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1.
In this study we analyse the positions of major flares from 1978 and 1979, with respect to the magnetic structure of the solar corona, as described by a potential field model. We find that major flares exhibit no strong association with the neutral line at the chromospheric level. However, when we calculate the neutral line's position at higher and higher altitudes in the corona, we find that major flares show an increasing tendency to be found close to these high-altitude coronal neutral lines. The correlation between flares and higher-altitude coronal neutral lines reaches a maximum at an altitude of 0.35R , and thereafter decreases as the neutral line is moved out to the source surface at an altitude of 1.50R . This indicates that major flares are strongly associated with coronal structure at the 0.35R level ( 250 000 km) - an altitude surprisingly high in the corona. This reinforces the idea that flares are associated with large-scale coronal magnetic fields and also indicates that the region of coronal magnetic topology important to solar flare processes may be larger than previously thought.  相似文献   

2.
Koomen  M. J.  Howard  R. A.  Michels  D. J. 《Solar physics》1998,180(1-2):247-263
The Naval Research Laboratory (NRL) Solwind coronagraph recorded the outer corona at elongations 2_5 R to 10 R during the 6 1/2-year interval from March 1979, before solar maximum, to the beginning of solar minimum in September 1985. During the minimum period, when the solar magnetic field was dipole-like, the observed corona consisted of the equatorial streamer belt that is characteristic of solar minimum, and that is interpreted as an edgewise view of a nearly flat current sheet or coronal disk lying near the plane of the heliographic equator. The observed disk was a radial projection from the magnetic neutral line that was computed for the 2.5 R source surface surrounding the Sun. At earlier times, shortly after solar maximum, the observed corona often consisted of a single coronal disk similar to that at solar minimum, but strongly tilted to the heliographic equator. Again this disk projected from a tilted magnetic neutral line that was computed for the 2.5 R source surface. Solar rotation allowed this coronal disk to be viewed in all aspects. In the edgewise view it appeared as a tilted streamer belt. In the broadside view the more flower-like pattern of solar maximum was observed. The latter view was interpreted as a non-uniform distribution of coronal material in the thin coronal disk. There were many intervals during the declining phase of the solar cycle when the computed magnetic neutral line at 2.5 R remained relatively simple but was not the source of an observable coronal disk. This latter result was probably because of the limitations of plane-of-sky observations, combined with short-term changes in the corona. Altogether, a single coronal disk, either flat or somewhat convoluted, was recognizable during only one third of the year lifetime of the coronagraph.  相似文献   

3.
A database is compiled for the study of solar and heliospheric causes of geomagnetic perturbations with the daily average index A > 20 that were observed in the period 1997–2000. The number of such events (more than 200) progressively increased and fluctuated as the current solar cycle developed. It is established that geomagnetic storms are generated by dynamical processes and structures near the center of the solar disk in a zone of several tens of degrees, and these processes are responsible for the appearance in the Earth's region, within several tens of hours, of quasistationary and transient solar wind streams with a sufficiently strong southward component of the heliospheric magnetic field. These streams lasted more than a few hours. The following structures can serve as morphological indicators for the prediction of the appearance of such streams: (1) active and disappearing filaments derived from synoptic -maps of the Sun, (2) solar flares, (3) coronal holes and evolving active regions, and (4) the heliospheric current sheet. The geometry of coronal mass ejections needs further observational study.  相似文献   

4.
During the total solar eclipse, 1965 May 30, a 25 cm aperturef/8.0 telescope and Fabry-Perot interferometer were operated aboard the USAF-AEC aircraft. High resolution spectra of the Fexiv emission line, 530.3 nm, were obtained. Deconvolved intensity vs wavelength profiles of the second order fringe overlay a helmet structure on the NM limb at out to 1.37R . The profiles yield coronal temperatures, absolute intensities and Doppler velocities in regions of apparently open magnetic field structure and within the closed field lines of the helmet. Together with white light intensities the observations are interpreted to provide temperatures and turbulent velocities in and around this coronal structure. Comparison is made with a model by Billings and Roberts. We suggest a model with radial flow (solar wind) velocities of 60 km s–1 satisfies the observations in the open field line region.Work performed under the auspices of the U.S. Atomic Energy Commission, and portions of the analysis at the National Center for Atmospheric Research, Boulder, Colo.  相似文献   

5.
We propose that the coronal source longitude and latitude of solar wind plasma can be estimated within 10°. Previous writers have argued that the solar wind in the ecliptic should originate near the equator and that a quasi-radial hypervelocity (QRH) approximation (constant radial flow) is valid beyond the magnetohydrodynamic critical points. We demonstrate that an extension of the QRH approximation (as if the solar wind flowed radially with constant velocity from the center of the Sun) yields a proper estimate of the high coronal source location at the release zone where the solar wind makes its transition to radial interplanetary flow. This extrapolated QRH (or EQRH) approximation succeeds because the two main corrections to this source estimate, coronal corotation and interplanetary acceleration, tend to cancel (the former correcting the source location eastward, the latter westward). Although this ideal spiral approximation was first suggested by Snyder and Neugebauer (1966), only recently has it been demonstrated that it relates a wide range of interplanetary plasma, magnetic field and energetic particle data to observed coronal magnetic structure. We estimate quantitatively the error in the EQRH approximation by comparison with steady-state streamlines predicted by azimuthally independent and dependent theoretical solutions to the steady-state plasma equations. We find the error in both cases 10° in longitude and therefore suggest that the EQRH approximation offers the means to relate observed solar initial conditions in the release zone directly to interplanetary measurements. If, in addition, the EQRH approximation also leads to agreement with low coronal structure, then there should be a straightforward correspondence to otherwise unobservable high coronal structure.  相似文献   

6.
Fainshtein  V. G. 《Solar physics》1997,174(1-2):413-435
This paper deals with the influence of the distance of the apparent axes of coronal mass ejections (CMEs) from a neutral line (NL) on the source surface and of coronal hole (CH) boundaries upon apparent characteristics of CMEs: e.g., the structure, the velocity of individual features, and the width.(a) It is found that the chance of measuring a CME velocity of ascent appears to decrease with increasing distance from a neutral line or coronal hole.(b) The apparent velocity of a CME appears to depend on the distance of its core from a neutral line or coronal hole boundary. CME speeds for events within 15 deg of a surface neutral line are significantly higher than those apparently much farther from surface neutral lines.(c) CME spans tend to be wider when they are more closely associated with surface neutral lines. It is shown that the contribution of CMEs in the neighbourhood of the NL (the heliomagnetic latitude of the CME apparent axis L < 15 deg) decreases with increasing length of the chain of coronal streamers separating the CH of like polarity of the magnetic field and depends on the character of the relationship between CMEs and other forms of activity. The study revealed a concentration of the apparent axes of CMEs toward zero lines of the photospheric magnetic field from the J. M. Wilcox Solar Observatory at Stanford.  相似文献   

7.
We have examined the relationships among coronal holes (CHs), corotating interaction regions (CIRs), and geomagnetic storms in the period 1996?–?2003. We have identified 123 CIRs with forward and reverse shock or wave features in ACE and Wind data and have linked them to coronal holes shown in National Solar Observatory/Kitt Peak (NSO/KP) daily He i 10?830 Å maps considering the Sun?–?Earth transit time of the solar wind with the observed wind speed. A sample of 107 CH?–?CIR pairs is thus identified. We have examined the magnetic polarity, location, and area of the CHs as well as their association with geomagnetic storms (Dst≤?50 nT). For all pairs, the magnetic polarity of the CHs is found to be consistent with the sunward (or earthward) direction of the interplanetary magnetic fields (IMFs), which confirms the linkage between the CHs and the CIRs in the sample. Our statistical analysis shows that (1) the mean longitude of the center of CHs is about 8°E, (2) 74% of the CHs are located between 30°S and 30°N (i.e., mostly in the equatorial regions), (3) 46% of the CIRs are associated with geomagnetic storms, (4) the area of geoeffective coronal holes is found to be larger than 0.12% of the solar hemisphere area, and (5) the maximum convective electric field E y in the solar wind is much more highly correlated with the Dst index than any other solar or interplanetary parameter. In addition, we found that there is also a semiannual variation of CIR-associated geomagnetic storms and discovered new tendencies as follows: For negative-polarity coronal holes, the percentage (59%; 16 out of 27 events) of CIRs associated with geomagnetic storms in the first half of the year is much larger than that (25%; 6 out of 24 events) in the second half of the year and the occurrence percentage (63%; 15 out of 24 events) of CIR-associated storms in the southern hemisphere is significantly larger than that (26%; 7 out of 27 events) in the northern hemisphere. Positive-polarity coronal holes exhibit an opposite tendency.  相似文献   

8.
Lotova  N.A.  Obridko  V.N.  Vladimirskii  K.V.  Bird  M.K.  Pätzold  M.  Sieber  W.  Güsten  R.  Korelov  O.A. 《Solar physics》1999,189(2):387-398
Long-term scintillation measurements of the solar wind formation zone at solar elongations ranging from 1°–8° (Sun impact parameters: 4–30 R ) were recorded using the water maser source IRC-20431 at the wavelength =1.35 cm during its annual solar occultations in December 1981–1998. Dramatic changes in the spatial dependence of the scintillation index were recorded over the course of the 11-year solar cycle. Markedly diminished scattering, attributed to a pronounced heliolatitude effect, was observed at the closest solar approach distances in the years around solar activity minimum. From parallel investigations of the solar magnetic field structure it was determined that the field strength at the source of the solar wind streamlines is the governing factor for the solar wind acceleration process. Particularly apparent in the scintillation data during solar activity minimum is the increasing role of the polar coronal holes with their associated open magnetic field structure. The dependence of the solar scattering intensity on heliolatitude fades in the years of high solar activity as the level of scintillations increases at polar latitudes.  相似文献   

9.
A correlative study is made between inferred solar sources of high-speed solar wind streams and extended white-light coronal features. The solar wind data used in the study consists of 110 co-rotating high-speed plasma streams observed from spacecraft at 1 AU in the period February 1971-December 1974; the coronal data consists of 144 equatorward extensions of polar coronal holes and 15 equatorial coronal holes, derived fromK-coronometer maps of the white-light corona during the same period. Of 110 observed solar wind streams 88 could directly be associated with an equatorward extension of a polar-cap coronal hole and 14 could be associated with a low-latitude equatorial coronal hole. In 8 cases no visible coronal feature was identified. Of 144 identified polar-cap extensions 102 were associated with a high-speed stream observed at 1 AU; 19 coronal features were related in time to data gaps in the solar wind measurements, while 38 features did not give rise to solar wind streams observed at Earth orbit. The probability of an association depended on the heliographic co-latitude of a polar hole extension, being 50% for a polar lobe extending down to 45° co-latitude and 100% for a polar coronal hole extending to 80° co-latitude or more.Paper presented at the 11th European Regional Astronomical Meeting of the IAU on New Windows to the Univese, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.  相似文献   

10.
The numerical integration of hydrodynamics equations with an allowance for thermal conductivity was made using the temperature distribution in the corona situated above the active regions obtained from the damping time of solar radio bursts of Types III and V. It is essential that for the integration path serve the magnetic field lines along which exciters of bursts are moving and accelerated coronal plasma can move freely too.The main result is the discovery of such regions, where the high temperature gradient precludes the possibility of a continuous flow of coronal plasma. These regions, where intense heating and rapid acceleration of the coronal plasma take place, were situated at distances of about 2 R from the Sun's center. They probably possess the character of weak detonation waves. The waves of cooling can also be present in these regions of discontinuity of the flow. The observations of bursts of Type V at distances up to 6.3 R gives some evidence that discontinuities of flow of the solar wind of the same nature can possibly arise also in the more remote parts of the solar corona.It is important that the similar jumps of velocity and other parameters of coronal plasma were also discovered earlier in a quite independent way as a result of the interpretation of the solar radio echo data. It can be anticipated that the nonthermal heating of coronal plasma, which was postulated to remove discrepancies between the existing models and observations of solar wind, was localized mainly in these regions thus playing an important role in the formation of the fundamental properties of the interplanetary medium.The obtained results are of preliminary character since there are no reliable and homogeneous data on bursts of Types III and V especially at 20-10 MHz, where the work is difficult due to the man-made interference and also at still lower frequencies, observed by the cosmic probes. We can hope that the filling of this gap allows us to construct a realistic model of outflow of coronal plasma from active regions, which can be successfully compared with the results of direct measurement of parameters of solar wind.  相似文献   

11.
Information concerning the coronal expansion is carried by solar wind heavy ions. Distinctly different energy-per-charge ion spectra are found in two classes of solar wind having the low kinetic temperatures necessary for E/q resolution of the ion species. Heavy ion spectra which can be resolved are most frequently observed in the low-speed interstream (IS) plasma found between high speed streams; the streams are thought to be coming from coronal holes. Although the sources of the IS plasma are uncertain, the heavy ion spectra found there contain identifiable peaks of O, Si, and Fe ions. Such spectra indicate that the IS ionization state of O is established in coronal gas at T 2.1 × 106 K while that of Fe is frozen in farther out at 1.5 × 106 K. On occasion anomalous spectra are found outside IS flows in solar wind with abnormally depressed local kinetic temperatures. The anomalous spectra contain Fe16+ ions, not usually found in IS flows, and the derived coronal freezing in temperatures are significantly higher; for two of the best cases values of 3.4 × 106 K were found for the O ions and 2.9 × 106 K for Fe ions. The coronal sources of some of these ionizationally hot flows are identified as solar flares. The appearance of abnormally depressed kinetic temperatures in solar wind coming from flare-heated coronal gas lends support to earlier speculation that flares can expel plasma enclosed in magnetic bottles or bubbles. In transit to 1 AU the gas is sufficiently isolated from the hot corona that it cools anomalously.The Los Alamos Scientific Laboratory requests that the publisher identify this article as work performed under the auspices of the Department of Energy.By acceptance of this article, the publisher recognizes that the U.S. Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or to allow others to do so, for U.S. Government purposes.  相似文献   

12.
A new relation has been given in order to calculate the intensity of the green line of the solar corona at 5303 Å as a function of the number of proton events N P and the R (R) index of solar activity. This relation is available for the 19th and 20th solar cycles. Moreover there is given a theoretical justification of this relationship taking into account as a new parameter the evolution of the coronal magnetic field during the solar cycle.  相似文献   

13.
The energy balance of open-field regions of the corona and solar wind and the influence of the flow geometry in the corona upon the density and temperature, are analyzed. It is found that the energy flux arriving at the corona is constant for the corona's open regions with different flow geometries. For the waves heating the corona and solar wind, the dependence of the absorption coefficient on the corona's plasma density is found to be within the range of distances r=1.05–1.5R . It is shown that the wave absorption is more dependent on electron density than the coronal emission. It is this difference that causes lower-density coronal holes to be colder than quiet regions. It is found that the additional energy flux necessary for providing energy balance of the corona and for producing solar wind is a flux of Alfvén waves, which can provide the energy needed for producing quasi-stationary high-speed solar wind streams. Theoretical models of coronal holes and the question of why the high-speed solar wind streams are precisely flowing out of coronal holes, are discussed.  相似文献   

14.
Interplanetary Scintillation (IPS) Observations were made during the period 1984–1990 using a single radio telescope at 103 MHz situated at Thaltej (Ahmedabad), India. Solar wind speeds were estimated using a recently developed method based on matching the observed IPS spectra with model solar wind spectra for Kolmogorov turbulence. The best-fit speeds derived are traced back to a source surface, and average velocity maps are made for each year, averaging over a number of Carrington rotations. It is found that the resulting single-site, large-scale IPS speed structure agrees well with that derived from 3-site observations from earlier workers. The IPS speed structure during this period was compared with other coronal features. Nearly 85% of the observed high-speed regions were associated with coronal holes. At solar minimum, in 1986, a quasi-sinusoidal, narrow belt of slow solar wind was observed which matched well with the neutral line structure of the solar magnetic field and the belt of active centers. Near solar maximum, in 1990, the speed structure was chaotic, similar to that of the neutral line, with low speed regions appearing all over the source surface.  相似文献   

15.
Solar Wind Forecasting with Coronal Holes   总被引：1，自引：0，他引：1  
An empirical model for forecasting solar wind speed related geomagnetic events is presented here. The model is based on the estimated location and size of solar coronal holes. This method differs from models that are based on photospheric magnetograms (e.g., Wang–Sheeley model) to estimate the open field line configuration. Rather than requiring the use of a full magnetic synoptic map, the method presented here can be used to forecast solar wind velocities and magnetic polarity from a single coronal hole image, along with a single magnetic full-disk image. The coronal hole parameters used in this study are estimated with Kitt Peak Vacuum Telescope He I 1083 nm spectrograms and photospheric magnetograms. Solar wind and coronal hole data for the period between May 1992 and September 2003 are investigated. The new model is found to be accurate to within 10% of observed solar wind measurements for its best 1-month period, and it has a linear correlation coefficient of ∼0.38 for the full 11 years studied. Using a single estimated coronal hole map, the model can forecast the Earth directed solar wind velocity up to 8.5 days in advance. In addition, this method can be used with any source of coronal hole area and location data.  相似文献   

16.
We observed Faraday rotation of linearly polarized radio waves from the Crab Nebula (Tau A) at 4170 MHz during solar coronal occultations in June 1971–75. Mean amplitudes of the variations of position angle are larger in an active phase of the solar cycle than in a quiet phase. In occultations in 1971 and 1973, the position angle of the polarization varied oscillatory by 20–50 degrees due to local magnetic structures in the corona with a typical scale-length of about 0.5 R . In 1974, we observed a typical variation of position angle of polarization which is expected from a Y-shaped field configuration in coronal streamers.The Faraday rotation is enhanced when the line of sight to Tau A passes through strong coronal magnetic fields computed from magnetograph observations, while the rotation is suppressed when the line of sight passes through large coronal holes observed in X-rays. Short-time oscillation of the rotation angle observed in 1971 and 1973 suggests that neutral sheets in coronal streamers oscillate at a period of 3 hours with an amplitude of 1 R at a distance of 10 R from the Sun.  相似文献   

17.
High resolution spectra of the coronal emission line Fe xiv at 530.3 nm obtained at the 30 May 1965 total solar eclipse are analyzed and interpreted. Deconvolution techniques that preserve the line intensity vs wavelength profile shape are developed to obtain further resolution improvement. The west limb coronal enhancement is determined to have temperatures less than 3 MK and turbulent velocities of ～25 km s-1 decreasing with altitude. Temperature gradients provide evidence for marginal solar wind flow from this enhancement. Above the quiet photosphere in the southwest quadrant the comparison of line and continuum intensities and consideration of line width suggest to us the coronal region is filled with inhomogeneous plasma, dense enough in localized regions to maintain collisional excitation. Solar wind flow from this region obtains when turbulent velocities are assumed to contribute to the line broadening. We identify this region as a coronal hole and suggest that coronal material is heated by the quiet photosphere below.  相似文献   

18.
We present observations of the corona at 169 MHz with the Nançay Radioheliograph during the summer of 1984. We compare synoptic maps of the metric radio emission on the solar disk with synoptic charts of the K-corona as well as of the green and the red lines. Local sources of radio emission are not located near regions of enhanced green or red line emission which, in turn, are in general above chromospheric faculae. Thus the radio emissions located in the surroundings of faculae are apparently related to different loop systems, with lower density. The comparison of the radio data with the K-corona showed one radio source associated with enhanced emission both at 1.3 and at 1.7 R , apparently a streamer. Other radio sources did not show any clear associations, but were nevertheless located within the coronal plasma sheet, delineated by the large-scale K-corona emission. Moreover the large-scale structure of the corona at 169 MHz was quite similar to the coronal plasma sheet observed at 1.3 R above the limb. The extent of the radio emission in latitude is very similar to that of the K-corona, while the coronal line emission is more concentrated near the solar equator.  相似文献   

19.
Observation of a possible neutral sheet in the corona   总被引：2，自引：0，他引：2  
John A. Eddy 《Solar physics》1973,30(2):385-394
A linear coronal ray, centered on a large helmet, is prominent in white-light photographs taken at the 1922 eclipse. It extends from near the limb to 4 R , has minimum width 9 arc, and persisted for at least 35 min. Examination reveals that the ray marks the cleavage between the domes of a twin-arch streamer which in turn is associated with two large, distinct chromospheric active regions. The ray is interpreted as the edge-on aspect of a coronal neutral sheet which separates areas of presumed opposite magnetic polarity in the two surface regions.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

20.
This paper is a qualitative study of 42 events of solar filament/prominence sudden disappearances (“disparitions brusques”; henceforth DBs) around two solar minima, 1985 – 1986 and 1994. The studied events were classified as 17 thermal and 25 dynamic disappearances. Associated events, i.e. coronal mass ejections (CMEs), type II bursts, evolution of nearby coronal holes, as well as solar wind speed, and geomagnetic disturbances are discussed. We have found that about 50% of the thermal DBs with adjacent (within 15° from the DB) coronal holes were associated with CMEs within a selected time window. All the studied thermal disappearances with adjacent coronal holes or accompanied by dynamic disappearances were associated with weak and medium geomagnetic storms. Also, nearly 64% of dynamic DBs were associated with CMEs. Ten (40%) dynamic disappearances were associated with intense geomagnetic storms, even when no CMEs was reported, six (24%) dynamic disappearances corresponded to extreme storms, and five (20%) corresponded to medium geomagnetic storms. The extreme geomagnetic storms appeared to be related to combined events, involving dynamic disappearances with adjacent coronal holes or including thermal disappearances. Furthermore, the geomagnetic activity (Dst index) increased if the source was close to the central meridian (±30°). The highest interplanetary magnetic field (B), longest duration, lowest southward direction B z component, and lowest Dst were highly correlated for all studied events. The Sun – Earth transit time computed from the starting time of the sudden disappearance and the time its effect was measured at Earth was about 4.3 days and was mainly well correlated with the solar wind speed measured in situ (daily value).  相似文献   

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