摘要:

We report observations of the neutral component of the solar wind from the Low Energy Neutral Atom (LENA) imager on the NASA IMAGE spacecraft from year 2001. There is a pronounced annual modulation of the neutral solar wind, and the flux outside of the upstream region is used to place an upper limit on the dust geometric cross section in the sunward direction at 1 AU of &Ggr;1AU< 6×10−19cm−1. This value agrees with inferences made from the zodiacal light. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618711

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A method of potentials has been used in the past for the calculation of the force acting on isolated magnetic bodies in solar corona and inner heliosphere, where large gradients of magnetic pressure exist. Since recent observations showed that coronal mass ejections (CME) can leave the Sun more frequently than was expected before 1995, it is clear that interactions between CMEs can play important role in the formation of geo‐effective structures near the Earth’s orbit. We present here an evaluation of two interacting CMEs and the field distribution around them, using potential solution in bi‐cylindrical coordinates. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618712

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

After about 40 years of solar wind and heliospheric space research questions about the structure and the origin of the solar wind still await an answer. We still don’t understand how the corona is heated and how the solar wind is accelerated, what are the sources for the fast and slow wind. Recent findings seem to indicate that the magnetic patterns below the sun’s surface and the coronal structure are intimately connected, but quantitative connections are difficult to make. Modeling shows that the strength of the solar wind and coronal mass ejections controls the spatial and temporal response of the heliospheric boundary, while the physical state of the surrounding interstellar medium sets the boundary conditions. With a fleet of solar and heliospheric spacecraft throughout the heliosphere we have a unique situation that enables us to make substantial progress, and “Living with a Star” will add a comprehensive 3D view of the inner heliosphere. However, the fundamental questions cannot be solved without in‐situ sampling to within a few solar radii, and the heliospheric boundary will not be fully understood without crossing it. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618713

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The first part of this paper reviews some issues representing major computational challenges for global MHD models of the space environment. These issues include mathematical formulation and discretization of the governing equations that ensure the proper jump conditions and propagation speeds, regions of relativistic Alfve´n speed, and controlling the divergence of the magnetic field. The second part of the paper concentrates on modern solution methods that have been developed by the aerodynamics, applied mathematics and DoE communities. Such methods have recently begun to be implemented in space‐physics codes, which solve the governing equations for a compressible magnetized plasma. These techniques include high‐resolution upwind schemes, block‐based solution‐adaptive grids and domain decomposition for parallelization. We describe the space physics MHD code developed at the University of Michigan, based on the developments listed above. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618714

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

X‐rays should be generated throughout the heliosphere as a consequence of charge transfer collisions between heavy solar wind ions and interstellar neutrals. The high charge state solar wind ions resulting from these collisions are left in highly excited states and emit extreme ultraviolet or soft X‐ray photons. X‐rays should also be generated because of charge transfer collisions with neutral hydrogen in the Earth’s geocorona. Originally a simple model was developed in which both the solar wind and the interstellar neutrals were assumed to be spherically symmetric and time independent. In our updated results, the hot model of Fahr [1] was used to model spatial variations of interstellar helium and hydrogen. At the same time a simple model was created to simulate X‐ray radiation due to the Earth’s geocorona. With the updated information, time independent maps of the heliospheric X‐ray emission across the sky were created. Measured time histories of the solar wind proton flux were used in this updated model and the results were compared with “long term enhancements” in the soft X‐ray background measured by the Ro¨entgen satellite (ROSAT) for the same time period. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618715

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The NASA Solar Probe mission to the inner frontier of the heliosphere is a part of the Sun‐Earth Connection theme within the Office of Space Science. A NASA‐appointed Science Definition Team has defined a Solar Probe mission and its scientific objectives. These include making measurements to understand the processes that heat the solar corona and produce the solar wind, subjects of continuing scientific debate. The Solar Probe mission will accomplish these objectives with a combination ofin situmeasurements designed to characterize the local heating and acceleration of plasma near the Sun and high resolution images to detect small‐scale, transient magnetic structures at and around the Sun. In order to sample the solar corona acceleration region, Solar Probe will fly to four solar radii from the center of the Sun in an orbit inclined 90° to the plane of the ecliptic. Engineering solutions to design a probe that can withstand the near‐Sun environment have been proposed for several decades. Current status of the Solar Probe concept is provided in this paper. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618716

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Solar Orbiter is proposed as a space mission dedicated to study the solar surface, the corona and the solar wind by means of remote sensing and in‐situ measurements, respectively. At 0.21 AU, closest approach to the Sun, the full 3‐D particle velocity distribution should be sampled as fast as a few tens of msec in order to study the growth phase of the instabilities. This implies some restrictions on the maximum phase space resolution given the limited allowed bit‐rate for data transmission. In this paper we evaluate consequences of this limitation for solar wind distributions with different parameters. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618717

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We describe the concept of a proposed mission, called Multi‐Angle Solar Sources Explorer (MASSE´), that would observe the Sun and the inner Heliosphere from an orbit at 0.72 AU over all solar longitudes. It would, in coordination with observations from Earth’s side, investigate the sources of solar activity from their origin deep within the Sun, their emergence onto the photosphere, and their ejection into the Heliosphere. It carries a Doppler‐magnetic imager, and in situ energetic particle, solar wind, and magnetic field detectors. Three‐dimensional views of the convection zone, where solar activity originates, are reconstructed by correlating MASSE´ and earth‐side Doppler signals from acoustic wave packets traversing deep solar layers. Magnetic images reveal the evolution of active regions over their life‐time and allow the study of emerging fields from deep layers. Particle, plasma, and magnetic field data provide information on the sites and mechanisms of acceleration of hazardous high‐energy particles produced by coronal mass ejections. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618718

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

From observations and theory we know that the unshocked solar wind extends at least 80 AU from the Sun but likely no more than ∼100 AU in the region from which the local interstellar wind blows. The much larger region of the shocked solar wind and heliosheath extend out to at least several hundred AU, and fast neutrals from charge‐exchanged supersonic solar wind protons disturb the very local interstellar medium to ∼500 AU or more. Thus to really understand the interaction of the solar wind with the local external medium, a properly‐instrumented, in situ probe to this region of space is required. For more than 20 years, an “Interstellar Precursor Mission” has been discussed as a high priority for multiple scientific objectives. The chief difficulty with actually carrying out such a mission is the need for reaching significant penetration into the interstellar medium (∼1000 Astronomical Units (AU)) within the working lifetime of the initiators (<50 years). We have revisited an old idea for implementing such a mission. The probe and its perihelion carrier are launched initially to Jupiter as a combined package and then fall to the Sun where a large propulsive &squarelg;V maneuver propels the package on a high‐energy, ballistic escape trajectory from the solar system. Outbound in deep space, the two separate, and the probe takes data with its onboard instruments and autonomously downlinks the data to Earth at regular intervals. The implementation requires a low‐mass, highly‐integrated spacecraft to make use of available expendable launch vehicles. We provide a first‐order cut at many of the engineering realities associated with such a mission. These separate into (1) the systems constraints imposed on the perihelion package by the combination of the propulsion system, carrying the needed propellant into perihelion, and the associated thermal and mechanical constraints, and (2) the requirements of power, autonomous operations, and data downlink from the probe itself. We find that many of the requirements for a low‐mass probe that operates autonomously for this mission are common for either this propulsion concept or more advanced low‐thrust concepts, e.g., solar sails and ion propulsion. We describe an implementation that could make such a mission into reality in the next 10 to 20 years. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618719

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Interstellar Pathfinder (ISP), our first step into the interstellar medium, is a scientific investigation to study the outer boundary of our heliosphere and the interstellar matter that flows into it. A wind of interstellar neutral gas penetrates to within several astronomical units (AU) of the Sun, giving us a direct sample of present‐day galactic matter. ISP is a mission to this inner edge of the interstellar medium. Using highly sensitive instrumentation, ISP will determine the composition of our local interstellar environment. It will also take the first global images of the boundary region of the heliosphere at 100 to 150 AU. These measurements will allow ISP to answer fundamental questions about the origin of the solar system and the stars, about the evolution of our galaxy and of the universe, and about the characteristics of our local galactic environment and its influence on the heliosphere. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618720

出版商:AIP    

年代:1903

数据来源: AIP