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1.
It is generally believed that gradual solar energetic particles (SEPs) are accelerated by shocks associated with coronal mass
ejections (CMEs). Using an ice-cream cone model, the radial speed and angular width of 95 CMEs associated with SEP events
during 1998 – 2002 are calculated from SOHO/LASCO observations. Then, we investigate the relationships between the kinematic
properties of these CMEs and the characteristic times of the intensity-time profile of their accompanied SEP events observed
at 1 AU. These characteristic times of SEP are i) the onset time from the accompanying CME eruption at the Sun to the SEP arrival at 1 AU, ii) the rise time from the SEP onset to the time when the SEP intensity is one-half of peak intensity, and iii) the duration over which the SEP intensity is within a factor of two of the peak intensity. It is found that the onset time
has neither significant correlation with the radial speed nor with the angular width of the accompanying CME. For events that
are poorly connected to the Earth, the SEP rise time and duration have no significant correlation with the radial speed and
angular width of the associated CMEs. However, for events that are magnetically well connected to the Earth, the SEP rise
time and duration have significantly positive correlations with the radial speed and angular width of the associated CMEs.
This indicates that a CME event with wider angular width and higher speed may more easily drive a strong and wide shock near
to the Earth-connected interplanetary magnetic field lines, may trap and accelerate particles for a longer time, and may lead
to longer rise time and duration of the ensuing SEP event. 相似文献
2.
The Reuven Ramaty High Energy Spectroscopic Imager (RHESSI) X-ray data base (February 2002 – May 2006) has been searched to find solar flares with weak thermal components and
flat photon spectra. Using a regularized inversion technique, we determine the mean electron flux distribution from count
spectra for a selection of events with flat photon spectra in the 15 – 20 keV energy range. Such spectral behavior is expected
for photon spectra either affected by photospheric albedo or produced by electron spectra with an absence of electrons in
a given energy range (e.g., a low-energy cutoff in the mean electron spectra of nonthemal particles). We have found 18 cases that exhibit a statistically
significant local minimum (a dip) in the range of 13 – 19 keV. The positions and spectral indices of events with low-energy
cutoff indicate that such features are likely to be the result of photospheric albedo. It is shown that if the isotropic albedo
correction is applied, all low-energy cutoffs in the mean electron spectrum are removed, and hence the low-energy cutoffs
in the mean electron spectrum of solar flares above ∼ 12 keV cannot be viewed as real features. If low-energy cutoffs exist
in the mean electron spectra, their energies should be less than ∼ 12 keV. 相似文献
3.
A new index, the cumulative difference of sunspot activity in the northern and southern hemispheres, respectively, is proposed
to describe the long-term behavior of the North – South asymmetry of sunspot activity and to show the balance (or bias) of
sunspot activity in the two solar hemispheres on a long-term scale. Sunspot groups and sunspot areas from June 1874 to January
2007 are used to show the advantage of the index. The index clearly shows a long-term characteristic time scale of about 12
cycles in the North – South asymmetry of sunspot activity. Sunspot activity is found to dominate in the southern hemisphere
in cycle 23, and in cycle 24 it is predicted to dominate still in the southern hemisphere. A comparison of the new index with
other similar indexes is also given. 相似文献
4.
Quasi-periodic pulsations (QPP) of microwave emission generated in single flaring loops observed with the Nobeyama Radioheliograph (NoRH) and Nobeyama Radio Polarimeters (NoRP) are studied. Specific features of the time profiles, i.e. the visible presence or absence of QPPs, are not accounted for in the selection. The time evolution of the periods of the
QPPs is examined using wavelet and correlation analyses. In ten out of twelve considered events, at least one or more significant
spectral components with periods from 5 – 60 s have been found. The quality of the oscillations is rather low: Q=π
N, where N is the number of cycles, mostly varies in the range 12 to 40, with an average of 25. We suggest that the detected QPPs can
be classified into four types: i) those with stable mean periods (e.g. of 15 – 20 s or 8 – 9 s, the prevailing type); ii) those with spectral drift to shorter periods (mostly in the rise phase of the microwave emission); iii) those with drift to longer periods (mostly in the decay phase); iv) those with multiple periods showing an X-shaped drift (e.g. in the range from 20 – 40 s in the rise phase). 相似文献
5.
The north – south (N – S) asymmetry of solar activity is investigated by using the data on coronal green-line brightness and
total number and total area of sunspots over the period of 1939 – 2001. Typical time variations of the N – S asymmetry are
found to be consonant in these indices. Quasi-biennial oscillations (QBO) of solar activity are well recognizable in the N – S
asymmetry of the examined indices. Moreover, the QBO are much better manifested in the N – S asymmetry of the individual indices
than in the original (N plus S) indices. The time variations of relative QBO power are synchronous for the N – S asymmetry
of various solar activity indices whereas such a synchronization is weaker for the indices themselves. It is revealed that
the relative QBO power found in the N – S asymmetry of the studied indices has a negative correlation with the value of the
N – S asymmetry itself. The findings indicate that the N – S asymmetry should be regarded as a fundamental phenomenon of solar
activity similarly manifested in different activity indices. These findings should be taken into account when any dynamo theory
of solar activity is constructed. 相似文献
6.
A detailed analysis of characteristics of coronal mass ejections and flares associated with deca-hectometer wavelength type-II radio bursts (DH-CMEs and DH-flares) observed in the period 1997–2008 is presented. A sample of 62 limb events is divided into two populations known as after-flare CMEs (AF-CMEs) and before-flare CMEs (BF-CMEs) based on the relative timing of the flare and CME onsets. On average, AF-CMEs (1589 km s−1) have more speed than the BF-CMEs (1226 km s−1) and the difference between mean values are highly significant (P∼2%). The average CME nose height at the time of type-II start is at larger distance for AF-CMEs than the BF-CMEs (4.89 and 3.84 R o, respectively). We found a good anti-correlation for accelerating (R a=−0.89) and decelerating (R d=−0.78) AF-CMEs. In the case of decelerating BF-CMEs, the correlation seems to be similar to that for decelerating AF-CMEs (R d=−0.83). The number of decelerating AF-CMEs is 51% only; where as, the number of decelerating BF-CMEs is 83%. The flares associated with BF-CMEs have shorter rise and decay times than flares related to AF-CMEs. We found statistically significant differences between the two sets of associated DH-type-II bursts characteristics: starting frequency (P∼4%), drift rate (P∼1%), and ending frequency (P∼6%). The delay time analysis of DH-type-II start and flare onset times shows that the time lags are longer in AF-CME events than in BF-CME events (P≪1%). From the above results, the AF-CMEs which are associated with DH-type-II bursts are found to be more energetic, associated with long duration flares and DH-type-IIs of lower ending frequencies. 相似文献
7.
According to research results from solar-dynamo models, the northern and southern hemispheres may evolve separately throughout
the solar cycle. The observed phase lag between the northern and southern hemispheres provides information regarding how strongly
the hemispheres are coupled. Using hemispheric sunspot-area and sunspot-number data from Cycles 12 – 23, we determine how
out of phase the separate hemispheres are during the rising, maximum, and declining period of each solar cycle. Hemispheric
phase differences range from 0 – 11, 0 – 14, and 2 – 19 months for the rising, maximum, and declining periods, respectively.
The phases appear randomly distributed between zero months (in phase) and half of the rise (or decline) time of the solar
cycle. An analysis of the sunspot cycle double peak, or Gnevyshev gap, is conducted to determine if the double-peak is caused
by the averaging of two hemispheres that are out of phase. We confirm previous findings that the Gnevyshev gap is a phenomenon
that occurs in the separate hemispheres and is not due to a superposition of sunspot indices from hemispheres slightly out
of phase. Cross hemispheric coupling could be strongest at solar minimum, when there are large quantities of magnetic flux
at the Equator. We search for a correlation between the hemispheric phase difference near the end of the solar cycle and the
length of solar-cycle minimum, but found none. Because magnetic flux diffusion across the Equator is a mechanism by which
the hemispheres couple, we measured the magnetic flux crossing the Equator by examining Kitt Peak Vacuum Telescope and SOLIS
magnetograms for Solar Cycles 21 – 23. We find, on average, a surplus of northern hemisphere magnetic flux crossing during
the mid-declining phase of each solar cycle. However, we find no correlation between magnitude of magnetic flux crossing the
Equator, length of solar minima, and phase lag between the hemispheres. 相似文献
8.
Observations indicate that in plage areas (i.e. in active regions outside sunspots) acoustic waves travel faster than in the quiet Sun, leading to shortened travel times
and higher p-mode frequencies. Coupled with the 11-year variation of solar activity, this may also explain the solar cycle variation of
oscillation frequencies. While it is clear that the ultimate cause of any difference between the quiet Sun and plage is the
presence of magnetic fields of order 100 G in the latter, the mechanism by which the magnetic field exerts its influence has
not yet been conclusively identified. One possible such mechanism is suggested by the observation that granular motions in
plage areas tend to be slightly “abnormal”, dampened compared to the quiet Sun.
In this paper we consider the effect that abnormal granulation observed in active regions should have on the propagation of
acoustic waves. Any such effect is found to be limited to a shallow surface layer where sound waves propagate nearly vertically.
The magnetically suppressed turbulence implies higher sound speeds, leading to shorter travel times. This time shift Δ
τ is independent of the travel distance, while it shows a characteristic dependence on the assumed plage field strength. As
a consequence of the variation of the acoustic cutoff with height, Δ
τ is expected to be significantly higher for higher frequency waves within the observed regime of 3 – 5 mHz. The lower group
velocity near the upper reflection point further leads to an increased envelope time shift, as compared to the phase shift.
p-mode frequencies in plage areas are increased by a corresponding amount, Δ
ν/ν=ν
Δ
τ. These characteristics of the time and frequency shifts are in accordance with observations. The calculated overall amplitudes
of the time and frequency shifts are comparable to, but still significantly less than (by a factor of 2 to 5), those suggested
by measurements. 相似文献
9.
V. A. Sheminova 《Solar physics》2009,254(1):29-50
The properties of solar magnetic fields on scales less than the spatial resolution of solar telescopes are studied. A synthetic
infrared spectropolarimetric diagnostic based on a 2D MHD simulation of magnetoconvection is used for this. Analyzed are two
time sequences of snapshots that likely represent two regions of the network fields with their immediate surroundings on the
solar surface with unsigned magnetic flux densities of 300 and 140 G. In the first region from the probability density functions
of the magnetic field strength it is found that the most probable field strength at log τ
5=0 is equal to 250 G. Weak fields (B<500 G) occupy about 70% of the surface, whereas stronger fields (B>1000 G) occupy only 9.7% of the surface. The magnetic flux is −28 G and its imbalance is −0.04. In the second region, these
parameters are correspondingly equal to 150 G, 93.3%, 0.3%, −40 G, and −0.10. The distribution of line-of-sight velocities
on the surface of log τ
5=−1 is estimated. The mean velocity is equal to 0.4 km s−1 in the first simulated region. The average velocity in the granules is −1.2 km s−1 and in the intergranules it is 2.5 km s−1. In the second region, the corresponding values of the mean velocities are equal to 0, −1.8, and 1.5 km s−1. In addition the asymmetry of synthetic Stokes V profiles of the Fe i 1564.8 nm line is analyzed. The mean values of the amplitude and area asymmetry do not exceed 1%. The spatially smoothed
amplitude asymmetry is increased to 10% whereas the area asymmetry is only slightly varied. 相似文献
10.
P. M. S. Namboodiri 《Celestial Mechanics and Dynamical Astronomy》2000,76(1):69-77
Oscillations in galaxies have been investigated by numerical simulations. The various models used have density distributions
corresponding to that of polytrope of index n in the range 0 ≤ n ≤ 4 and their evolution has been followed for more than 70 crossing times. The kinetic energy shows regular and smooth oscillations
for models with n = 0, 1 and 2 whereas in other models it shows noisy oscillation. The oscillation in kinetic energy is observed to have a
period of 3 crossing time irrespective of the density and size of the galaxy. The amplitude of oscillation is seen to decrease
as the central density of the galaxy increases.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
C. O. Lee J. G. Luhmann D. Odstrcil P. J. MacNeice I. de Pater P. Riley C. N. Arge 《Solar physics》2009,254(1):155-183
We present results of solar-wind parameters generated by 3D MHD models. The ENLIL inner-heliosphere solar-wind model together
with the MAS or Wang – Sheeley – Arge (WSA) coronal models, describe the steady solar-wind stream structure and its origins
in the solar corona. The MAS/ENLIL and WSA/ENLIL models have been tuned to provide a simulation of plasma moments as well
as interplanetary magnetic-field magnitude and polarity in the absence of disturbances from coronal transients. To investigate
how well the models describe the ambient solar wind structure from the Sun out to 1 AU, the model results are compared to
solar-wind measurements from the ACE spacecraft. We find that there is an overall agreement between the observations and the
model results for the general large-scale solar-wind structures and trends, such as the timing of the high-density structures
and the low- and high-speed winds, as well as the magnetic sector structures. The time period of our study is the declining
phase of Solar Cycle 23 when the solar activity involves well-defined stream structure, which is ideal for testing a quasi-steady-state
solar-wind model. 相似文献
12.
We study the space – time distributions of intensity fluctuations in 2 – 3 hour sequences of multi-spectral, high-resolution,
high-cadence, broad-band filtergram images of the Sun made by the SOT – FG system aboard the Hinode spacecraft. In the frequency
range 5.5<f<8.0 mHz both G-band and Ca ii H-line oscillations are suppressed in the presence of magnetic fields, but the suppression disappears for f>10 mHz. By looking at G-band frequencies above 10 mHz we find that the oscillatory power, both at these frequencies and at
lower frequencies, lies in a mesh pattern with cell scale 2 – 3 Mm, clearly larger than normal granulation, and with correlation
times on the order of hours. The mesh pattern lies in the dark lanes between stable cells found in time-integrated G-band
intensity images. It also underlies part of the bright pattern in time-integrated H-line emission. This discovery may reflect
dynamical constraints on the sizes of rising granular convection cells together with the turbulence created in strong intercellular
downflows. 相似文献
13.
We investigate the properties of acoustic events (AEs), defined as spatially concentrated and short duration energy flux,
in the quiet Sun, using observations of a 2D field of view (FOV) with high spatial and temporal resolution provided by the
Solar Optical Telescope (SOT) onboard Hinode. Line profiles of Fe i 557.6 nm were recorded by the Narrow-band Filter Imager (NFI) on a 82″×82″ FOV during 75 min with a time step of 28.75 s
and 0.08″ pixel size. Vertical velocities were computed at three atmospheric levels (80, 130, and 180 km) using the bisector
technique, allowing the determination of energy flux to be made in the range 3 – 10 mHz using two complementary methods (Hilbert
transform and Fourier power spectrum). Horizontal velocities were computed using local correlation tracking (LCT) of continuum
intensities providing divergences. We found that the net energy flux is upward. In the range 3 – 10 mHz, a full FOV space
and time averaged flux of 2700 W m−2 (lower layer 80 – 130 km) and 2000 W m−2 (upper layer 130 – 180 km) is concentrated in less than 1 % of the solar surface in the form of narrow (0.3″) AE. Their total
duration (including rise and decay) is of the order of 103 s. Inside each AE, the mean flux is 1.6×105 W m−2 (lower layer) and 1.2×105 W m−2 (upper). Each event carries an average energy (flux integrated over space and time) of 2.5×1019 J (lower layer) to 1.9×1019 J (upper). More than 106 events could exist permanently on the Sun, with a birth and decay rate of 3500 s−1. Most events occur in intergranular lanes, downward velocity regions, and areas of converging motions. 相似文献
14.
J. Javaraiah 《Solar physics》2011,270(2):463-483
Using the combined Greenwich (1874 – 1976) and Solar Optical Observatories Network (1977 – 2009) data on sunspot groups, we
study the long-term variations in the mean daily rates of growth and decay of sunspot groups. We find that the minimum and
the maximum values of the annually averaged daily mean growth rates are ≈ 52% day−1 and ≈ 183% day−1, respectively, whereas the corresponding values of the annually averaged daily mean decay rates are ≈ 21% day−1 and ≈ 44% day−1, respectively. The average value (over the period 1874 – 2009) of the growth rate is about 70% more than that of the decay
rate. The growth and the decay rates vary by about 35% and 13%, respectively, on a 60-year time scale. From the beginning
of Cycle 23 the growth rate is substantially decreased and near the end (2007 – 2008) the growth rate is lowest in the past
about 100 years. In the extended part of the declining phase of this cycle, the decay rate steeply increased and it is largest
in the beginning of the current Cycle 24. These unusual properties of the growth and the decay rates during Cycle 23 may be
related to cause of the very long declining phase of this cycle with the unusually deep and prolonged current minimum. A ≈ 11-year
periodicity in the growth and the decay rates is found to be highly latitude and time dependent and seems to exist mainly
in the 0° – 10° latitude interval of the southern hemisphere. The strength of the known approximate 33 – 44-year modulation
in the solar activity seems to be related to the north-south asymmetry in the growth rate. Decreasing and increasing trends
in the growth and the decay rates indicate that the next 2 – 3 solar cycles will be relatively weak. 相似文献
15.
We study the zonal flow in solar subsurface layers, analyzing about six years of GONG++ high-resolution Doppler data with
ring-diagram analysis. We focus on the variation of zonal flow with magnetic activity over a range of depths from the surface
to about 16 Mm. There is a positive correlation between unsigned magnetic flux and zonal flow at most depths. We calculate
the average zonal flow for a quiet- and an active-region subset defined as dense-pack locations with an unsigned magnetic
flux less than 3.4 G and locations with greater than 65.0 G, respectively. The average zonal flow of active regions is about
4 m s−1 larger than the average flow of quiet regions. This difference increases slightly with increasing depth, which might be explained
by a nonradial inclination of the flux tubes or a different extent in depth of different magnetic features. The difference
shows no apparent pattern in time and latitude, which makes it unlikely that it is simply a manifestation of the torsional-oscillation
pattern. As a byproduct, we find that the size of the North – South asymmetry of the rotation rate decreases during the same
epoch. 相似文献
16.
We study the sensitivity of wave travel times to steady and spatially homogeneous horizontal flows added to a realistic simulation
of the solar convection performed by Robert F. Stein, Ake Nordlund, Dali Georgobiani, and David Benson. Three commonly used
definitions of travel times are compared. We show that the relationship between travel-time difference and flow amplitude
exhibits a non-linearity depending on the travel distance, the travel-time definition considered, and the details of the time – distance
analysis (in particular, the impact of the phase-speed filter width). For times measured using a Gabor wavelet fit, the travel-time
differences become nonlinear in the flow strength for flows of about 300 m s−1, and this non-linearity reaches almost 60% at 1200 m s−1 (relative difference between actual travel time and expected time for a linear behavior). We show that for travel distances
greater than about 17 Mm, the ray approximation predicts the sensitivity of travel-time shifts to uniform flows. For smaller
distances, the ray approximation can be inaccurate by more than a factor of three. 相似文献
17.
Prediction of Solar Cycle Maximum Using Solar Cycle Lengths 总被引：1，自引：0，他引：1
R. P. Kane 《Solar physics》2008,248(1):203-209
If the rise time RT, fall time FT, and total time TT (i.e., RT+FT) of a solar cycle are compared against the maximum amplitude Rz(max ) for the following cycle, then only the association between TT and Rz(max ) is inferred to be well anticorrelated, inferring that the larger (smaller) the value of Rz(max ) for the following cycle, the shorter (longer) the TT of the preceding cycle. Although the inferred correlation (−0.68)
is statistically significant, the inferred standard error of estimate is quite large, so predictions using the inferred correlation
are not very precise. Removal of cycle pairs 15/16, 19/20, and 20/21 (statistical outliers) yields a regression that is highly
statistically significant (−0.85) and reduces the standard error of estimate by 18%. On the basis of the adjusted regression
and presuming TT=140 months for cycle 23, the present ongoing cycle, cycle 24’s 90% prediction interval for Rz(max ) is estimated to be about 94±44, inferring only a 5% probability that its Rz(max ) will be larger than about 140, unless of course cycle pair 23/24 is a statistical outlier. 相似文献
18.
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
19.
Jiangtao Su Yu Liu Jihong Liu Xinjie Mao Hongqi Zhang Hui Li Xiaofan Wang Wenbin Xie 《Solar physics》2008,252(1):55-71
Zhao and Kosovichev (Astrophys. J.
591, 446, 2003) found two opposite sub-photospheric vortical flows in the depth range of 0 – 12 Mm around a fast rotating sunspot. So far
there is no theoretical model explaining such flow motions. In this paper, we try to explain this phenomenon from the point
of view of magnetic flux tubes interacting with large-scale vortical motions of plasma. In the deeper zone under the photosphere,
the magnetic force may be less than the nonmagnetic force of plasma. The vortical flow located there twists the flux tube
and magnetic free energy is built up in the tube. In the shallower zone under the photosphere, the magnetic force may be greater
than the nonmagnetic force. Thus, part of the stored magnetic free energy is released to drive the plasma to rotate in two
opposite directions, e.g., in the depth ranges of 0 – 3(5) and 9 – 12 Mm. In addition, we also define a vector of nonpotential magnetic stress τ, which can be related to flare occurrence. It is calculated for the active region NOAA 10930 on 11 December 2006. We find
that: i) the integral of its line-of-sight (LOS) stress successively increases around the magnetic neutral line (MNL) prior to and
during the flare and decreases to a minimum after the flare; ii) the integral of its transverse stress exceeds the integral of its LOS component by one order of magnitude over the whole
field of view; iii) the transverse stress first points toward the MNL, then along it, and finally it points away from it. We need other data
to verify whether or not the magnetic energy is transported in the horizontal direction to the neutral line, and then partly
changes into the energy in LOS direction before and during the flare. 相似文献
20.
We report on the detailed analysis of i) differences between the properties of type IIs with various starting frequencies (high: ≥100 MHz; low: ≤50 MHz; mid: 50 MHz
≤f≤ 100 MHz) and ii) the properties of CMEs and flares associated with them. For this study, we considered a sample of type II radio bursts observed
by Culgoora radio spectrograph from January 1998 to December 2000. The X-ray flares and CMEs associated with these events
are identified using GOES and SOHO/LASCO data. The secondary aim is to study the frequency dependence on other properties
of type IIs, flares, and CMEs. We found that the type IIs with high starting frequencies have larger drift rate, relative
drift rate, and shock speed than the type IIs with low starting frequencies. The flares associated with high frequency type
IIs are of impulsive in nature with shorter rise time, duration and delay between the flare start and type II start times
than the low frequency type IIs. There is a distinct power – law relationship between the flare parameters and the starting
frequencies of type II bursts, whereas the trend in the CME parameters shows low correlation. While the mean speed of CMEs
is larger for the mid-frequency group, it is nearly the same for the high and low frequency groups. On the other hand, the
percentage of CME association (90%) is larger for low frequency type IIs than for the high frequency type IIs (75%). 相似文献