ISSN:0094-243X    

DOI:10.1063/1.1618531

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

In‐situ measurements of the solar wind began with simple ion traps on Soviet spacecraft in 1959. It wasn’t, however, until 1962 that the major properties of the solar wind were determined by Mariner 2. Improvements in instrumentation since then include the use of particle detectors, extension of the observations of the solar wind velocity vector to 2 or 3 dimensions, better time and energy resolution, greater variety of measurement locations, multipoint measurements, electron measurements, and the use of mass spectrometers and sample returns. This review summarizes what was learned about the solar wind from each of these improvements in instrumentation. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618532

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Even before the discovery of the fast solar wind in the mid ‐ 1970s, it was known that even the average solar wind could not be well explained by models in which electron heat conduction was the energy source and the electron pressure gradient was the principal accelerating force. The outward ‐ propagating Alfve´n waves discovered around 1970 were thought for a while to provide the sought ‐ after additional energy and momentum, but their wave pressure ultimately failed to explain the rapid acceleration of the fast wind close to the Sun in coronal holes. By the late 1970s, various in situ data were suggesting that protons and heavy ions were being heated and accelerated by the ion ‐ cyclotron resonance far from the Sun. This notion was soon applied to the acceleration region in coronal holes close to the Sun. The models which resulted suggested that the fast wind could be driven mainly by the proton pressure gradient (which is mainly the mirror force if the anisotropy is large), and that the high temperatures and flow speeds of heavy ions could originate within a few solar radii of the coronal base; these models also emphasized the importance of treating the extended coronal heating and solar wind acceleration on an equal footing. By the mid 1990s, SOHO, especially the UVCS (Ultraviolet Coronagraph Spectrometer), provided remarkable data which have given great impetus to studies of the ion cyclotron resonance as the principal mechanism for heating the plasma in coronal holes, and ultimately driving the fast wind. We will discuss the basic ideas behind current research, emphasizing the particle kinetics. We will discuss remaining problems such as the source of the ion ‐ cyclotron resonant waves (direct launching, turbulence, microinstabilities), problems concerning OVI and MgX, the roles of inward ‐ propagating waves and instabilities, the importance of oblique propagation, and the electron heating. Some alternatives, such as shock heating and turbulence ‐ driven magnetic reconnection, will also be reviewed. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618533

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Gas dynamic structure of the heliosphere is determined by the solar wind interaction with the supersonic flow of the partially ionized local interstellar medium (LISM). Historical review of this problem investigation is given here. General picture of the considered flow, a mathematical formulation of the gas‐kinetic model and its basic results are presented. It is shown that for forecasting of future experimental results it is necessary to construct the models with physically and mathematically correct theoretical basis. Examples of experimental data which can be explained on the basis of theoretical predictions are given. Results of the Ohm’s law analysis for partially ionized hydrogen gas show that a conception of the magnetic field freezing in plasma for the problem of the solar wind interaction with the magnetized LISM flow can be not correct if to take into account the processes of the resonance charge exchange. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618534

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Throughout declining and minimum phases of the solar cycle the solar wind displays a simple global structure with fast, tenuous flows emanating from large polar coronal holes filling the interplanetary medium at mid and high latitudes, and slower, denser, and much more variable flows at low latitudes. Approaching solar maximum a complicated mixture of flows from streamers, small coronal holes, and coronal mass ejections extends to higher and higher heliolatitudes, ultimately covering even the poles as the polar coronal holes shrink, fragment, and disappear. The most recent observations have continued through solar cycle 23 maximum with the formation of a mid‐sized, circumpolar coronal hole in the northern hemisphere. By April of 2002, Ulysses had again moved back down to ∼45° N, however, this hole has not yet grown to nearly the size of those observed in the previous orbit nor pushed fast solar wind down to mid‐latitudes. Rather, a complex mixture of solar wind flows is observed below ∼70° N in these recent observations. This interval also provided a unique geometry where Ulysses skimmed along, nearly parallel to the boundary of the polar coronal hole over several solar rotations. These times contain substantial intermediate speed solar wind, supporting the previous findings of McComas et al. [2002a] of thin boundary layers (CHBLs) flanking coronal holes. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618535

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The paper analyzes the magnetic field strength B and polarity observed in the distant heliosphere from 1996 to early 2001 and will be discussed in relation to the variation of B from 1978 through 1996. The observations extend the results of Burlaga et al. [1]. The polarity of the heliospheric magnetic field (HMF) from 1997 to early 2001 is studied in relation to the extrapolated position of the heliospheric current sheet (HCS). These observations of polarity extend the earlier results of Burlaga et al. [2] and Burlaga and Ness [3]. The V1 observations of the heliospheric magnetic field strength B agree with Parker’s model of the global heliospheric magnetic field from 1 to 81 AU and from 1978 to 2001, when one considers the solar cycle variations in the source magnetic field strength and the latitude/time variation in the solar wind speed. Parker’s model, without adjustable parameters, describe the general tendency for B to decrease with increasing distance R from the Sun, and the solar cycle time variations causing the three broad increases of B around 1980, 1990, and 2000, and the minima of B in 1987 and 1997. The variation of magnetic polarity observed by V1 and V2 was caused by the increasing latitudinal width of the sector zone with increasing solar activity, which in turn was related to the increasing maximum latitudinal extent and the decreasing minimum latitudinal extent of the footpoints of the HCS. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618536

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The LASCO C2 and C3 coronagraphs on SOHO have been recording a regular series of images of the corona since May 1996. This sequence of data covers the period of solar minimum, the increase to solar maximum, and the beginning of the decline toward the next solar minimum. The images have been analyzed to determine the brightness of the K‐corona (solar photons Thomson scattered from free electrons). The total brightness of the K‐corona is approximately constant from May 1996 through May 1997. The brightness is then seen to increase steadily until early in the year 2000. The structure of the K‐corona changes dramatically with solar cycle. The shape as seen in C2 becomes almost circular at solar maximum while the C3 images continue to show equatorial streamers. The magnitude of the solar cycle variation decreases as the height increases. We present data animations (movies) to show the large‐scale structure. We have inverted 28‐day averages of the white light images to determine radial profiles of electron density. We present these electron profiles, show how they vary as a function of both latitude and time, and compare our observed profiles with other models and observations. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618537

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

During the recent solar maximum, Voyager 1 was beyond 80 AU. Extrapolation of the small gradients of anomalous cosmic rays at solar minimum and the larger gradients at solar maximum indicate that the solar wind termination shock is at ≲ 92 AU at the beginning of 2002. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618538

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Previous studies of the source regions of solar wind sampled by ACE and Ulysses showed that some solar wind originates from open flux areas in active regions. These sources were labeledactive region sourceswhen there was no corresponding coronal hole in the He 10830 Å synoptic maps. Here, we present results on an investigation of the magnetic topology of these active region sources and a search for corresponding features in EUV and soft X‐ray images. In most, but not all, cases, a dark hole or lane is seen in the EUV and SXT image as for familiar coronal hole sources. However, in one case, the soft‐X ray images and the magnetic model showed a coronal structure quite different from typical coronal hole structure. Using ACE data, we also find that the solar wind from these active region sources generally has a higher Oxygen charge state than wind from the Helium‐10830Å coronal hole sources, indicating a hotter source region, consistent with the active region source interpretation. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618539

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The notion that density structure reflects magnetic field lines makes it possible to deduce information on coronal magnetic fields from density measurements. The purpose of this paper is to summarize the observational evidence for ubiquitous open magnetic field lines in the inner corona from density measurements. Based on both global and filamentary structures, these density measurements explain the unexpected predominance of the radial component of coronal magnetic field discovered in polarimetric observations over three decades ago. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618540

出版商:AIP    

年代:1903

数据来源: AIP