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1.
This paper presents the results of polarization observations of asteroid 554 Peraga obtained with the UBVRI polarimeter using
the 1.25 m telescope of the Crimean Astrophysical Observatory down to phase angles of 3.1°–16.6° from October to November
2006. The asteroid’s polarization phase curve is shown to have a negative branch with the parameters P
min = −1.7% and αmin = 8.4°, which is typical of C-type asteroids. However, these data contradict the results of Zellner and Gradie (1976) obtained
in March 1975 that the reflected light from the asteroid’s surface is positively polarized, ≈1% at phase angles of 8°–10°.
Since the asteroid’s ecliptic longitudes differ by 160°-145° for the two observation periods, we discuss the possibility that
the two sets of observations refer to the asteroid’s two hemispheres with different polarimetric properties. 相似文献
2.
N. Lugaz 《Solar physics》2010,267(2):411-429
Using data from the Heliospheric Imagers (HIs) onboard STEREO, it is possible to derive the direction of propagation of coronal
mass ejections (CMEs) in addition to their speed with a variety of methods. For CMEs observed by both STEREO spacecraft, it
is possible to derive their direction using simultaneous observations from the twin spacecraft and also, using observations
from only one spacecraft with fitting methods. This makes it possible to test and compare different analysis techniques. In
this article, we propose a new fitting method based on observations from one spacecraft, which we compare to the commonly
used fitting method of Sheeley et al. (J. Geophys. Res.
104, 24739, 1999). We also compare the results from these two fitting methods with those from two stereoscopic methods, focusing on 12 CMEs
observed simultaneously by the two STEREO spacecraft in 2008 and 2009. We find evidence that the fitting method of Sheeley
et al. (J. Geophys. Res.
104, 24739, 1999) may result in significant errors in the determination of the CME direction when the CME propagates outside of 60°±20° from
the Sun – spacecraft line. We expect our new fitting method to be better adapted to the analysis of halo or limb CMEs with
respect to the observing spacecraft. We also find some evidence that direct triangulation in the HI fields-of-view should
only be applied to CMEs propagating approximatively toward Earth (± 20° from the Sun – Earth line). Last, we address one of
the possible sources of errors of fitting methods: the assumption of radial propagation. Using stereoscopic methods, we find
that at least seven of the 12 studied CMEs had a heliospheric deflection of less than 20° as they propagated in the HI fields-of-view,
which, we believe, validates this approximation. 相似文献
3.
R. P. Kane 《Solar physics》2008,249(2):369-380
The sunspot number series at the peak of sunspot activity often has two or three peaks (Gnevyshev peaks; Gnevyshev, Solar Phys.
1, 107, 1967; Solar Phys.
51, 175, 1977). The sunspot group number (SGN) data were examined for 1997 – 2003 (part of cycle 23) and compared with data for coronal
mass ejection (CME) events. It was noticed that they exhibited mostly two Gnevyshev peaks in each of the four latitude belts
0° – 10°, 10° – 20°, 20 ° – 30°, and > 30°, in both N (northern) and S (southern) solar hemispheres. The SGN were confined
to within latitudes ± 50° around the Equator, mostly around ± 35°, and seemed to occur later in lower latitudes, indicating
possible latitudinal migration as in the Maunder butterfly diagrams. In CMEs, less energetic CMEs (of widths < 71°) showed
prominent Gnevyshev peaks during sunspot maximum years in almost all latitude belts, including near the poles. The CME activity
lasted longer than the SGN activity. However, the CME peaks did not match the SGN peaks and were almost simultaneous at different
latitudes, indicating no latitudinal migration. In energetic CMEs including halo CMEs, the Gnevyshev peaks were obscure and
ill-defined. The solar polar magnetic fields show polarity reversal during sunspot maximum years, first at the North Pole
and, a few months later, at the South Pole. However, the CME peaks and gaps did not match with the magnetic field reversal
times, preceding them by several months, rendering any cause – effect relationship doubtful. 相似文献
4.
The Theory of Alfven drag (Drell et al. in J Geophys Res 70: 3131–3145 1965; Anselmo and Farinella in Icarus, 58, 182–185 1983) is applied here to show that the existence of a possible solar ring structure at a radial distance of 0.02 AU (~4R
⊙
, R
⊙
= radius of the sun) predicted by earlier authors (Brecher et al. in Nature 282, 50–52 1979; Rawal in Bull. Astr. Soc. India 6, 92–95 1978, Moon Planets 24, 407–414 1981, Moon Planets 31, 175–182 1984, J Astrophys Astr 10, 257–259 1989) may not survive Alfven drag produced during even moderate solar magnetic storms which take place from time to time through
the age of the sun, but a possible solar ring structure at a radial distance of 0.13 AU (~27R
⊙
) (Brecher et al. in Nature 282, 50–52 1979; Rawal in Bull. Astr. Soc. India 6, 92–95 1978, Moon Planets 24, 407–414 1981, Moon Planets 31, 175–182 1984, J Astrophys Astr 10, 257–259 1989) may survive intense Alfven drag produced during even strong magnetic storms of magnetic field value up to 1,000 G. 相似文献
5.
In the previous study (Dabas et al. in Solar Phys.
250, 171, 2008), to predict the maximum sunspot number of the current solar cycle 24 based on the geomagnetic activity of the preceding
sunspot minimum, the Ap index was used which is available from the last six to seven solar cycles. Since a longer series of the aa index is available for more than the last 10 – 12 cycles, the present study utilizes aa to validate the earlier prediction. Based on the same methodology, the disturbance index (DI), which is the 12-month moving
average of the number of disturbed days (aa≥50), is computed at thirteen selected times (called variate blocks 1,2,…,13; each of them in six-month duration) during the
declining portion of the ongoing sunspot cycle. Then its correlation with the maximum sunspot number of the following cycle
is evaluated. As in the case of Ap, variate block 9, which occurs exactly 48 months after the current cycle maximum, gives the best correlation (R=0.96) with a minimum standard error of estimation (SEE) of ± 9. As applied to cycle 24, the aa index as precursor yields the maximum sunspot number of about 120±16 (the 90% prediction interval), which is within the 90%
prediction interval of the earlier prediction (124±23 using Ap). Furthermore, the same method is applied to an expanded range of cycles 11 – 23, and once again variate block 9 gives the
best correlation (R=0.95) with a minimum SEE of ± 13. The relation yields the modified maximum amplitude for cycle 24 of about 131±20, which
is also close to our earlier prediction and is likely to occur at about 43±4 months after its minimum (December 2008), probably
in July 2012 (± 4 months). 相似文献
6.
R. P. Kane 《Solar physics》2007,246(2):471-485
Many methods of predictions of sunspot maximum number use data before or at the preceding sunspot minimum to correlate with
the following sunspot maximum of the same cycle, which occurs a few years later. Kane and Trivedi (Solar Phys. 68, 135, 1980) found that correlations of R
z(max) (the maximum in the 12-month running means of sunspot number R
z) with R
z(min) (the minimum in the 12-month running means of sunspot number R
z) in the solar latitude belt 20° – 40°, particularly in the southern hemisphere, exceeded 0.6 and was still higher (0.86)
for the narrower belt > 30° S. Recently, Javaraiah (Mon. Not. Roy. Astron. Soc.
377, L34, 2007) studied the relationship of sunspot areas at different solar latitudes and reported correlations 0.95 – 0.97 between minima and maxima of sunspot areas at low latitudes
and sunspot maxima of the next cycle, and predictions could be made with an antecedence of more than 11 years. For the present
study, we selected another parameter, namely, SGN, the sunspot group number (irrespective of their areas) and found that SGN(min) during a sunspot minimum year at latitudes > 30° S had a correlation
+0.78±0.11 with the sunspot number R
z(max) of the same cycle. Also, the SGN during a sunspot minimum year in the latitude belt (10° – 30° N) had a correlation +0.87±0.07 with the
sunspot number R
z(max) of the next cycle. We obtain an appropriate regression equation, from which our prediction for the coming cycle 24 is R
z(max )=129.7±16.3. 相似文献
7.
We present the first in-depth statistical survey of flare source heights observed by RHESSI. Flares were found using a flare-finding
algorithm designed to search the 6 – 10 keV count-rate when RHESSI’s full sensitivity was available in order to find the smallest
events (Christe et al. in Astrophys. J.
677, 1385, 2008). Between March 2002 and March 2007, a total of 25 006 events were found. Source locations were determined in the 4 – 10 keV,
10 – 15 keV, and 15 – 30 keV energy ranges for each event. In order to extract the height distribution from the observed projected
source positions, a forward-fit model was developed with an assumed source height distribution where height is measured from
the photosphere. We find that the best flare height distribution is given by g(h)∝exp (−h/λ) where λ=6.1±0.3 Mm is the scale height. A power-law height distribution with a negative power-law index, γ=3.1±0.1 is also consistent with the data. Interpreted as thermal loop-top sources, these heights are compared to loops generated
by a potential-field model (PFSS). The measured flare heights distribution are found to be much steeper than the potential-field
loop height distribution, which may be a signature of the flare energization process. 相似文献
8.
P. Rudawy K. J. H. Phillips A. Buczylko D. R. Williams F. P. Keenan 《Solar physics》2010,267(2):305-327
Some 8000 images obtained with the Solar Eclipse Coronal Imaging System (SECIS) fast-frame CCD camera instrument located at Lusaka, Zambia, during the total eclipse of 21 June 2001 have been analysed
to search for short-period oscillations in intensity that could be a signature of solar coronal heating mechanisms by MHD
wave dissipation. Images were taken in white-light and Fe xiv green-line (5303 ?) channels over 205 seconds (frame rate 39 s−1), approximately the length of eclipse totality at this location, with a pixel size of four arcseconds square. The data are
of considerably better quality than those that we obtained during the 11 August 1999 total eclipse (Rudawy et al.: Astron. Astrophys. 416, 1179, 2004), in that the images are much better exposed and enhancements in the drive system of the heliostat used gave a much improved
image stability. Classical Fourier and wavelet techniques have been used to analyse the emission at 29 518 locations, of which
10 714 had emission at reasonably high levels, searching for periodic fluctuations with periods in the range 0.1 – 17 seconds
(frequencies 0.06 – 10 Hz). While a number of possible periodicities were apparent in the wavelet analysis, none of the spatially
and time-limited periodicities in the local brightness curves was found to be physically important. This implies that the
pervasive Alfvén wave-like phenomena (Tomczyk et al.: Science
317, 1192, 2007) using polarimetric observations with the Coronal Multi-Channel Polarimeter (CoMP) instrument do not give rise to significant oscillatory intensity fluctuations. 相似文献
9.
We analyze the pulses in high-frequency drift radio structures observed by the spectrometer at Purple Mountain Observatory
(PMO) over the frequency range of 4.5 – 7.5 GHz during the 18 March 2003 solar flare. A number of individual pulses are determined
from the drifting radio structures after the detected gradual component subtraction. The frequency distributions of microwave
pulse occurrence as functions of peak flux, duration, bandwidth, and time interval between two adjacent pulses exhibit a power-law
behavior, i.e.
. From regression fitting in log-log space, we obtain the power-law indexes, α
P=7.38±0.40 for the peak flux, α
D=5.39±0.86 for the duration, and α
B=6.35±0.56 for the bandwidth. We find that the frequency distribution for the time interval displays a broken power law. The
break occurs at about 500 ms, and their indexes are α
W1=1.56±0.08 and α
W2=3.19±0.12, respectively. Our results are consistent with the previous findings of hard X-ray pulses, type III bursts, and
decimetric millisecond spikes. 相似文献
10.
J. Javaraiah 《Solar physics》2008,252(2):419-439
Recently, using Greenwich and Solar Optical Observing Network sunspot group data during the period 1874 – 2006, Javaraiah
(Mon. Not. Roy. Astron. Soc.
377, L34, 2007: Paper I), has found that: (1) the sum of the areas of the sunspot groups in 0° – 10° latitude interval of the Sun’s northern
hemisphere and in the time-interval of −1.35 year to +2.15 year from the time of the preceding minimum of a solar cycle n correlates well (corr. coeff. r=0.947) with the amplitude (maximum of the smoothed monthly sunspot number) of the next cycle n+1. (2) The sum of the areas of the spot groups in 0° – 10° latitude interval of the southern hemisphere and in the time-interval
of 1.0 year to 1.75 year just after the time of the maximum of the cycle n correlates very well (r=0.966) with the amplitude of cycle n+1. Using these relations, (1) and (2), the values 112±13 and 74±10, respectively, were predicted in Paper I for the amplitude
of the upcoming cycle 24. Here we found that the north – south asymmetries in the aforementioned area sums have a strong ≈44-year
periodicity and from this we can infer that the upcoming cycle 24 will be weaker than cycle 23. In case of (1), the north – south
asymmetry in the area sum of a cycle n also has a relationship, say (3), with the amplitude of cycle n+1, which is similar to (1) but more statistically significant (r=0.968) like (2). By using (3) it is possible to predict the amplitude of a cycle with a better accuracy by about 13 years
in advance, and we get 103±10 for the amplitude of the upcoming cycle 24. However, we found a similar but a more statistically
significant (r=0.983) relationship, say (4), by using the sum of the area sum used in (2) and the north – south difference used in (3).
By using (4) it is possible to predict the amplitude of a cycle by about 9 years in advance with a high accuracy and we get
87±7 for the amplitude of cycle 24, which is about 28% less than the amplitude of cycle 23. Our results also indicate that
cycle 25 will be stronger than cycle 24. The variations in the mean meridional motions of the spot groups during odd and even
numbered cycles suggest that the solar meridional flows may transport magnetic flux across the solar equator and potentially
responsible for all the above relationships.
The author did a major part of this work at the Department of Physics and Astronomy, UCLA, 430 Portola Plaza, Los Angeles,
CA 90095-1547, USA. 相似文献
11.
We studied the characteristics of the zebra-associated spike-like bursts that were recorded with high time resolution at 1420
MHz in four intervals (from 12:45 to 12:48 UT) during 5 August 2003. Our detailed analysis is based on the selection of more
than 500 such spike-like bursts and it is, at least to our knowledge, the first study devoted to such short-lived bursts.
Their characteristics are different from those pertinent to “normal” spike bursts, as presented in the paper by Güdel and
Benz (Astron. Astrophys.
231, 202, 1990); in particular, their duration (about 7.4 ms at half power) is shorter, so they should be members of the SSS (super short
structures) family (Magdalenić et al., Astrophys. J.
642, L77, 2006). The bursts were generally strongly R-polarized; however, during the decaying part of interval I a low R-polarized and L-polarized
bursts were also present. This change of polarization shows a trend that resembles the peculiar form of the zebra lines in
the spectral dominion (“V” like). A global statistical analysis on the bursts observed in the two polarimetric channels shows
that the highest cross-correlation coefficient (about 0.5) was pertinent to interval I. The zebras and the bursts can be interpreted
by the same double plasma resonance process as proposed by Bárta and Karlicky (Astron. Astrophys.
379, 1045, 2001) and Karlicky et al. (Astron. Astrophys.
375, 638, 2001); in particular, the spikes are generated by the interruption of this process by assumed turbulence (density or magnetic
field variations). This process should be present in the region close to the reconnection site (e.g., in the plasma reconnection outflows) where the density and the magnetic field vary strongly. 相似文献
12.
We revisit the flare that occurred on 13 January 1992, which is now universally termed the “Masuda flare”. The new analysis
is motivated not just by its uniqueness despite the increasing number of coronal observations in hard X-rays, but also by
the improvement of Yohkoh hard X-ray image processing, which was achieved after the intensive investigations on this celebrated event. Using an uncertainty
analysis, we show that the hard X-ray coronal source is located closer to the soft X-ray loop by about 5000 km (or 7 arcsec)
in the re-calibrated Hard X-ray Telescope (HXT) images than in the original ones. Specifically, the centroid of the M1-band
(23 – 33 keV) coronal source is above the maximum brightness of the Soft X-ray Telescope (SXT) loop by 5000±1000 km (9600
km in the original data) and above the apex of the SXT loop represented by the 30% brightness contour by 2000±1000 km (∼ 7000 km
in the original data). The change is obviously significant, because most coronal sources are above the thermal loop by less
than 6 arcsec. We suggest that this change may account for the discrepancy in the literature, i.e., the spectrum of the coronal emission was reported to be extremely hard below ∼ 20 keV in the pre-calibration investigations,
whereas it was reported to be considerably softer in the literature after the re-calibration done by Sato, Kosugi, and Makishima
(Pub. Astron. Soc. Japan
51, 127, 1999). Still, the coronal spectrum is flatter at lower energies than at higher energies, due to the lack of a similar, co-spatial
source in the L-band (14 – 23 keV), for which a convincing explanation is absent. 相似文献
13.
In the framework of ‘microscopic’ theory of black holes (J. Phys. Soc. Jpn. Suppl. B 70, 84, 2001; Astrophys. USSR 4, 659, 1996; 35, 335, 1991, 33, 143, 1990, 31, 345, 1989a; Astrophys. Space Sci. 1, 1992; Dokl. Akad. Nauk USSR 309, 97, 1989b), and references therein, we address the ‘pre-radiation time’ (PRT) of neutrinos from black holes, which implies the lapse
of time from black hole’s birth till radiation of an extremely high energy neutrinos. For post-PRT lifetime, the black hole
no longer holds as a region of spacetime that cannot communicate with the external universe. We study main features of spherical
accretion onto central BH and infer a mass accretion rate onto it, and, further, calculate the resulting PRT versus bolometric
luminosity due to accretion onto black hole. We estimate the PRTs of AGN black holes, with the well-determined masses and
bolometric luminosities, collected from the literature by Woo Jong-Hak and Urry (Astrophys. J. 579, 530, 2002) on which this paper is partially based. The simulations for the black holes of masses M
BH
≃(1.1⋅106
÷4.2⋅109) M
⊙ give the values of PRTs varying in the range of about T
BH
≃(4.3⋅105
÷5.6⋅1011) yr. The derived PRTs for the 60 AGN black holes are longer than the age of the universe (∼13.7 Gyr) favored today. At present,
some of remaining 174 BHs may radiate neutrinos. However, these results would be underestimated if the reservoir of gas for
accretion in the galaxy center is quite modest, and no obvious way to feed the BHs with substantial accretion. 相似文献
14.
Using nine years of solar wind plasma and magnetic field data from the Wind mission, we investigated the characteristics of both magnetic clouds (MCs) and magnetic cloud-like structures (MCLs) during
1995 – 2003. A MCL structure is an event that is identified by an automatic scheme (Lepping, Wu, and Berdichevsky, Ann. Geophys.
23, 2687, 2005) with the same criteria as for a MC, but it is not usually identifiable as a flux rope by using the MC (Burlaga et al., J. Geophys. Res.
86, 6673, 1981) fitting model developed by Lepping, Jones, and Burlaga (Geophys. Res. Lett.
95(11), 957, 1990). The average occurrence rate is 9.5 for MCs and 13.6 for MCLs per year for the overall period of interest, and there were
82 MCs and 122 MCLs identified during this period. The characteristics of MCs and MCL structures are as follows: (1) The average
duration, Δt, of MCs is 21.1 h, which is 40% longer than that for MCLs (Δt=15 h); (2) the average
(minimum B
z
found in MC/MCL measured in geocentric solar ecliptic coordinates) is −10.2 nT for MCs and −6 nT for MCLs; (3) the average
Dstmin (minimum Dst caused by MCs/MCLs) is −82 nT for MCs and −37 nT for MCLs; (4) the average solar wind velocity is 453 km s−1 for MCs and 413 km s−1 for MCLs; (5) the average thermal speed is 24.6 km s−1 for MCs and 27.7 km s−1 for MCLs; (6) the average magnetic field intensity is 12.7 nT for MCs and 9.8 nT for MCLs; (7) the average solar wind density
is 9.4 cm−3 for MCs and 6.3 cm−3 for MCLs; and (8) a MC is one of the most important interplanetary structures capable of causing severe geomagnetic storms.
The longer duration, more intense magnetic field and higher solar wind speed of MCs, compared to those properties of the MCLs,
are very likely the major reasons for MCs generally causing more severe geomagnetic storms than MCLs. But the fact that a
MC is an important interplanetary structure with respect to geomagnetic storms is not new (e.g., Zhang and Burlaga, J. Geophys. Res.
93, 2511, 1988; Bothmer, ESA SP-535, 419, 2003). 相似文献
15.
We performed a detailed analysis of 27 slow coronal mass ejections (CMEs) whose heights were measured in at least 30 coronagraphic
images and were characterized by a high quality index (≥4). Our primary aim was to study the radial evolution of these CMEs
and their properties in the range 2 – 30 solar radii. The instantaneous speeds of CMEs were calculated by using successive
height – time data pairs. The obtained speed – distance profiles [v(R)] are fitted by a power law v = a(R−b)
c
. The power-law indices are found to be in the ranges a=30 – 386, b=1.95 – 3.92, and c=0.03 – 0.79. The power-law exponent c is found to be larger for slower and narrower CMEs. With the exception of two events that had approximately constant velocity,
all events were accelerating. The majority of accelerating events shows a v(R) profile very similar to the solar-wind profile deduced by Sheeley et al. (Astrophys. J.
484, 472, 1997). This indicates that the dynamics of most slow CMEs are dominated by the solar wind drag. 相似文献
16.
G. Allen Gary 《Solar physics》2009,257(2):271-286
The minimum dissipative rate (MDR) method for deriving a coronal non-force-free magnetic field solution is partially evaluated.
These magnetic field solutions employ a combination of three linear (constant-α) force-free-field solutions with one being a potential field (i.e., α=0). The particular case of the solutions where the other two α’s are of equal magnitude but of opposite sign is examined. This is motivated by studying the SOLIS (Synoptic Optical Long-term
Investigation of the Sun (SOLIS), a National Solar Observatory facility) vector magnetograms of AR 10987, which show a global
α value consistent with an α=0 value as evaluated by (∇×B)
z
/B
z
over the region. Typical of the current state of the observing technology, there is no definitive twist for input into the
general MDR method. This suggests that the special α case, of two α’s with equal magnitudes and opposite signs, is appropriate given the data. Only for an extensively twisted active region
does a dominant, nonzero α normally emerge from a distribution of local values. For a special set of conditions, is it found that (i) the resulting
magnetic field is a vertically inflated magnetic field resulting from the electric currents being parallel to the photosphere,
similar to the results of Gary and Alexander (Solar Phys. 186:123, 1999), and (ii) for α≈(α
max /2), the Lorentz force per unit volume normalized by the square of the magnetic field is on the order of 1.4×10−10 cm−1. The Lorentz force (F
L) is a factor of ten higher than that of the magnetic force d(B
2/8π)/dz, a component of F
L. The calculated photospheric electric current densities are an order of magnitude smaller than the maximum observed in all
active regions. Hence both the Lorentz force density and the generated electric current density seem to be physically consistent
with possible solar dynamics. The results imply that the field could be inflated with an overpressure along the neutral line.
However, the implementation of this or any other extrapolation method using the electric current density as a lower boundary
condition must be done cautiously, with the current magnetography. 相似文献
17.
One goal of helioseismology is to determine the subsurface structure of sunspots. In order to do so, it is important to understand
first the near-surface effects of sunspots on solar waves, which are dominant. Here we construct simplified, cylindrically-symmetric
sunspot models that are designed to capture the magnetic and thermodynamics effects coming from about 500 km below the quiet-Sun
τ
5000=1 level to the lower chromosphere. We use a combination of existing semi-empirical models of sunspot thermodynamic structure
(density, temperature, pressure): the umbral model of Maltby et al. (1986, Astrophys. J. 306, 284) and the penumbral model of Ding and Fang (1989, Astron. Astrophys. 225, 204). The OPAL equation-of-state tables are used to derive the sound-speed profile. We smoothly merge the near-surface properties
to the quiet-Sun values about 1 Mm below the surface. The umbral and penumbral radii are free parameters. The magnetic field
is added to the thermodynamic structure, without requiring magnetostatic equilibrium. The vertical component of the magnetic
field is assumed to have a Gaussian horizontal profile, with a maximum surface field strength fixed by surface observations.
The full magnetic-field vector is solenoidal and determined by the on-axis vertical field, which, at the surface, is chosen
such that the field inclination is 45° at the umbral – penumbral boundary. We construct a particular sunspot model based on
SOHO/MDI observations of the sunspot in active region NOAA 9787. The helioseismic signature of the model sunspot is studied
using numerical simulations of the propagation of f, p
1, and p
2 wave packets. These simulations are compared against cross-covariances of the observed wave field. We find that the sunspot
model gives a helioseismic signature that is similar to the observations. 相似文献
18.
Yu Liu 《Solar physics》2008,249(1):75-84
Liu et al. (Astrophys. J.
628, 1056, 2005a) described one surge – coronal mass ejection (CME) event showing a close relationship between solar chromospheric surge ejection
and CME that had not been noted before. In this work, large Hα surges (>72 Mm, or 100 arcsec) are studied. Eight of these
were associated with CMEs. According to their distinct morphological features, Hα surges can be classified into three types:
jetlike, diffuse, and closed loop. It was found that all of the jetlike surges were associated with jetlike CMEs (with angular
widths ≤30 degrees); the diffuse surges were all associated with wide-angle CMEs (e.g., halo); the closed-loop surges were not associated with CMEs. The exclusive relation between Hα surges and CMEs indicates
difference in magnetic field configurations. The jetlike surges and related narrow CMEs propagate along coronal fields that
are originally open. The unusual transverse mass motions in the diffuse surges are suggested to be due to magnetic reconnections
in the corona that produce wide-angle CMEs. For the closed-loop surges, their paths are just outlining stable closed loops
close to the solar surface. Thus no CMEs are associated with them. 相似文献
19.
Using RHESSI and some auxiliary observations we examine possible connections between the spatial and temporal structure of
nonthermal hard X-ray (HXR) emission sources from the two-ribbon flares of 29 May 2003 and 19 January 2005. In each of these
events quasi-periodic pulsations (QPP) with time period of 1 – 3 minutes are evident in both hard X rays and microwaves. The
sources of nonthermal HXR emission are situated mainly at the footpoints of the flare arcade loops observed by TRACE and the
SOHO/EIT instrument in the EUV range. At least one of the sources moves systematically during and after the QPP phase in each
flare. The sources move predominantly parallel to the magnetic inversion line during the 29 May flare and along flare ribbons
during the QPP phase of both flares. By contrast, the sources start to show movement perpendicular to the flare ribbons with
velocity comparable to that along the ribbons’ movement after the QPP phase. The sources of each pulse are localized in distinct
parts of the ribbon during the QPP phase. The measured velocity of the sources and the estimated energy release rate do not
correlate well with the flux of the HXR emission calculated from these sources. The sources of microwaves and thermal HXRs
are situated near the apex of the flare loop arcade and are not stationary either. Almost all of the QPP as well as some pulses
of nonthermal HXR emission during the post-QPP phase reveal soft – hard – soft spectral behavior, indicating separate acts
of electron acceleration and injection. In our opinion at least two different flare scenarios based on the Nakariakov et al. (2006, Astron. Astrophys.
452, 343) model and on the idea of current-carrying loop coalescence are suitable for interpreting the observations. However,
it is currently not possible to choose between them owing to observational limitations. 相似文献
20.
High-resolution Hα filtergrams (0.2″) obtained with the Swedish 1-m Solar Telescope resolve numerous very thin, thread-like
structures in solar filaments. The threads are believed to represent thin magnetic flux tubes that must be longer than the
observable threads. We report on evidence for small-amplitude (1 – 2 km s−1) waves propagating along a number of threads with an average phase velocity of 12 km s−1 and a wavelength of 4″. The oscillatory period of individual threads vary from 3 to 9 minutes. Temporal variation of the
Doppler velocities averaged over a small area containing a number of individual threads shows a short-period (3.6 minutes)
wave pattern. These short-period oscillations could possibly represent fast modes in accordance with numerical fibril models
proposed by Díaz et al. (Astron. Astrophys.
379, 1083, 2001). In some cases, it is clear that the propagating waves are moving in the same direction as the mass flows. 相似文献