摘要:

We present the rationale andin situmeasurement requirements for a near-Sun mission intended to answer the central questions of the heating of the corona and the acceleration of the solar wind. These conclusions are based on panel discussions and presentations at the Marlboro workshop. We have in mind not a “minimum” mission [1], but rather one that is constrained but feasible within the current mass and telemetry rate restrictions. To distinguish between thermal, wave-driven, and microflare-driven models, the measurements must determine wave levels in a broad range of frequencies, resolve fine-scale structures, find the energetic particle content and its variations, and determine the bulk properties of a few species with detailed distributions for at least electrons and protons. We find that thein situmeasurements needed to answer the main questions are similar to those proposed previously [4] (magnetic field, plasma, high-energy particles, and plasma wave instruments) but without neutron and dust experiments. Telemetry and mass constraints will be significant but should not be prohibitive. ©1997 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.51764

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Remote-sensing observations of the Sun and inner heliosphere are reviewed to appraise our understanding of the mix of mechanisms that heat the corona and accelerate the solar wind. An assessment of experimental uncertainties and the basic assumptions needed to translate measurables into physical models, reveals very large fundamental uncertainties in our knowledge of coronal structure near the Sun. We develop a time-dependent, filamentary model of the extended corona that is consistent with a large number of remote sensing observations of the solar atmosphere and the solar wind. ©1997 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.51742

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In situ observations indicate that the low-speed wind is highly variable. It commonly originates on open field lines that thread coronal streamers in the vicinity of the magnetic equator, but transient ejections are also a source of low-speed flows on occasion. Close to the Sun a large flow shear probably is common at the interface between low- and high-speed flows. Near solar activity minimum low-speed flows are confined to a narrow band 40–45° wide centered roughly on the solar equator, but near solar maximum low-speed flows may dominate at all heliographic latitudes. ©1997 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.51743

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The current understanding of solar energetic particles in the interplanetary medium is reviewed, and recent observations from the Wind spacecraft presented. In impulsive events the electron energy spectrum is found to extend down in a power law to≲1 keV,implying that the source must be high,0.2–1 R⊙,in the corona. At solar quiet times Wind detects a continuously present “super-halo” component with approximately power law spectrum from∼1 keVto∼100 keV.What is known about energetic particles at Sun is summarized, and recent work on solar hard X-ray bursts observed down to∼7 keVis discussed. The energetic electrons accelerated in these frequently occurring hard x-ray microflares may contribute significantly to the heating of the active corona. ©1997 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.51744

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The fluctuations in solar-wind velocity measured by the Ulysses spacecraft above the polar regions of the Sun are organized into structures called microstreams. The application of wavelet transformations to the Ulysses data reveals the scales and positions of the microstreams and their association with variations in the helium content of the solar wind. It is concluded that the microstreams must have their origin in solar structures associated with the acceleration of the solar wind with little modification resulting from interplanetary phenomena. ©1997 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.51765

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Measurement of the spectrum of plasma waves in the solar corona is needed in order to answer questions on the nature of the plasma turbulence and energy transfer responsible for the high coronal temperatures. In planned solar probe missions, wave measurements at low frequency are important for understanding magnetohydrodynamic heating processes of the corona. Higher frequency plasma waves provide a relatively sensitive signature of the kinetic processes that may be involved in the heating, transport, and acceleration of particles. Because there have been no in situ measurements of the solar corona, the spectrum of plasma waves cannot be precisely predicted; however, experience with solar wind and magnetospheric experiments suggests that the very dynamic nature of the corona must lead to a wide range of plasma wave emissions. Indeed, the dynamic spectra of solar radio bursts received at earth are an indication that many plasma emission processes occur in the corona. It is therefore suggested that the plasma wave spectrum up to and above the local plasma frequency should be measured during future in situ missions. We discuss this approach to planned solar probe missions and suggest some of the experimental results that may be achieved. ©1997 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.51766

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An MHD model of a polar coronal hole based on white light coronagraph observations is used to make predictions of plasma observations in the spacecraft frame along the spacecraft trajectory for the Solar Probe Mission. This study will identify the design requirements for in situ plasma instrumentation with regard to field-of-view issues, energy coverage, instrument geometric factors and mass separation requirements. The instrument design must consider the need to accurately observe MHD wave motions in the plasma and electron heat flux both of which are thought to play an important role with regard to the coronal expansion. These requirements emphasize the need for 3-D plasma measurements and the requirement for nadir viewing. ©1997 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.51767

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Measurements of turbulence properties, including the degree of spectral anisotropy, are essential to the scientific objectives of the Solar Probe mission. Several types of measurements are discussed including component variances, reduced spectra, and helicities. The measurability of spectra with a single spacecraft depend upon some form of “frozen-in” approximation that allows conversion of frequency to wavenumber. Accuracy of several such approximations is examined along the proposed spacecraft trajectory. ©1997 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.51768

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Remote sensing measurements of the solar corona are indispensable for the exploration of the source and acceleration regions of the solar wind which are inaccessible to in situ plasma, particles and fields experiments. Furthermore, imaging the solar disk and corona from the unique vantage point of the trajectory and the proximity of the Solar Probe spacecraft, will provide the first ever opportunity to explore the small scale structures within coronal holes and streamers from viewing angles and with spatial resolutions never attained before. Imaging will also provide the essential context for the in situ measurements. The scientific advantages of different proposed imagers are summarized here. Both disk and limb observations are recommended. Given the power, weight and telemetry limitations of the Solar Probe, the optimal choice of imagers could not be provided at the time of the workshop. Further concentrated studies were highly recommended. ©1997 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.51769

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

While ray-like structures in the solar corona have been observed in white-light coronagraph and solar eclipse images for many years, recent progress using radio occultation measurements have revealed a plethora of structures extending to sizes as small as 1 km—three orders of magnitude smaller than those observed in white-light and eclipse measurements. Advances have also been made in understanding the variation of large- and small-scale structures in the extended corona and their organization by the heliospheric current sheet. This paper summarizes the latest results on the morphology of the near-Sun solar wind obtained from radio occultation measurements, and their impact on the planning and conduct of a mission to the Sun such as Solar Probe. ©1997 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.51770

出版商:AIP    

年代:1997

数据来源: AIP