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1.
We applied special data-processing algorithms to the study of long-period oscillations of the magnetic-field strength and
the line-of-sight velocity in sunspots. The oscillations were investigated with two independent groups of data. First, we
used an eight-hour-long series of solar spectrograms, obtained with the solar telescope at the Pulkovo Observatory. We simultaneously
measured Doppler shifts of six spectral lines, formed at different heights in the atmosphere. Second, we had a long time series
of full-disk magnetograms (10 – 34 hour) from SOHO/MDI for the line-of-sight magnetic-field component. Both ground- and space-based
observations revealed long-period modes of oscillations (40 – 45, 60 – 80, and 160 – 180 minutes) in the power spectrum of
the sunspots and surrounding magnetic structures. With the SOHO/MDI data, one can study the longer periodicities. We obtained
two new significant periods (> 3σ) in the power spectra of sunspots: around 250 and 480 minutes. The power of the oscillations in the lower frequencies is
always higher than in the higher ones. The amplitude of the long-period magnetic-field modes shows magnitudes of about 200 – 250 G.
The amplitude of the line-of-sight velocity periodicities is about 60 – 110 m s−1. The absence of low-frequency oscillations in the telluric line proves their solar nature. Moreover, the absence of low-frequency
oscillations of the line-of-sight velocity in the quiet photosphere (free of magnetic elements) proves their direct connection
to magnetic structures. Long-period modes of oscillation observed in magnetic elements surrounding the sunspot are spread
over the meso-granulation scales (10″ – 12″), while the sunspot itself oscillates as a whole. The amplitude of the long-period
mode of the line-of-sight velocity in a sunspot decreases rapidly with height: these oscillations are clearly visible in the
spectral lines originating at heights of approximately 200 km and fade away in lines originating at 500 km. We found a new
interesting property: the low-frequency oscillations of a sunspot are strongly reduced when there is a steady temporal trend
(strengthening or weakening) of the sunspot’s magnetic field. Another important result is that the frequency of long-period
oscillations evidently depends on the sunspot’s magnetic-field strength. 相似文献
2.
Qixiu Li 《Solar physics》2008,249(1):135-145
The counts of the monthly averaged polar faculae, from observations of the National Astronomical Observatory of Japan (NAOJ),
are examined by using linear and nonlinear approaches to find the periodicity characteristics of the polar faculae in the
northern and southern hemispheres and the phase relationship between them. Both the cross-wavelet transform (XWT) and wavelet
coherence (WTC) indicate the prominent period with 95% confidence level, namely the Schwabe cycle of about 11 years. The Schwabe
cycle is in phase in the two hemispheres. Within the 11-year frequency band, there is a small phase difference during the
period of 1966 – 1975 when the activity of polar faculae in the northern hemisphere slightly leads the one in the southern
hemisphere. A cross-recurrence plot analysis and the line of synchronization (LOS) extracted from the cross-recurrence plot
show further the phase difference between the two hemispheres. The LOS deviates significantly from the main diagonal during
the period of 1965 – 1970 and LOS >0, showing that the activity of polar faculae in the northern hemisphere leads in phase,
which is in accordance with XWT and WTC analyses. Moreover, asynchronization is highest (about 30 months) during this period. 相似文献
3.
In our recent paper (Jakimiec and Tomczak, Solar Physics
261, 233, 2010) we investigated quasi-periodic oscillations of hard X-rays during the impulsive phase of solar flares. We have come to the
conclusion that they are caused by magnetosonic oscillations of magnetic traps within the volume of hard-X-ray (HXR) loop-top
sources. In the present paper we investigate four flares that show clear quasi-periodic sequences of the HXR pulses. We also
describe our phenomenological model of oscillating magnetic traps to show that it can explain the observed properties of the
HXR oscillations. The main results are the following: i) Low-amplitude quasi-periodic oscillations occur before the impulsive
phase of some flares. ii) The quasi-periodicity of the oscillations can change in some flares. We interpret this as being
due to changes of the length of oscillating magnetic traps. iii) During the impulsive phase a significant part of the energy
of accelerated (non-thermal) electrons is deposited within a HXR loop-top source. iv) The quick development of the impulsive
phase is due to feedback between the pressure pulses by accelerated electrons and the amplitude of the magnetic-trap oscillation.
v) The electron number density and magnetic field strength values obtained for the HXR loop-top sources in several flares
fall within the limits of N≈(2 – 15)×1010 cm−3, B≈(45 – 130) gauss. These results show that the HXR quasi-periodic oscillations contain important information about the energy
release in solar flares. 相似文献
4.
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
5.
In the present study, the short-term periodicities in the daily data of the sunspot numbers and areas are investigated separately
for the full disk, northern, and southern hemispheres during Solar Cycle 23 for a time interval from 1 January 2003 to 30
November 2007 corresponding to the descending and minimum phase of the cycle. The wavelet power spectrum technique exhibited
a number of quasi-periodic oscillations in all the datasets. In the high frequency range, we find a prominent period of 22 – 35
days in both sunspot indicators. Other quasi-periods in the range of 40 – 60, 70 – 90, 110 – 130, 140 – 160, and 220 – 240
days are detected in the sunspot number time series in different hemispheres at different time intervals. In the sunspot area
data, quasi-periods in the range of 50 – 80, 90 – 110, 115 – 130, 140 – 155, 160 – 190, and about 230 days were noted in different
hemispheres within the time period of analysis. The present investigation shows that the well-known “Rieger periodicity” of
150 – 160 days reappears during the descending phase of Solar Cycle 23, but this is prominent mainly in the southern part
of the Sun. Possible explanations of these observed periodicities are delivered on the basis of earlier results detected in
photospheric magnetic field time series (Knaack, Stenflo, and Berdyugina in Astron. Astrophys.
438, 1067, 2005) and solar r-mode oscillations. 相似文献
6.
A. Anđić 《Solar physics》2007,243(2):131-141
High-frequency velocity oscillations were observed in the spectral lines Fe i 543.45 nm and 543.29 nm, by using 2D spectroscopy with a Fabry – Perot and speckle reconstruction, at the Vacuum Tower Telescope
in Tenerife. We investigate the radial component of waves with frequencies in the range 8 – 22 mHz in the internetwork, network,
and a pore. We find that the occurrence of waves does not show any location preference and that they are equally distributed
over downflows and upflows, regardless of the activity of the observed area in the line of Fe i 543.45 nm. The waves observed in the lower formed line of Fe i 543.29 nm seem to appear preferentially over downflows. 相似文献
7.
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
8.
R. Sahai K. Young N. Patel C. Sánchez Contreras M. Morris 《Astrophysics and Space Science》2008,313(1-3):241-244
Using the Submillimeter Array (SMA), we have obtained high angular-resolution (∼1″) interferometric maps of the submillimeter
(0.88 mm) continuum and CO J=3–2 line from IRAS 22036+5306 (I 22036), a bipolar pre-planetary nebula (PPN) with knotty jets discovered in our HST SNAPshot
survey of young PPNe. In addition, we have obtained supporting lower-resolution (∼10″) 2.6 mm continuum and CO, 13CO J=1–0 observations with the Owens Valley Radio Observatory (OVRO) interferometer. We find an unresolved source of submillimeter
(and millimeter-wave) continuum emission in I 22036, implying a very substantial mass (0.02–0.04M
⊙) of large (i.e., radius ≳1 mm), cold (≲50 K) dust grains associated with I 22036’s toroidal waist. The CO J=3–2 observations show the presence of a very fast (∼220 km s−1), highly collimated, massive (0.03M
⊙) bipolar outflow with a very large scalar momentum (about 1039 g cm s−1), and the characteristic spatio-kinematic structure of bow-shocks at the tips of this outflow. The fast outflow in I 22036,
as in most PPNe, cannot be driven by radiation pressure. The large mass of the torus suggests that it has most likely resulted
from common-envelope evolution in a binary, however it remains to be seen whether or not the time-scales required for the
growth of grains to millimeter sizes in the torus are commensurate with such a formation scenario. The presence of the torus
should facilitate the formation of the accretion disk needed to launch the jet. We also find that the 13C/12C ratio in I 22036 is very high (0.16), close to the maximum value achieved in equilibrium CNO-nucleosynthesis (0.33). The
combination of the high circumstellar mass (i.e., in the torus and an extended dust shell inferred from ISO far-infrared spectra)
and the high 13C/12C ratio in I 22036 provides strong support for this object having evolved from a massive (≳4M
⊙) progenitor in which hot-bottom-burning has occurred. 相似文献
9.
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
10.
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
11.
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
12.
C. Bouratzis P. Preka-Papadema A. Hillaris P. Tsitsipis A. Kontogeorgos V. G. Kurt X. Moussas 《Solar physics》2010,267(2):343-359
We present a multi-frequency and multi-instrument study of the 20 January 2005 event. We focus mainly on the complex radio
signatures and their association with the active phenomena taking place: flares, CMEs, particle acceleration, and magnetic
restructuring. As a variety of energetic-particle accelerators and sources of radio bursts are present, in the flare – ejecta
combination, we investigate their relative importance in the progress of this event. The dynamic spectra of ARTEMIS-IV – Wind/Waves – HiRAS, with 2000 MHz – 20 kHz frequency coverage, were used to track the evolution of the event from the low corona to
the interplanetary space; these were supplemented with SXR, HXR, and γ-ray recordings. The observations were compared with the expected radio signatures and energetic-particle populations envisaged
by the Standard Flare – CME model and the reconnection outflow termination shock model. A proper combination of these mechanisms seems to provide an adequate model for the interpretation of the observational
data. 相似文献
13.
Rajmal Jain Arun Kumar Awasthi Arvind Singh Rajpurohit Markus J. Aschwanden 《Solar physics》2011,270(1):137-149
We report solar flare plasma to be multi-thermal in nature based on the theoretical model and study of the energy-dependent
timing of thermal emission in ten M-class flares. We employ high-resolution X-ray spectra observed by the Si detector of the
“Solar X-ray Spectrometer” (SOXS). The SOXS onboard the Indian GSAT-2 spacecraft was launched by the GSLV-D2 rocket on 8 May
2003. Firstly we model the spectral evolution of the X-ray line and continuum emission flux F(ε) from the flare by integrating a series of isothermal plasma flux. We find that the multi-temperature integrated flux F(ε) is a power-law function of ε with a spectral index (γ)≈−4.65. Next, based on spectral-temporal evolution of the flares we find that the emission in the energy range E=4 – 15 keV is dominated by temperatures of T=12 – 50 MK, while the multi-thermal power-law DEM index (δ) varies in the range of −4.4 and −5.7. The temporal evolution of the X-ray flux F(ε,t) assuming a multi-temperature plasma governed by thermal conduction cooling reveals that the temperature-dependent cooling
time varies between 296 and 4640 s and the electron density (n
e) varies in the range of n
e=(1.77 – 29.3)×1010 cm−3. Employing temporal evolution technique in the current study as an alternative method for separating thermal from nonthermal
components in the energy spectra, we measure the break-energy point, ranging between 14 and 21±1.0 keV. 相似文献
14.
In the present investigation we measure the differential rotation of strong magnetic flux during solar cycles 21 – 23 with
the method of wavelet transforms. We find that the cycle-averaged synodic rotation rate of strong magnetic flux can be written
as ω=13.47−2.58sin 2
θ or ω=13.45−2.06sin 2
θ−1.37sin 4
θ, where θ is the latitude. They agree well with the results derived from sunspots. A north–south asymmetry of the rotation rate is
found at high latitudes (28°<θ<40°). The strong flux in the southern hemisphere rotates faster than that in the northern hemisphere by 0.2 deg day−1. The asymmetry continued for cycles 21 – 23 and may be a secular property. 相似文献
15.
P. A. Sturrock 《Solar physics》2008,252(1):1-18
Time – frequency analysis of data from the GALLEX and GNO solar neutrino experiments shows that some features in power-spectrum
analyses of those datasets are due to aliasing (a result of the fact that run durations tend to be small multiples of one
week). Displays formed from the published GALLEX data show a sharp discontinuity that we attribute to some systematic effect.
We therefore normalize data for each of the four experiments in the GALLEX series and concatenate the resulting normalized
data. This step effectively removes the presumed systematic effect. To help understand the effect of aliasing, we form time – frequency
displays of the two principal modulations found in the data, at 11.87 year−1 and at 13.63 year−1. We also form time – frequency displays of datasets formed by subtracting these modulations from the actual (normalized)
data. The results suggest that the true principal modulation is that at 11.87 year−1. Comparison with helioseismology data suggests that modulation may be occurring in the core, perhaps resulting from inhomogeneities
and fluctuations in the nuclear-burning process, and that the sidereal rotation rate of the core is 12.87 year−1, or 408 nHz. 相似文献
16.
We report very high temporal and spectral resolution interferometric observations of some unusual solar radio bursts near
1420 MHz. These bursts were observed on 13 September 2005, 22 minutes after the peak of a GOES class X flare from the NOAA
region 10808. Our observations show 11 episodes of narrow-band intermittent emission within a span of ≈ 8 s. Each episode
shows a heavily frequency-modulated band of emission with a spectral slope of about −245.5 MHz s−1, comprising up to 8 individual blobs of emission and lasts for 10 – 15 ms. The blobs themselves have a spectral slope of
≈ 0 MHz s−1, are ≈ 200 – 250 kHz wide, appear every ≈ 400 kHz and last for ≈ 4 – 5 ms. These bursts show brightness temperatures in the
range 1012 K, which suggests a coherent emission mechanism. We believe these are the first high temporal and spectral resolution interferometric
observations of such rapid and narrow-bandwidth solar bursts close to 1420 MHz and present an analysis of their temporal and
spectral characteristics. 相似文献
17.
G. Trottet J.-P. Raulin G. Giménez de Castro T. Lüthi A. Caspi C. H. Mandrini M. L. Luoni P. Kaufmann 《Solar physics》2011,273(2):339-361
Solar flares observed in the 200 – 400 GHz radio domain may exhibit a slowly varying and time-extended component which follows
a short (few minutes) impulsive phase and can last for a few tens of minutes to more than one hour. The few examples discussed
in the literature indicate that such long-lasting submillimeter emission is most likely thermal bremsstrahlung. We present
a detailed analysis of the time-extended phase of the 27 October 2003 (M6.7) flare, combining 1 – 345 GHz total-flux radio
measurements with X-ray, EUV, and Hα observations. We find that the time-extended radio emission is, as expected, radiated
by thermal bremsstrahlung. Up to 230 GHz, it is entirely produced in the corona by hot and cool materials at 7 – 16 MK and
1 – 3 MK, respectively. At 345 GHz, there is an additional contribution from chromospheric material at a few 104 K. These results, which may also apply to other millimeter–submillimeter radio events, are not consistent with the expectations
from standard semiempirical models of the chromosphere and transition region during flares, which predict observable radio
emission from the chromosphere at all frequencies where the corona is transparent. 相似文献
18.
The properties of powerful (flux >10−19 W m−2 Hz−1) type III bursts observed in July – August 2002 by the radio telescope UTR-2 at frequencies 10 – 30 MHz are analyzed. Most
bursts have been registered when the active regions associated to these bursts were located near the central meridian or at
40° – 60° to the East or West from it. All powerful type III bursts drift from high to low frequencies with frequency drift
rates 1 – 2.5 MHz s−1. It is important to emphasize that according to our observations the drift rate is linearly increasing with frequency. The
duration of the bursts changes mainly from 6 s at frequency 30 MHz up to 12 s at 10 MHz. The instantaneous frequency bandwidth
does not depend on the day of observations, i.e. on the disk location of the source active region, and is increasing with frequency. 相似文献
19.
V. E. Abramov-Maximov G. B. Gelfreikh N. I. Kobanov K. Shibasaki S. A. Chupin 《Solar physics》2011,270(1):175-189
The nature of the three-minute and five-minute oscillations observed in sunspots is considered to be an effect of propagation
of magnetohydrodynamic (MHD) waves from the photosphere to the solar corona. However, the real modes of these waves and the
nature of the filters that result in rather narrow frequency bands of these modes are still far from being generally accepted,
in spite of a large amount of observational material obtained in a wide range of wave bands. The significance of this field
of research is based on the hope that local seismology can be used to find the structure of the solar atmosphere in magnetic
tubes of sunspots. We expect that substantial progress can be achieved by simultaneous observations of the sunspot oscillations
in different layers of the solar atmosphere in order to gain information on propagating waves. In this study we used a new
method that combines the results of an oscillation study made in optical and radio observations. The optical spectral measurements
in photospheric and chromospheric lines of the line-of-sight velocity were carried out at the Sayan Solar Observatory. The
radio maps of the Sun were obtained with the Nobeyama Radioheliograph at 1.76 cm. Radio sources associated with the sunspots
were analyzed to study the oscillation processes in the chromosphere – corona transition region in the layer with magnetic
field B=2000 G. A high level of instability of the oscillations in the optical and radio data was found. We used a wavelet analysis
for the spectra. The best similarities of the spectra of oscillations obtained by the two methods were detected in the three-minute
oscillations inside the sunspot umbra for the dates when the active regions were situated near the center of the solar disk.
A comparison of the wavelet spectra for optical and radio observations showed a time delay of about 50 seconds of the radio
results with respect to the optical ones. This implies an MHD wave traveling upward inside the umbral magnetic tube of the
sunspot. For the five-minute oscillations the similarity in spectral details could be found only for optical oscillations
at the chromospheric level in the umbral region or very close to it. The time delays seem to be similar. Besides three-minute
and five-minute ones, oscillations with longer periods (8 and 15 minutes) were detected in optical and radio records. Their
nature still requires further observational and theoretical study for even a preliminary discussion. 相似文献
20.
R. P. Kane 《Solar physics》2007,246(2):487-493
Three series (1876 – 1986, 1886 – 1996, and 1896 – 2006) of 111 annual values of sunspot number R
z in each were subjected to spectral analysis to detect periodicities by the maximum entropy method (MEM), and the periodicities
so obtained were used in a multiple regression analysis (MRA) to estimate the amplitudes and phases. All series showed roughly
similar spectra with many periodicities (24 or more), but most of these were insignificant. The significant periodicities
(far exceeding 2σ) were near 5, 8 – 12, 18, and 37 years. Using the amplitudes and phases of these, we obtained reconstructed series, which
showed good correlations (+ 0.7 and more) with the original series. When extrapolated further in time, the reconstructed series
indicated R
z(max) in the ranges 80 – 101 (mean 92) for cycle 24 during years 2011 – 2014, 112 – 127 (mean 119) for cycle 25 during years
2022 – 2023, 115 – 120 (mean 118) for cycle 26 during years 2032 – 2034, and 100 – 113 (mean 109) for cycle 27 during 2043 – 2045. 相似文献