摘要:

A multi‐spacecraft analysis of the decay phase of 26 SEP events is presented, based upon Helios 1 and 2 and IMP8 data. The Helios spacecraft were magnetically connected to the far side of the Sun for part of their lifetime, and detected SEP events at large longitudinal separation from the location of the associated flares. In this study, 26 SEP events are considered, 19 of which observed by three spacecraft and 7 by two. For each event, the total event duration at 1 electron and 2 proton energies is measured. A plot of event duration versus the longitudinal distance &Dgr;&fgr; between the associated flare location and the footpoint of the magnetic field line through the spacecraft reveals asymmetries in the detection and duration of SEP events. First, SEP events associated with flares far to the east of the spacecraft footpoint are 5 times more likely than events associated with flares far to the west. Second, the event duration shows a tendency to decrease as the location of the associated flare changes from east to west. We show that the first asymmetry is not a result of the trajectory of the spacecraft. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618681

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We present numerical results that show, first, conditions under which parallel scattering reduces the effectiveness of perpendicular scattering, leading to the phenomenon of subdiffusion (“compound diffusion”), and second, that when sufficiently strong three dimensional effects are present, true diffusion is restored, with a suppressed perpendicular diffusion coefficient that depends upon the parallel mean free path. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618682

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We present SOHO/CELIAS/HSTOF data on suprathermal H, He, CNO, and Fe ions in the energy range 0.035–2 MeV/amu associated with the Bastille Day coronal mass ejection event, July 14–16, 2000. We observe a complicated evolution of the spectra in the plasma upstream from the strong interplanetary shock on July 15, in the downstream turbulent compression region, and in the magnetic cloud following the compression region. The spectra of suprathermal H, CNO, and Fe ions from the solar wind source fit a scheme of ordering by their charge‐to‐mass (Q/A) ratio. This scheme suggests that the ions are stochastically accelerated in the turbulence region downstream from the shock and then injected into first‐order Fermi acceleration. The suprathermal He flux consists of solar wind4He2+ions matching the Q/A‐ordering scheme, and an additional component. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618683

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A model for the acceleration and transport of suprathermal ions associated with interplanetary coronal mass ejections (CMEs) is presented. The combined mechanisms of stochastic acceleration in the turbulence near interplanetary shocks, first‐order Fermi acceleration, stationary spatial diffusion in field irregularities of magnetic clouds, and time‐dependent propagation in the upstream solar wind are described. Ions from the bulk solar wind are considered as source populations of suprathermal ions. The results of the model are compared to the spectra of suprathermal ions observed with SOHO/CELIAS/HSTOF during the Bastille Day CME of 14–16 July 2000. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618684

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

To predict the occurrence of major solar wind velocities near the Earth, hourly solar wind speed magnitudes from November 1963 to May 2000 are considered by applying Gumbel’s first distribution. According to the present study a maximum value equal to (1017 ± 50) km/sec is expected to observe during the current solar cycle as a consequence of this result, we infer the possibility to detect intense geomagnetic storms on the Earth. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618685

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Interplanetary coronal mass ejections (ICMEs) are characterized by a number of signatures. In particular, we examine the relationship between Fe charge states and other signatures during ICMEs in solar cycle 23. Though enhanced Fe charge states characterize many ICMEs, average charge states vary from event to event, are more likely to be enhanced in faster or flare‐related ICMEs, and do not appear to depend on whether the ICME is a magnetic cloud. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618686

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We present a study of the elemental composition of a sub‐set of coronal mass ejections, namely events which have been identified of being of the magnetic cloud type (MC). We used plasma density data from the MTOF sensor of the CELIAS instrument of the SOHO mission and plasma ionization data from the SWICS instrument of the ACE mission. So far we have investigated MCs of 1997 and 1998. The study covers the proton and heavy ion elemental abundances. Considerable variations from event to event exist with regard to the density of the individual species with respect to regular “slow” solar wind preceding the MC plasma. However, two general features are observed. First, we observe for the heavy elements (carbon through iron), which can be regarded as tracers in the solar wind plasma, a mass‐dependent enrichment of ions monotonically increasing with mass. The enrichment can be explained by a previously published theoretical model assuming coronal plasma loops on the solar surface being the precursor structure of the MC. Second, when comparing the MC plasma to regular solar wind composition preceding the event, a net depletion of the lighter ions is always observed. Proton and alpha particle abundances have to be regarded separately since they represent the main plasma. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618687

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Three dimensional magnetohydrodynamic numerical simulations of propagating interplanetary flux ropes are presented and compared with “in‐situ” spacecraft measurements. Flux ropes are injected near the Sun with various inclinations. Specific features followed from simulations, as double‐peak magnetic field profiles or a possibility to observe one flux rope two times by the same spacecraft, are searched in observational data. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618688

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The topological properties of the typical current structures in a turbulent magnetohydrodynamic flow can be measured using the cancellations analysis. In two‐dimensional numerical simulations, this reveals current filaments being the most typical current structures. The observations of the topology of photospheric current structures within active regions shows that modifications occur correspondingly with strong flares. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618689

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A212‐DMHD numerical model is used to investigate the dynamic interaction between two flux ropes (clouds) in a homogeneous magnetized plasma. One cloud is set into motion while the other is initially at rest. The moving cloud generates a shock which interacts with the second cloud. Two cases with different characteristic speeds within the second cloud are presented. The shock front is significantly distorted when it propagates faster (slower) in the cloud with larger (smaller) characteristic speed. Correspondingly, the density behind the shock front becomes smaller (larger). Later, the clouds approach each other and by a momentum exchange they come to a common speed. The oppositely directed magnetic fields are pushed together, a driven magnetic reconnection takes a place, and the two flux ropes gradually coalescence into a single flux rope. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618690

出版商:AIP    

年代:1903

数据来源: AIP