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1.
We compared the H I Lyα polar coronal hole profiles obtained during the three Spartan 201 flights (in 1993, 1994, and 1995) and during the more recent UVCS/SOHO mission. We found that at 2.1 R there are no significant variations of the line shape over the several years of the descending phase of the solar cycle. However, there may be some evidence for the 1.8 R profiles being broader towards solar minimum. The profiles at 2.1 R are different from profiles obtained at 1.8 R; they have clearly narrower cores and wide wings. We fitted the profiles with single and/or multiple Gaussian functions and calculated their typical 1/e half widths. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

2.
We analyzed UVCS/SOHO data and compared the H I Lyα (121.6 nm) and O VI (103.2 nm, 103.7 nm) emission in the polar and equatorial coronal holes. We found that the emission lines have similar characteristics in these two types of coronal holes. Both types show evidence for superradially diverging boundaries. The latitudinal distribution of the O VI line ratio may indicate that the equatorial coronal hole has O+5 outflow velocities lower than in the polar coronal holes. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

3.
Magneto-gravity Waves Trapped in the Lower Solar Corona   总被引:1,自引:0,他引:1  
The possibility of trapped magneto-gravity waves in the lower solar corona with an open magnetic field is discussed. Intensity variations and/or Doppler shifts of relevant UV, EUV and x-ray spectral lines in the chromosphere, transition region and lower corona may reveal the existence of such low-frequency modes (with periods longer than ∼ 1.5 hour). The spectrum may be either discrete or continuous depending on the reflection property of the narrow transition region. These modes can be utilized to probe the dynamics of the upper chromosphere, transition region and lower corona; they may also play an important role in coronal heating. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

4.
Polar coronal holes represent the most convincing site from which the high-speed solar wind originates. Here we report high-accuracy Doppler shifts measured in the O VI (1037.6 Å) line obtained by SUMER on SOHO inside an interplume region within the south polar coronal hole. We infer limits on the outflow velocity and draw hints about the flow geometry.  相似文献   

5.
Theories and observations of energy input, heating and acceleration mechanisms in the low corona were presented and discussed. The main topics of discussion were large-scale solar wind simulations, theoretical heating mechanisms, observational constraints, confronting theory with observations and observational issues. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

6.
Research into the heliospheric structure and its relation to the solar boundary is at an impasse. After successful predictions by Parker about the zeroth-order behavior of the heliospheric magnetic field and the solar wind, the heliospheric community struggles to make substantive progress toward a predictive model describing the connections between the Sun and its space environment, between the closed corona and the open corona extending to the planets. This is caused by our lack of understanding of the basic processes heating the corona and transporting open magnetic field. We detail the models used to describe this connectivity, from potential field source surface models to full MHD techniques. We discuss the current limitations of both approaches. Finally, we address a recent attempt to advance our understanding beyond these limitations. At this point in time the proposed theory remains controversial in the community, but it addresses important shortcomings of current approaches outlined above.  相似文献   

7.
The Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO) has been used to measure spectral line profiles for H I Lyα in the south polar coronal hole at projected heliocentric heights from 3.5 to 6.0 R during 1998 January 5–11. Observations from 1.5 to 2.5 R were made for comparison. The H I Lyα profile is the only one observable with UVCS above 3.5 R in coronal holes. Within this region the outflowing coronal plasma becomes nearly collisionless and the ionization balance is believed to become frozen. In this paper, the 1/e half widths of the coronal velocity distributions are provided for the observed heights. The velocity distributions include all motions contributing to the velocities along the line of sight (LOS). The observations have been corrected for instrumental effects and interplanetary H I Lyα. The half widths were found to increase with projected heliographic height from 1.5 to 2.5 R and decrease with height from 3.5 to 5 R. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

8.
The possibility of remote diagnostics of coronal structures with impulsively-generated short-period fast magnetoacoustic wave trains is demonstrated. An initially broad-band, aperiodic fast magnetoacoustic perturbation guided by a 1D plasma inhomogeneity develops into a quasi-periodic wave train with a well-pronounced frequency and amplitude modulation. The quasi-periodicity results from the geometrical dispersion of the modes, determined by the transverse profile of the loop, and hence contains information about the profile. Wavelet images of the wave train demonstrate that their typical spectral signature is of a “crazy tadpole’’ shape: a narrow spectrum tail precedes a broad-band head. The instantaneous period of the oscillations in the wave train decreases gradually with time, with a mean value of several seconds for typical coronal values. The period and the spectral amplitude evolution are determined by the steepness of the transverse density profile and the density contrast ratio in the loop, which offers a tool for estimation of the sub-resolution structuring of the corona.  相似文献   

9.
    
Coronal hole boundaries are the interfaces between regions where the coronal magnetic field contains a significant component which is open into the heliosphere and regions where the field is primarily closed. It is pointed out that there are constraints on the magnetic field which opens into the heliosphere that must be satisfied in the corona: it must come into pressure equilibrium in the high corona, and the component of the field which connects to the polar regions of the Sun must differentially rotate. A model is presented in which satisfying these constraints determines which field lines are open and which are closed, and thus where the polar coronal hole boundaries occur. Some of the consequences of this model are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

10.
We provide a brief overview of present-day studies of inner corona dynamics, with examples of mass ejections (CME), flares and active region dynamics. While the names of the topics have not changed in several decades, the internal details and the language used to express the nature of the problem have changed considerably. We conclude with a short discussion of the contribution to studies of coronal dynamics to be expected from the Atmospheric Imager Assembly (AIA) on the Solar Dynamics Observatory.  相似文献   

11.
A two dimensional model of the transition region and the lower corona, based on the idea that the magnetic flux is strongly concentrated at the boundaries of the supergranular convection cells, has been proposed by Gabriel in 1976. The plasma moves along the open magnetic field lines, which define the the so-called "funnel," and eventually builds up the solar wind. Based on a two dimensional funnel model we investigate the stationary plasma flow at its central line, taking heat conduction, radiative losses, and a heating function into account. The derived height profiles of the plasma properties within the funnel are presented. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

12.
    
Coronal holes have been identified as source regions of the fast solar wind, and MHD wave activity has been detected in coronal holes by remote sensing, and in situ in fast solar wind streams. I review some of the most suggestive wave observations, and discuss the theoretical aspects of MHD wave heating and solar wind acceleration in coronal holes. I review the results of single fluid 2.5D MHD, as well as multi-fluid 2.5D MHD models of waves in coronal holes, the heating, and the acceleration of the solar wind be these waves.  相似文献   

13.
    
Summarized below are the discussions of working group 3 on \"Coronal hole boundaries and interactions with adjacent regions\" which took place at the 7th SOHO workshop in Northeast Harbor, Maine, USA, 28 September to 1 October 1998. A number of recent observational and theoretical results were presented during the discussions to shed light on different aspects of coronal hole boundaries. The working group also included presentations on streamers and coronal holes to emphasis the difference between the plasma properties in these regions, and to serve as guidelines for the definition of the boundaries. Observations, particularly white light observations, show that multiple streamers are present close to the solar limb at all times. At some distance from the sun, typically below 2 R, these streamers merge into a relatively narrow sheet as seen, for example, in LASCO and UVCS images. The presence of multiple current sheets in interplanetary space was also briefly addressed. Coronal hole boundaries were defined as the abrupt transition from the bright appearing plasma sheet to the dark coronal hole regions. Observations in the inner corona seem to indicate a transition of typically 10 to 20 degrees, whereas observations in interplanetary space, carried out from Ulysses, show on one hand an even faster transition of less than 2 degrees which is in agreement with earlier Helios results. On the other hand, these observations also show that the transition happens on different scales, some of which are significantly larger. The slow solar wind is connected to the streamer belt/plasma sheet, even though the discussions were still not conclusive on the point where exactly the slow solar wind originates. Considered the high variability of plasma characteristics in slow wind streams, it seems most likely that several types of coronal regions produce slow solar wind, such as streamer stalks, streamer legs and open field regions between active regions, and maybe even regions just inside of the coronal holes. Observational and theoretical studies presented during the discussions show evidence that each of these regions may indeed contribute to the solar slow wind. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

14.
The transition between coronal hole associated fast solar wind and slow solar wind is studied using data from the high resolution mass spectrometer SWICS on ACE. We discuss the data in the framework of a recent theory about the global heliospheric magnetic field and conclude that the data are consistent with magnetic connections between field-lines in the fast and in the slow wind. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

15.
Spectra from the Coronal Diagnostic Spectrometer on board SOHO are used to compare density and temperature in coronal hole and quiet Sun regions. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

16.
An equatorial coronal hole has been observed on 18 and 19 October 1996 with SOHO-CDS and with the Nancąy Radioheliograph (RH). The CDS EUV line intensities are used to determine the coronal hole Differential Emission Measure (DEM); in turn this is used to compute the radio brightness temperature Tb at the observed frequencies, leaving the coronal electron temperature and density as free parameters. EUV line intensities, calculated from the derived models, show a good agreement with EUV observations. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

17.
    
In this paper I will briefly summarize the present status of our knowledge on the four different sorts of solar wind, their sources and their short- and long-term variations. First: the fast solar wind in high-speed streams that emerges from coronal hole regions. Second: the slow solar wind emerging from the non-active Sun near the global heliospheric current sheet above helmet streamers and underlying active regions. Third: the slow solar wind filling most of the heliosphere during high solar activity, emerging above active regions in a highly turbulent state, and fourth: the plasma expelled from the Sun during coronal mass ejections. The coronal sources of these different flows vary dramatically with the solar activity cycle.  相似文献   

18.
The dynamics of the solar corona as observed during solar minimum with the Ultraviolet Coronagraph Spectrometer, UVCS, on SOHO is discussed. The large quiescent coronal streamers existing during this phase of the solar cycle are very likely composed by sub-streamers, formed by closed loops and separated by open field lines that are channelling a slow plasma that flows close to the heliospheric current sheet. The polar coronal holes, with magnetic topology significantly varying from their core to their edges, emit fast wind in their central region and slow wind close to the streamer boundary. The transition from fast to slow wind then appears to be gradual in the corona, in contrast with the sharp transition between the two wind regimes observed in the heliosphere. It is suggested that speed, abundance and kinetic energy of the wind are modulated by the topology of the coronal magnetic field. Energy deposition occurs both in the slow and fast wind but its effect on the kinetic temperature and expansion rate is different for the slow and fast wind.  相似文献   

19.
We investigate the possibility of observing the effects of magnetic reconnection inside a current sheet forming in a coronal streamer in the extended corona. In particular we study the possibility to observe with the UVCS of SOHO the excitation of the tearing instability in the current sheet.  相似文献   

20.
SOHO: The Solar and Heliospheric Observatory   总被引:1,自引:0,他引:1  
The Solar and Heliospheric Observatory (SOHO), together with the Cluster mission, constitutes ESA's Solar Terrestrial Science Programme (STSP), the first Cornerstone of the Agency's long-term programme Space Science — Horizon 2000. STSP, which is being developed in a strong collaborative effort with NASA, will allow comprehensive studies to be made of the both the Sun's interior and its outer atmosphere, the acceleration and propagation of the solar wind and its interaction with the Earth. This paper gives a brief overview of one part of STSP, the SOHO mission.  相似文献   

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