摘要:

The quiet corona at times close to solar minimum shows a striking north-south asymmetry which suggests that neither dipole-like nor octupole-like fields are sufficient to describe the global coronal magnetic field. We believe that such phenomena reflect the asymmetry of the intrinsic magnetic field of the sun as a star; this weak field is usually obscured by active regions. Empirical models for spherical corona (at solar maximum) and for ellipsoidal corona (at solar minimum) have been established. We extend the existing classification to include an empirical model for the quiet solar corona with strong north-south asymmetry. We show examples of such asymmetric corona in the green line for three different solar minima and evolution of corona from almost ellipsoidal type to corona with strong north-south asymmetry “bald man with double beard”). A theoretical model (1984) of Osherovich et al. (1) relates such asymmetry to the existence of a significant quadrupole term in the global magnetic field of the sun. According to this model, the size of northern and southern polar coronal holes is affected differently by a quadrupole term which creates asymmetry in the magnetic and thermodynamic parameters as well as in the velocity of the outflow from the two polar regions. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58823

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The source region of the slow solar wind is complicated by the fact that it is apparently located at the boundary between the helmet streamer belt arcade and adjacent polar coronal holes. This location implies that it should occupy the same region of heliospheric space as transients associated with CMEs, and may in fact consist partly of slow transients. Here we suggest a way to visualize the transient source using sequential potential field source surface models of the coronal magnetic field. We also suggest how future analysis of heat flux electron anisotropies could be used to empirically determine the transient contribution to the slow solar wind. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58824

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The Advanced Composition Explorer (ACE) spacecraft provides nearly continuous monitoring of solar wind plasma, magnetic fields, and energetic particles from the Sun-Earth L1 Lagrange point upstream of Earth in the solar wind. The Space Environment Center (SEC) in Boulder receives ACE telemetry from a group of international network of tracking stations. One-minute, and 1-hour averages of solar wind speed, density, temperature, and magnetic field components are posted on SEC’s World Wide Web page within 3 to 5 minutes after they are measured. The ACE Real Time Solar Wind (RTSW) can be used to provide real-time warnings and short term forecasts of geomagnetic storms based on the (traditional) Kp index. Here, we use historical data to evaluate the performance of the first real-time Kp prediction algorithm to become operational. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58720

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

In situsolar wind observations and solar observations from space enable us to investigate interplanetary disturbances and their solar sources. Recurrent high-speed streams from coronal holes around the solar minimum of cycle 22 have been observed. However, many geomagnetic storms are associated with CMEs even at the solar minimum. Coronal mass ejections (CMEs) have sometimes been observed in these high-speed streams. Geomagnetic storms associated with CMEs tend to be strong disturbances with short duration. Those associated with high-speed streams tend to be moderate disturbances with long duration. Both characteristics are seen in geomagnetic disturbances associated with both high-speed streams and CMEs. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58721

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Major non-recurrent geomagnetic storms are generally associated with solar wind (SW) disturbances created by fast coronal mass ejections (CMEs), and most major solar energetic proton events observed near Earth appear to result from the acceleration of SW particles by a CME-driven interplanetary shock (e.g. (1)). We present here a simplified theoretical model which describes the injection of particles and their subsequent acceleration at a fast CME associated shock. The model is fully time-dependent and the particle shock acceleration processes are described dynamically. Energetic or accelerated particles are allowed to escape at same distance upstream of the shock, after which they propagate scatter-free to an observation point. Dynamic spectra and intensity profile are presented. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58722

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Transient interplanetary shocks distort the interplanetary magnetic field as they propagate through the interplanetary medium. This distortion involves a deformation of the magnetic field lines and a modification of the magnetic field strength. Both factors have influence on the propagation of energetic particles. Magnetic trap regions, for instance, may appear around local minima of the magnetic field in the downstream region. We briefly discuss the problems that appear when modeling the transport of particles there, and we present a simplified model to describe the influence of the focusing effect on particle propagation. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58723

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We describe magnetic field, proton, electron, and &agr;-particle observations made by WIND on 24–25 October, 1995 of a structure consisting of a magnetic flux rope containing a relatively low beta plasma. While the flux rope structure was inferred from the magnetic field data, the particle behavior corroborates the inference. Minimum variance analysis of the magnetic field data indicates an axis highly inclined to the ecliptic plane and pointing away from the Sun-Earth line. The diameter of the flux rope is estimated as 0.07 AU. Despite a pronounced overpressure, the structure is not expanding but is rather being convected passively with the ambient flow. An intense antisunward field-aligned flow of heat flux electrons indicates that the flux rope is connected at one end to the Sun. The field variation is suggestive of a magnetic flux rope of constant field line twist, and a least-squares fit of this model to the data confirms this to a good approximation. The field line twist per unit length is estimated as ∼47 rad AU−1, so that assuming an orientation along the Parker spiral, a given field line has wound ∼10 times around the axis from the Sun to 1 AU. In a region inside the tube, the protons, electrons, and alpha particles are hot, the &agr;-to-proton temperature and density ratios are higher than the surroundings, and the &agr;-particles are slower than the protons. Electron and proton anisotropies are negative there(T⊥<T∥).The flux rope does not appear to be related to coronal mass ejections. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58724

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Following our long-term solar corona study program, we organized an expedition to the Curacao island (Dutch Antillas) to observe the total solar eclipse of February 26th, 1998. As the duration of this totality was quite short, our polarized white-light CCD imaging experiment was redesigned in order to increase the number of recorded images, thereby increasing the number of sampled polarization angles and exposures. This was made possible by upgrading to a new PC system, with fast hard disc and data transfer port. This allowed us to finally record 7 series of different exposures, each containing 24 images taken at 12 polarization angles, i.e. with 8-time oversampling. The data were processed to derive global maps of brightness and polarization, and from these, to build electron density models. In those maps, the shape of the corona is highly flattened, with extended polar holes filled with numerous wide plumes. All large streamers are essentially aligned along the solar equatorial plane. Moreover, the measured degree of polarization indicates that these structures are located in the vicinity of the plane of the sky. Unfortunately, the unusually high sky brightness hid the faint extensions of coronal structures. This limited their visibility to less than 3 solar radii, implying a corresponding limitation in the radial extent of our global model. The results presented here are also briefly compared with our earlier eclipse observations. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58725

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Eclipse line profiles of the E-corona (emission line corona) can provide direct data about velocity field in the range2–4R⊙which seems to be the most interesting in sense of searching the regions of the solar wind acceleration. As a rule, totality sky brightness is significantly reduced resulting in imitation of space-borne conditions. This allows to record line profiles at far distances. Eclipse “green” line (FeXIV5303 Å) Fabry-Perot interferograms obtained in 1981 and 1994 revealed fringes at distances of1.1–1.5R⊙.Traces of faint emission is seen up to 1.8R⊙for the 1981 corona. Reliable profiles corrected for the input of the white-light corona and instrumental effects were selected for analysis of distributions of the line full width at half maximum (FWHM). Both monotone and multimodal distributions are found for the whole corona for maximum and declining phases of solar activity. Hower, different coronal structures show similar quasi-monotone distributions. AverageFWHMof 0.8 Å, 0.9 Å, and 1.0 Å are found for streamers above active regions, helmets, and hole respectively. Performances of a portable eclipse instrumentation to get direct spectra in the range1.5–4R⊙are presented. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58802

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We present a 1-D, steady state MHD model of the pickup proton solar wind in the upwind direction. The model includes the kinetic theory solution of interstellar neutral hydrogen, the ionization process for the production of pickup protons, and the full MHD equations. The solution agrees reasonably well with the solar wind proton parameters obtained from Voyager 2 data. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58726

出版商:AIP    

年代:1999

数据来源: AIP