摘要:

We have used solar wind electron heat fluxes to determine the magnetic polarities of the interplanetary magnetic fields (IMF) during the ISEE-3 observations in 1978–1982. That period included 14 magnetic clouds (MCs) identified by Zhang and Burlaga. The MCs have been modeled as single magnetic flux ropes, and it is generally assumed that they are magnetically closed structures with each end of the flux rope connected to the Sun. The flux rope model is valid only if the magnetic polarity of each MC does not change during the passage of ISEE-3 through the MC. We test this model with the heat flux data, using the dominant heat flux in bidirectional electron heat fluxes to determine the MC polarities. The polarity changes within at least 2, and possibly 6, of the 14 MCs, meaning that those MCs can not fit the model of a single flux rope. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58658

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We suggest a possible technique for remotely observing the acceleration of solar energetic ions toE>1&hthinsp;MeVat coronal shock fronts. It involves the observation of the wings of line emission from ions accelerated in shocks, which could be done with the UVCS experiment on the SOHO spacecraft. UVCS has two UV channels producing stigmatic spectra from 42 arc min slits that can observe the Ly&agr; and O VI lines, both of which could be broadened with the passage of a shock. In that case, the Ly&agr; line formation results from proton charge exchange and collisional excitation of hydrogen atoms, while the broadened O VI lines are due to directly acceleratedO5+ions. The search criterion for candidate SOHO events consists of UVCS observations of coronal regions flanking or ahead of fast(v>400&hthinsp;km/s)white light CMEs observed with the LASCO coronagraph. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58666

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Interplanetary magnetic field measurements made as NEAR approached Earth in December 1997 have allowed us to compare a magnetic cloud like event seen by the NEAR and WIND spacecraft. The magnetic cloud seen by WIND and NEAR has temporal signatures both in magnitude and direction that indicate a similar geometry and orientation. The magnetic helicity of the cloud structure seen at NEAR is the same as at WIND. The magnitude of the field in the cloud event is consistently lower at NEAR than at WIND as expected for radial convection plus expansion. We model the field of this cloud structure at each spacecraft, obtain fits to the cloud axis as well as rates of expansion, and find that the predicted spacecraft separation distance is consistent with observations. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58822

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Coronal mass ejections are believed to be produced in the corona from closed magnetic regions not previously participating in the solar wind expansion. At 1 AU their interplanetary counterparts (ICMEs) generally have a number of distinct plasma and field signatures that distinguish them from the ambient solar wind. These include heat flux dropouts, bi-directional streaming, enhanced alpha particle events, times of depressed proton temperatures, intervals of distorted or enhanced magnetic field, and times of large magnetic field rotations characteristic of magnetic clouds. The first three of these signatures are phenomena that occur at some point within the ICME, but do not necessarily persist throughout the entire ICME. The large scale magnetic field rotations, distortions and enhancements, and the proton temperature depressions tend to mark more accurately the beginning and end of the ICME proper. We examine herein the reliability with which each of these markers identifies ICMEs utilizing ISEE-3 data from 1978–1980. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58659

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Although interplanetary magnetic clouds are due to coronal mass ejections, not all the ejecta found in the interplanetary medium are clouds. In this paper we use Hoeksema’s potential field model of the solar magnetosphere to investigate the characteristics of the large-scale magnetic structures at the site of the solar events associated with 35 interplanetary magnetic clouds. The position of the related large-scale magnetic structures was determined from the location of the near surface solar explosive events (flares and filament eruptions) associated with each cloud, obtained in a previous study. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58713

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We study the forward transient shocks observed by Ulysses near the ecliptic plane during the interval from October 1990 to May 1992 in its journey to Jupiter. For 22 of the shocks we have sufficient data from IMP to determine whether they passed also near the Earth or not, and we find that only 13 of the 22 shocks were detected by both spacecfrat. In all these 13 cases, both spacecraft were within the same magnetic sector. We also study 46 ejecta detected by Ulysses in terms of their positions relative to magnetic sectors. We find that the ejecta are frequently located near or at the sector boundary and sometimes in a different magnetic sector than the preceding shock. The results obtained from this limited data set lend support to the idea that shocks form in interplanetary space by a sudden increase in the solar wind speed from a coronal hole, and ejecta are only accompanying structures of the whole process. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58714

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

In a study of more than 100 transient events in the solar wind with signatures of bidirectional streaming of suprathermal electrons and ions, helium enrichment, and magnetic cloud configuration, we found that most of them were associated with a near-surface solar explosive event. In this paper we use the position of the near-surface solar activity of this set of interplanetary ejecta as a proxy of the position of the whole solar mass ejection, to compare their positions with the neutral line at the source surface obtained by Hoeksema with a potential field model of the solar magnetosphere. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58715

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Interplanetary transients with particular signatures different from the normal solar wind have been observed behind shocks and also without shocks. In this work we study the relations between four well known transient signatures, namely: magnetic clouds, helium enhancements, and bidirectional electron and ion fluxes. We found that although commonly different signatures appear in a single interplanetary transient event, they are not necessarily simultaneous. We also study their association with near-surface solar explosive events, and found that most of them were associated with an H&agr; flare and/or the eruption of a filament near solar central meridian. An east-west asymmetry in the associated solar events seems to exist for some of the signatures. The presence of a coronal hole near the site of the explosive event was also confirmed in the majority of the cases. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58716

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Magnetic clouds appear in interplanetary space most commonly associated with other transient signatures. In a previous study we found that magnetic clouds are always associated with bidirectional fluxes of ions and electrons and in some cases with shocks and helium enrichments. Another interesting result from our previous study is that in most of the cases magnetic clouds are associated with coronal mass ejections accompanied by near surface solar events such as flares and filament eruptions. In this work we took 71 magnetic clouds observed near Earth and studied possible differences in the general characteristics and morphology of clouds associated with a) shocks and helium enhancements, and b) H&agr; flares and/or filament eruptions. We find that the most common profile and the average value of each parameter depends on the accompanying solar wind signatures and on the solar association. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58717

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The self-similar magnetic cloud model of Osherovich, Farrugia and Burlaga (1,2) is based on the exact class of MHD solutions for a magnetic flux rope with polytropic index &ggr; below unity. The problem in this model is reduced to a second order dynamic equation for the nonlinear oscillator. The corresponding effective potential for the case&ggr;>1has only an oscillating mode and the case for&ggr;<1may have two modes: oscillatory and expansion. This model suggests three classes of magnetic clouds with different evolutionary patterns. For the first class (those which cannot overcome the threshold), the profile of the magnetic cloud is rather flat at 1 AU, and the velocity of expansion is small or even shows signs of contraction. The second class (those which have energy sufficient to overcome the threshold) is well described by a free expanding flux tube. The third class has a potential without a well suggesting expansion for all energies. The non-Maxwellian electron distribution function in a cloud explains the origin of the&ggr;<1thermodynamics (3,4). A few polytropes observed in the same cloud suggest a number of magnetic tubes (4,5). To classify complex clouds, we put forward a multi-tube model based on MHD bound-state solutions (6). This model presents clouds as multiple helices embedded in a cylindrical flux rope. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58718

出版商:AIP    

年代:1999

数据来源: AIP