摘要:

This paper uses white-light measurements made by the SOHO LASCO coronagraph and HAO Mauna Loa Mk III K-coronameter to illustrate the new view of solar wind structure deduced originally from radio occultation measurements. It is shown that the density profile closest to the Sun at 1.15 Ro, representing the imprint of the Sun, is carried essentially radially into interplanetary space by small-scale raylike structures that permeate the solar corona and which have only been observed by radio occultation measurements. The only exception is the small volume of interplanetary space occupied by the heliospheric plasma sheet that evolves from coronal streamers within a few solar radii of the Sun. The radial preservation of the density profile also implies that a significant fraction of field lines which extend into interplanetary space originate from the quiet Sun, and are indistinguishable in character from those emanating from polar coronal holes. The white-light measurements dispel the long-held belief that the boundaries of polar coronal holes diverge significantly, and further support the view originally proposed in (1) that the fast solar wind originates from the quiet Sun as well as polar coronal holes. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58719

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We have developed a 2D semi-empirical MHD model (1) of the solar corona and the solar wind. The model uses empirically derived electron density profiles from the white light coronagraph data measured during the Whole Sun Month observing campaign of SOHO and an empirically derived model of the magnetic field which is fit to observed coronal hole boundary which come from white light and EUV observations. The electron density model is extended into interplanetary space by using electron densities derived from the Ulysses instrument. The model also requires an estimate of the solar wind velocity as a function of heliographic latitude and the radial component of the magnetic field at 1 AU, both of which can be provided by the Ulysses spacecraft. The model makes estimates as a function of radial distance and latitude of various fluid parameters of the plasma such as flow velocityV&vec;,temperatureTeff,and heat fluxqeffwhich are derived from the equations of conservations of mass, momentum and energy, respectively in the rotating frame of the Sun. The term effective indicates possible wave contributions. Both the observations as well as the model results of the various plasma properties show a clear separation at the boundary of the fast and slow solar wind. This boundary is directly established by the global magnetic field topology inferred from observations. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58786

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

By measuring the frequency drift rate of type III bursts observed continously from 13.8 MHz to a few kHz, we have derived the electron density distribution in the ecliptic plane, from the corona to 1 AU. This method is a powerful probe to explore the region between1.8&hthinsp;Roto 1 AU, most of which is not observed by coronographs. The observations were made by the radio experiment WAVES aboard the spacecraft Wind. We have selected type III bursts whose trajectories intersect the spacecraft, as determined by the presence of burst-associated Langmuir waves, or by energetic electrons observed by the 3-D Plasma experiment. For these bursts we are able to determine the mode of emission, the electron density at 1 AU, the distance of emission regions along the spiral, and the time spent by the beams as they proceed from the low corona to 1 AU. An average density model is derived, valid for solar minimum:ne=3.3×105r−2+4.1×106r−4+8.0×107r−6&hthinsp;cm−3,withrin units ofRo.We show how, for a given day, the density distribution departs from the average model. As an application, we derive the speed of the shock of 7 April 1997 which produced a type II burst from 75 to 0.9 MHz (1.2 to13&hthinsp;Ro). For this event, a flare, a fast CME and the initiation of the type II burst occurred simultaneously to with in a few minutes. The derived speed of the type II shock in the solar wind leads to the arrival of the interplanetary shock at the Earth on 10 April at 1300 UT, as was observed. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58787

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

A summary of the new model of the heliospheric magnetic field and its observational implications is presented. We first introduce a global model for the steady-state configuration in the low corona and discuss solar and heliospheric implications of the resulting field configuration. Finally, we compare the effects of this model with random transport of field-lines due to reconnection on the solar surface and to the dynamic turbulent transport of magnetic field-lines. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58737

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Recent progress regarding multiple spacecraft crossings of the heliospheric current sheet (HCS) is reviewed and placed in the context of streamer belt and heliospheric plasma sheet structure. Historically, multiple crossings have been attributed to waves on the HCS surface. Mounting evidence, however, argues against that view. Most notably, recent application of a heat flux polarity test to 47 cases of multiple crossings in the ISEE 3 data set rules out the possibility that they were caused by the HCS folded back on itself. More than half of these cases contained counterstreaming electrons indicating association with coronal mass ejections (CMEs), and the remaining cases lacked the heat flux pattern required for a folded current sheet. An alternative explanation of the non-CME associated multiple crossings in terms of multiple current sheets is consistent with the data but in a turbulent rather than laminar form. The data suggest passage through a network of tubular current sheets constituting the walls of tangled flux tubes. Multiple HCS crossings are associated with multiple plasma sheet crossings and occur on a hierarchy of scale sizes. These may reflect the hierarchy of scale sizes of transient outflow observed in the streamer belt near the Sun. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58738

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Current modeling of long-term (11-year) cosmic ray modulation incorporates as a major component the so-called “Global Merged Interaction Regions” (GMIRs). GMIRs are assumed to be formed beyond about 10 AU by the merging of systems of coronal mass ejections (CMEs) and existing interaction regions. Merged interaction regions are identified from outer heliospheric magnetic field observations as complex structures and enhancements above the average field strength. We demonstrate that the ∼1 year cosmic ray modulation events supposedly caused by GMIRs are already apparent at 1 AU, with the effects of individual major CMEs superimposed. Thus, GMIRs are unlikely to be the prime cause of long-term cosmic ray modulation. We show that the cosmic ray intensity is anti-correlated with the interplanetary magnetic field strength (IMF). The IMF shows an overall solar-cycle variation of about a factor of 2 together with episodic increases with durations of about a year which do not form in the interplanetary medium but are related to global variations of the solar photospheric magnetic field. We point out, once again, that cosmic rays are important probes of the structure of the interplanetary medium. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58653

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

From Ulysses observations of magnetic field and plasma properties during its rapid pole-to-pole scan, we determine the causes of variations in the magnitude of the radial component of the heliospheric magnetic field (HMF). We find that the ambient radial HMF in the slow solar wind is a combination of the ambient radial HMF components of the two hemispheres with opposite polarities. It suggests that the source region of the slow solar wind has the same magnetic topology as the source region of the fast solar wind, i.e., both are open field regions. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58739

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

This article describes the hydromagnetic relationships among Coronal Mass Ejections, flares and prominences to put these phenomena in the context of the solar corona evolving in response to the solar dynamo. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58788

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We present observations of slowly evolving, balloon-type solar mass ejections observed by the LASCO coronagraphs aboard SOHO. These mass ejections are typically observed to rise gradually in the solar corona for several hours (>20 hours) as large loops or balloons crossing the entire field of view of the coronagraphs. Usually, their angular extent does not change much. Analysis of several such cases of balloon-type mass ejections show that they rise with very slow speeds (less than 50 km s−1) up to a distance of2&hthinsp;R⊙and then are accelerated to higher speeds until5&hthinsp;R⊙.From a distance of about20&hthinsp;R⊙,the mass ejecta attain almost a constant speed ranging between 300 and 500 km s−1. The speed profiles obtained for individual mass ejections indicate that they trace out the slow solar wind and, thus, provide an insight into the initiation and the propagation of the CMEs into the solar wind. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58789

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

This paper provides a brief overview on the magnetic field structure and topology within coronal mass ejections (CMEs) in the solar wind. The overview starts summarizing the magnetic field characteristics within CMEs (magnetic clouds) which exhibit large-scale internal magnetic field rotations indicative of helical magnetic flux ropes and those of non flux rope CMEs lacking smooth internal field rotations. The overview continues with a presentation of Ulysses observations showing evidence for mixed magnetic topologies of open and closed field lines within some CMEs followed by a discussion of the magnetic field structure of CMEs near the Sun in relationship with the observed field properties of CMEs in the solar wind. Finally, the to date main open questions concerning the magnetic origin, evolution and fate of CMEs are addressed. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58740

出版商:AIP    

年代:1999

数据来源: AIP