from the corona. We suggest that these events are part of a spectrum of solar eruptive events which include both weaker events and large flares. Despite their unimpressive and unreported solar signatures, the quiescent filament eruptions can result in substantial space and geophysical disturba

ISSN:0148-0227    

DOI:10.1029/JA091iA12p13321

年代:1986

数据来源: WILEY

摘要:

During September 1979, Helios B (HB) and Voyager 1 (V1) were near 0.85 AU and 6.2 AU, respectively, and they were radially aligned with respect to the sun within 20°. A slow transient stream, two corotating streams, and two unusually fast transient streams passed HB during a 17‐day interval in that order. (A stream is defined here as a flow in which the speed is always greater than 475 km/s.) As the streams moved outward from HB to V1, they coalesced to form a single large “compound stream” which moved past V1 in 20 days. The compound stream was produced by motion of fast plasma away from slower plasma behind and by the interaction of the fast streams with slower streams ahead. The maximum speed observed was 1270 km/s at HB and 860 km/s at V1. Closely associated with this compound stream was one of the largest solar energetic particle events (protons 0.4–69 MeV) observed beyond 5 AU. The maximum intensity was in the region of increasing speed. The intensity‐time profile of the solar energetic particles was closely related to the speed profile. There is evidence of channeling and trapping of particles in a region following the highest speeds, where the magnetic field was strong and the magnetic field lines were nearly radial. The high‐energy protons (>150 MeV) and MeV electrons are believed to be accelerated in solar flare events. Interplanetary acceleration appears to play a major role in the low‐energy particle population. The galactic cosmic ray intensity remained low throughout the passage of the compound stream, recovering slowly as the speed decreased. The long “recovery time” is thus related to the large

ISSN:0148-0227    

DOI:10.1029/JA091iA12p13331

年代:1986

数据来源: WILEY

摘要:

In September 1979 an unusual large‐scale interplanetary compound stream was observed in data from the plasma and magnetic fields experiments on Voyager 1 at a heliocentric distance of 6.2 AU. Two interaction regions were observed by Voyager 1, each lasting more than 4 days, in which the total pressure was nearly 100 times the ambient pressure. Speeds of greater than 450 km/s were observed for more than 27 days. A strong forward shock FDwith a shock speed of 960 km/s and a density ratio of 3.85 was present at the front of the second interaction region, and two reverse shocks, R1 and R2, were at the end of the first interaction region. A major restructuring of the flow took place over the distance of 3.3 AU between Voyager 1 and Pioneer 11, which was nearly radially aligned with Voyager 1. During the restructuring the two interaction regions observed at 6.2 AU coalesced to form a new single structure (a “merged interaction region”) at 9.5 AU. This paper presents a simulation study of the evolution and interaction of solar wind structures to explain the observed restructuring process. The computer simulation is based on an unsteady, one‐dimensional, one‐fluid, MHD model and uses the plasma and magnetic field data from Voyager 1 at 6.2 AU as the input function. The model shows that the forward shock FDpassed through the reverse shocks R1 and R2 and into the first interaction region, becoming weaker in each of these interactions. The reverse shocks coalesced to form a stronger reverse shock R; thus the shock signature changed from R1‐R2‐FDto FD‐R between 6.2 and 9.5 AU. The major stream structures at 9.5 AU predicted by the simulation model agree well with those directly observed

ISSN:0148-0227    

DOI:10.1029/JA091iA12p13341

年代:1986

数据来源: WILEY

摘要:

We describe a test particle simulation designed to study energetic charged particle acceleration at oblique fast‐mode shocks when magnetic fluctuations exist upstream and downstream of the shock. The technique consists of integrating along exact particle orbits in a system where the angle θ1between the shock normal and mean upstream magnetic field, the level of magnetic fluctuations, and the energy of injected particles can assume a range of values. This allows us to study time‐dependent shock acceleration under conditions not amenable to analytical techniques. To illustrate the capability of the numerical model, we consider proton acceleration under conditions appropriate for interplanetary shocks near 1 AU, including large‐amplitude transverse magnetic fluctuations derived from power spectra of both ambient and shock‐associated MHD waves. With all other parameters held fixed, protons injected at θ1= 0° and θ1= 60° shocks are accelerated from 10 keV to ∼100 keV and ∼ 1 MeV, respectively, within 300 gyroperiods by a combination of the shock drift and first‐order Fermi processes. The energy spectrum downstream of the 60° shock can be fit with two power laws, with spectral exponent γ = 1.7 from 10 keV to ∼80 keV and γ = 2.6 from ∼ 80 keV to 800 keV. Results are also presented for the situation where the variance and upstream extent of the shock‐associated waves at the 60° shock are reduced relative to the

ISSN:0148-0227    

DOI:10.1029/JA091iA12p13349

年代:1986

数据来源: WILEY

摘要:

Analyses of Alfvenic fluctuations in the solar wind contain a systematic effect in which outward propagation is favored. The effect is generally small at and beyond 1 AU in a Mach 10 flow but can become important where the Mach number is lower, e.g. inside 1 AU. If the propagation speeds of the inward and outward propagating Alfvenic fluctuations are properly included, this systematic effect can be removed. A technique for doing this is illustrated using both artificial and spacecraft data. The results suggest that time intervals originally thought to be outward propagating sometimes contain wave number bands in the cross helicity spectrum of inward propagating Alfvenic fluctuations.

ISSN:0148-0227    

DOI:10.1029/JA091iA12p13357

年代:1986

数据来源: WILEY

摘要:

Twelve proton velocity distribution functions as measured for different solar wind speeds by the plasma analyzer at the Helios spacecraft are modelled analytically by a superposition of two bi‐Maxwellians. The stability of these distributions is investigated by solving the linear dispersion equation for parallel propagation of both left‐ and right‐hand polarized modes. Due to the temperature anisotropy of the main proton component the presence of the resonant left‐hand ion cyclotron instability is found to be typical for high‐speed streams and is independent of an ion beam. The results indicate that the ratio of the beam density to total particle density and the beam drift velocity are generally close to the threshold values necessary to drive a highly unstable nonresonant right‐hand mode. This instability is found for one proton distribution and is a consequence of the beam particles. It is concluded that both the ion cyclotron instability and the ion beam instability act as a regulating mechanism on the shape of solar wind double humped proton distributio

ISSN:0148-0227    

DOI:10.1029/JA091iA12p13366

年代:1986

数据来源: WILEY

摘要:

The plasma dynamics associated with both the single and multiple X line reconnection processes is studied based on an MHD simulation. It is found that the plasma dynamics in the single X line reconnection is generally consistent with the reconnection models by Petschek and Sonnerup. However, the outflow plasma speed is considerably smaller than the upstream Alfvén speed predicted by the theoretical models. In the case of multiple X line reconnection, repeated formation and convection of magnetic islands are observed with a recurrence time τ ≃ 10tA/Ro, where tAis the Alfvén transit time, and Ro= V1/VAis the imposed driving rate. The magnetic reconnection process is found to be impulsive and intermittent. An exponential growth of the reconnection rate is observed during the impulsive phase. The simulation results are generally consistent with satellite observations of flux transfer events (FTE's). The BNsignature associated with the FTE's is observed in our simulation. Magnetic flux tubes with a cross section of ∼1 RE² are found to occur repeatedly every 5–15 min in our s

ISSN:0148-0227    

DOI:10.1029/JA091iA12p13373

年代:1986

数据来源: WILEY

摘要:

The multiple X line reconnection process, which was proposed by Lee and Fu to explain the flux transfer events observed at the dayside magnetopause, is studied by computer simulations based on a two‐dimensional magnetostatic particle code. A driven boundary condition is applied at the two sides of the simulation domain with an incoming plasma flow while a free boundary condition is used at the other two sides with an outflow. Repeated formation and convection of magnetic islands are observed in the simulation. Magnetic islands with various sizes are observed. Superthermal ions of energy 5–50 keV, with an energy spectrum f(E)∼E−1.9, are generated during the multiple X line reconnection process. It is found that the power spectrum of the normal magnetic field is given by a power law PB∼ k−0.6, where k is the wave number. The convection speed of magnetic islands may exceed the Alfvén speed. The recurrence time of magnetic islands is found to be τ ≃ 100/ΩRo, where Ω is the ion gyrofrequency, Ro= V1/VA, V1is the imposed inflow speed, and VAis the Alfvén speed. Our results are consistent with satellite observations of fl

ISSN:0148-0227    

DOI:10.1029/JA091iA12p13384

年代:1986

数据来源: WILEY

摘要:

Empirical studies indicate that the rate of energy transfer to the magnetosphere increases as solar wind coupling parameters increase, up to a certain limit, and then the rate remains constant. The split separator line merging model undergoes the same behavior. When the model interplanetary magnetic field (IMF) magnitude exceeds a critical value, the field configuration in the Chapman‐Ferraro current plane ceases to expose closed field lines to the solar wind. The critical value depends upon IMF orientation, stagnation pressure, and earth's dipole tilt angle. The absence of exposed closed field lines prevents closed‐to‐open flux transfer and, consequently, energy transfer. Further, the limit on energy transfer governed by the model dipole tilt angle affords the first explanation of both the semiannual and UT variations of geomagnetic activity completely in terms of me

ISSN:0148-0227    

DOI:10.1029/JA091iA12p13393

年代:1986

数据来源: WILEY

摘要:

A classical, storm time Pc 5 event (T∼ 160 s) was recorded by the satellite pair ISEE 1, 2 during an inbound, nearly equatorial pass in the dusk sector on August 21–22, 1978. Irregular and quasi‐periodic pulsations composed of several harmonics (f∼ 2–10 × 10−3Hz) were recorded from just inside the magnetopause at 11REto a distance of ∼8RE, where the pulsations became nearly sinusoidal, and disappeared at ∼7REjust outside the plasmapause. Comparison of signals from the two spacecraft throughout the pass shows remarkable similarity of waveform at the second spacecraft following a few hundred to a thousand kilometers (∼300 s) behind the first. This duplication of waveforms having wave periods commensurate with the spacecraft separation time suggests that the two satellites were sampling slightly different phases of the same wave cycle. The more distant, irregular pulsations were encountered by the two spacecraft with essentially no consistent delay between them, while the innermost, regular waves were always encountered first by the leading spacecraft. Cycle‐by‐cycle hodograms show nearly linear or highly elliptical polarization in the meridian plane everywhere on the inbound orbit, dominated by compressional waves. During the last few cycles the ellipses broadened and reversed phase at both satellites, just before the oscillations terminated, while the azimuthal amplitude went to zero at one satellite but not at the other. The Pc 5 pulsations occurred during an interval of strongly southward interplanetary magnetic field and substorm activity and were accompanied by Pc 1 w

ISSN:0148-0227    

DOI:10.1029/JA091iA12p13398

年代:1986

数据来源: WILEY