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1.
O. S. Gopasyuk 《Kinematics and Physics of Celestial Bodies》2010,26(5):242-248
Torsional oscillations of seven single spots are studied based on the observations of the longitudinal magnetic field and
the field of radial velocities in the photospheric Fe I λ 525.3 nm line. The periods of umbra and penumbra oscillations are
2.2–7.1 and 3.3–7.7 days, respectively. The spots at a greater solar latitude are characterized by a longer period of oscillations
and a smaller axial strength of the magnetic field. The periods of umbra and penumbra oscillations increase with an increase
in the period and amplitude of the sunspot umbra oscillations. The obtained results can point to a unitary mechanism of torsional
oscillations of umbra and penumbra of single spots and a connection of these oscillations with the differential rotation of
the Sun. 相似文献
2.
The distribution of acoustic power over sunspots shows an enhanced absorption near the umbra – penumbra boundary. Previous
studies revealed that the region of enhanced absorption coincides with the region of strongest transverse potential field.
The aim of this paper is to i) utilize the high-resolution vector magnetograms derived using Hinode SOT/SP observations and study the relationship between the vector magnetic field and power absorption and ii) study the variation of power absorption in sunspot penumbrae due to the presence of spine-like radial structures. 相似文献
3.
A.-C. Donea D. Besliu-Ionescu P. S. Cally C. Lindsey V. V. Zharkova 《Solar physics》2006,239(1-2):113-135
Following the discovery of a few significant seismic sources at 6.0 mHz from the large solar flares of October 28 and 29,
2003, we have extended SOHO/MDI helioseismic observations to moderate M-class flares. We report the detection of seismic waves
emitted from the β γ δ active region NOAA 9608 on September 9, 2001. A quite impulsive solar flare of type M9.5 occurred from 20:40 to 20:48 UT.
We used helioseismic holography to image seismic emission from this flare into the solar interior and computed time series
of egression power maps in 2.0 mHz bands centered at 3.0 and 6.0 mHz. The 6.0 mHz images show an acoustic source associated
with the flare some 30 Mm across in the East – West direction and 15 Mm in the North – South direction nestled in the southern
penumbra of the main sunspot of AR 9608. This coincides closely with three white-light flare kernels that appear in the sunspot
penumbra. The close spatial correspondence between white-light and acoustic emission adds considerable weight to the hypothesis
that the acoustic emission is driven by heating of the lower photosphere. This is further supported by a rough hydromechanical
model of an acoustic transient driven by sudden heating of the low photosphere. Where direct heating of the low photosphere
by protons or high-energy electrons is unrealistic, the strong association between the acoustic source and co-spatial continuum
emission can be regarded as evidence supporting the back-warming hypothesis, in which the low photosphere is heated by radiation
from the overlying chromosphere. This is to say that a seismic source coincident with strong, sudden radiative emission in
the visible continuum spectrum indicates a photosphere sufficiently heated so as to contribute significantly to the continuum
emission observed. 相似文献
4.
The first statistical results in sunspot distributions in 1996–2004 obtained from the Solar Feature Catalogues (SFC) are presented.
A novel robust technique is developed for automated identification of sunspots on SOHO/MDI white-light (WL) full-disk solar
images. The technique applies image standardization procedures for elimination of the limb darkening and non-circular image
shape, uses edge-detection methods to find the sunspot candidates and their edges and morphological operations to smooth the
features and fill in gaps. The detected sunspots are verified with the SOHO/MDI magnetograms by strong magnetic fields being
present in sunspots. A number of physical and geometrical parameters of the detected sunspot features are extracted and stored
in the relational SFC database including umbra/penumbra masks in the form of run-length data encoding of sunspot bounding
rectangles. The detection results are verified by comparison with the manual daily detection results in Meudon and Locarno
Observatories in 2002 and by correlation (about 96%) with the 4 year sunspot areas produced manually at NOAA. Using the SFC
data, sunspot area distributions are presented in different phases of the solar cycle and hemispheres which reveals a periodicity
of the north–south asymmetry with a period of about 7–8 years. The number of sunspots increases exponentially with the area
decrease with the index slightly increasing from −1.15 (1997) to −1.34 (2001). 相似文献
5.
In this work we describe a technique developed to improve medium-term prediction methods of monthly smoothed sunspot numbers.
Each month, the predictions are updated using the last available observations (see the monthly output in real time at ). The improvement of the predictions is provided by applying an adaptive Kalman filter to the medium-term predictions obtained
by any other method, using the six-monthly mean values of sunspot numbers covering the six months between the last available
value of the 13-month running mean (the starting point for the predictions) and the “current time” (i.e. now). Our technique provides an effective estimate of the sunspot index at the current time. This estimate becomes the new
starting point for the updated prediction that is shifted six months ahead in comparison with the last available 13-month
running mean, and it provides an increase of prediction accuracy. Our technique has been tested on three medium-term prediction
methods that are currently in real-time operation: The McNish–Lincoln method (NGDC), the standard method (SIDC), and the combined
method (SIDC). With our technique, the prediction accuracy for the McNish–Lincoln method is increased by 17 – 30%, for the
standard method by 5 – 21% and for the combined method by 6 – 57%. 相似文献
6.
The distributions of sunspot longitude at first appearance and at disappearance display an east-west asymmetry that results
from a reduction in visibility as one moves from disk centre to the limb. To first order, this is explicable in terms of simple
geometrical foreshortening. However, the centre-to-limb visibility variation is much larger than that predicted by foreshortening.
Sunspot visibility is also known to be affected by the Wilson effect: the apparent ‘dish’ shape of the sunspot photosphere
caused by the temperature-dependent variation of the geometrical position of the τ=1 layer. In this article we investigate the role of the Wilson effect on the sunspot appearance distributions, deducing a
mean depth for the umbral τ=1 layer of 500 – 1500 km. This is based on the comparison of observations of sunspot longitude distribution and Monte Carlo
simulations of sunspot appearance using different models for spot growth rate, growth time and depth of Wilson depression. 相似文献
7.
We have estimated the upper and lower limits of sunspot activity, in terms of active day fraction during the Maunder minimum
(1645–1710), using raw information on individual daily observations (Hoyt and Schatten, 1998). Establishing the relation between
the sunspot activity and active day fraction after 1850, we evaluate the upper limit of annual group sunspot number during
the deep Maunder minimum (1645–1700) which does not exceed 4. The earlier finding of a dominant 22-year periodicity during
the Maunder minimum is verified and shown to be robust. Also we confirm that the start of the Maunder minimum was very abrupt. 相似文献
8.
We present the sunspot ideas and observations of the 18th century Portuguese scholar Teodoro de Almeida (1722 – 1804) and
Mexican scientist José Antonio Alzate (1737 – 1799). We describe the implications of dating a single sunspot observation performed
by Almeida in the early 1760s, during the maximum of cycle number 1. A possible solar cycle peak in 1760 (instead of 1761)
is investigated. We present several observations of sunspots obtained by Alzate during 1769 (partially associated with the
Venus and Mercury transits) and also on 20 July 1786. We estimate 100±34 as the Group Sunspot Number for this date. These
records were unknown and, therefore, not included in the database compiled by Hoyt and Schatten (1998). 相似文献
9.
R. P. Kane 《Solar physics》2007,243(2):205-217
For many purposes (e.g., satellite drag, operation of power grids on Earth, and satellite communication systems), predictions of the strength of
a solar cycle are needed. Predictions are made by using different methods, depending upon the characteristics of sunspot cycles.
However, the method most successful seems to be the precursor method by Ohl and his group, in which the geomagnetic activity
in the declining phase of a sunspot cycle is found to be well correlated with the sunspot maximum of the next cycle. In the
present communication, the method is illustrated by plotting the 12-month running means aa(min ) of the geomagnetic disturbance index aa near sunspot minimum versus the 12-month running means of the sunspot number Rz near sunspot maximum [aa(min ) versus Rz(max )], using data for sunspot cycles 9 – 18 to predict the Rz(max ) of cycle 19, using data for cycles 9 – 19 to predict Rz(max ) of cycle 20, and so on, and finally using data for cycles 9 – 23 to predict Rz(max ) of cycle 24, which is expected to occur in 2011 – 2012. The correlations were good (∼+0.90) and our preliminary predicted
Rz(max ) for cycle 24 is 142±24, though this can be regarded as an upper limit, since there are indications that solar minimum
may occur as late as March 2008. (Some workers have reported that the aa values before 1957 would have an error of 3 nT; if true, the revised estimate would be 124±26.) This result of the precursor
method is compared with several other predictions of cycle 24, which are in a very wide range (50 – 200), so that whatever
may be the final observed value, some method or other will be discredited, as happened in the case of cycle 23. 相似文献
10.
Based on the extended Greenwich – NOAA/USAF catalogue of sunspot groups, it is demonstrated that the parameters describing
the latitudinal width of the sunspot generating zone (SGZ) are closely related to the current level of solar activity, and
the growth of the activity leads to the expansion of the SGZ. The ratio of the sunspot number to the width of the SGZ shows
saturation at a certain level of the sunspot number, and above this level the increase of the activity takes place mostly
due to the expansion of the SGZ. It is shown that the mean latitudes of sunspots can be reconstructed from the amplitudes
of solar activity. Using the obtained relations and the group sunspot numbers by Hoyt and Schatten (Solar Phys.
179, 189, 1998), the latitude distribution of sunspot groups (“the Maunder butterfly diagram”) for the eighteenth and the first half of
the nineteenth centuries is reconstructed and compared with historical sunspot observations. 相似文献
11.
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
12.
R. P. Kane 《Solar physics》2006,236(1):207-226
After increasing almost monotonically from sunspot minimum, sunspot activity near maximum falters and remains in a narrow
grove for several tens of months. During the 2–3 years of turmoil near sunspot maximum, sunspots depict several peaks (Gnevyshev
peaks). The spaces between successive peaks are termed as Gnevyshev Gaps (GG). An examination showed that the depths of the troughs varied considerably from one GG to the next in the same cycle, with magnitudes varying in a wide range (<1%
to ∼20%). In any cycle, the sunspot patterns were dissimilar to those of other solar parameters, qualitatively as well as
quantitatively, indicating a general turbulence, affecting different solar parameters differently. The solar polar magnetic
field reversal does not occur at the beginning of the general turmoil; it occurs much later. For cosmic ray (CR) modulation
which occurs deep in the heliosphere, one would have thought that the solar open magnetic field flux would play a crucial
role, but observations show that the sunspot GGs are not reflected well in the solar open magnetic flux, where sometimes only
one peak occurred (hence no GG at all), not matching with any sunspot peak and with different peaks in the northern and southern
hemispheres (north – south asymmetry). Gaps are seen in interplanetary parameters but these do not match exactly with sunspot
GGs. For CR data available only for five cycles (19 – 23), there are CR gaps in some cycles, but the CR gaps do not match
perfectly with gaps in the solar open magnetic field flux or in interplanetary parameters or with sunspot GGs. Durations are
different and/or there are variable delays, and magnitudes of the sunspot GGs and CR gaps are not proportional. Solar polar
magnetic field reversal intervals do not coincide with either sunspot GGs or CR gaps, and some CR gaps start before magnetic field reversals, which should not happen if the magnetic field reversals are the cause of the CR gaps. 相似文献
13.
Thomas G. Moran Donald E. Jennings L. Drake Deming George H. McCabe Pedro V. Sada Robert J. Boyle 《Solar physics》2007,241(2):213-222
We present the first solar vector magnetogram constructed from measurements of infra-red Mg I 12.32-μm line spectra. Observations
were made at the McMath-Pierce Telescope using the Celeste spectrometer/polarimeter. Zeeman-split Stokes line spectra were
fitted with Seares profiles to obtain the magnetic field parameters. Maps of absolute field strength, line-of-sight angle,
and azimuth are presented. Analysis shows that the variation in field strength within a spatial resolution element, 2 arcseconds,
is greatest in the sunspot penumbra and that this is most likely caused by vertical field strength gradients, rather than
horizontal image smearing. Widths of the Zeeman-split σ components, assuming a formation layer thickness of 200 km, indicate that vertical field strength gradients can be as large
as 6.5 G/km in a penumbra. 相似文献
14.
Fluctuations of Solar Activity during the Declining Phase of the 11-Year Sunspot Cycle 总被引：1，自引：0，他引：1
R. P. Kane 《Solar physics》2009,255(1):163-168
The number of coronal mass ejections (CMEs) erupting from the Sun follows a trend similar to that of sunspot numbers during
the rising and maximum phase of the solar cycle. In the declining phase, the CME number has large fluctuations, dissimilar
to those of sunspot numbers. In several studies of solar – interplanetary and solar – terrestrial relationships, the sunspot
numbers and the 2800-MHz flux (F10) are used as representative of solar activity. In the rising phase, this may be adequate,
but in the declining phase, solar parameters such as CMEs may have a different behaviour. Cosmic-ray Forbush decreases may
occur even when sunspot activity is low. Therefore, when studying the solar influence on the Earth, one has to consider that
although geomagnetic conditions at solar maximum will be disturbed, conditions at solar minimum may not be necessarily quiet. 相似文献
15.
Historical sunspot records were analyzed by means of nonlinear tools to find synchronization phenomena at different time scales
on the Sun. Using cross-recurrence plots it is shown that the north – south sunspot synchronization demonstrates a set of
distinct periodic oscillations – 43.29, 18.52, and 7.63 years. Also we have traced the sunspot synchronization on shorter
time scales. Very rare and episodic synchronization within half of the Carrington rotation rate was detected. By using the
empirical mode decomposition technique the north – south sunspot time series were decomposed into intrinsic oscillatory modes.
To determine which modes of the signal are responsible for synchronization we separated them into high- and low-frequency
parts. It is shown that phase synchronization is detected only in the low-frequency modes. The high-frequency component demonstrates
noisy behavior with amplitude synchronization and strong phase mixing. 相似文献
16.
N.I. Kobanov 《Solar physics》2000,196(1):129-135
It is suggested that the problem of the extent of the outer penumbra could be considered by investigating the range over which the influence of the penumbra on the oscillation regime of the surrounding medium extends. In summer 1998, velocity oscillations were observed in the vicinities of the penumbra of the NOAA 8263 sunspot. The observations were carried out in the H line (chromosphere) and in the far wing of Nii 4857.2 Å (lower photosphere) simultaneously. The oscillation regime typical for sunspot penumbrae is observed within distances of about 15 from the visible outer boundary of the penumbra. 相似文献
17.
The observed phase relations between the weak background solar magnetic (poloidal) field and strong magnetic field associated
with sunspots (toroidal field) measured at different latitudes are presented. For measurements of the solar magnetic field
(SMF) the low-resolution images obtained from Wilcox Solar Observatory are used and the sunspot magnetic field was taken from
the Solar Feature Catalogues utilizing the SOHO/MDI full-disk magnetograms. The quasi-3D latitudinal distributions of sunspot
areas and magnetic fields obtained for 30 latitudinal bands (15 in the northern hemisphere and 15 in the southern hemisphere)
within fixed longitudinal strips are correlated with those of the background SMF. The sunspot areas in all latitudinal zones
(averaged with a sliding one-year filter) reveal a strong positive correlation with the absolute SMF in the same zone appearing
first with a zero time lag and repeating with a two- to three-year lag through the whole period of observations. The residuals
of the sunspot areas averaged over one year and those over four years are also shown to have a well defined periodic structure
visible in every two – three years close to one-quarter cycle with the maxima occurring at − 40° and + 40° and drifts during
this period either toward the equator or the poles depending on the latitude of sunspot occurrence. This phase relation between
poloidal and toroidal field throughout the whole cycle is discussed in association with both the symmetric and asymmetric
components of the background SMF and relevant predictions by the solar dynamo models. 相似文献
18.
Precursor techniques, in particular those using geomagnetic indices, often are used in the prediction of the maximum amplitude
for a sunspot cycle. Here, the year 2008 is taken as being the sunspot minimum year for cycle 24. Based on the average aa index value for the year of the sunspot minimum and the preceding four years, we estimate the expected annual maximum amplitude
for cycle 24 to be about 92.8±19.6 (1-sigma accuracy), indicating a somewhat weaker cycle 24 as compared to cycles 21 – 23.
Presuming a smoothed monthly mean sunspot number minimum in August 2008, a smoothed monthly mean sunspot number maximum is
expected about October 2012±4 months (1-sigma accuracy). 相似文献
19.
Using a magnetograph, we examine four sunspots for evidence of a magnetic canopy at the penumbra/photosphere boundary. The penumbral edge is determined from the photometric intensity and is defined to correspond to the value of the average intensity minus twice the standard deviation from the average. From a comparison of the location of this boundary with the location of contours of the vertical and horizontal components of the magnetic field, we conclude that the data are best represented by canopy-type fields close to all four sunspots. There is some evidence that the magnetic inclination in the canopies is 5°–15° with respect to the horizontal and that the canopy base height lies in the middle/upper photosphere. The observations further suggest that the magnetic canopy of a sunspot begins at its outer penumbral boundary. 相似文献
20.
A white-light flare (WLF) on 10 March 2001 was well observed in the Hα line and the Ca ii λ8542 line using the imaging spectrograph installed on the Solar Tower Telescope of Nanjing University. Three small sunspots
appeared in the infrared continuum image. In one sunspot, the infrared continuum is enhanced by 4–6% compared to the preflare
value, making the sunspot almost disappear in the continuum image for about 3 min. A hard X-ray (HXR) source appeared near
the sunspot, the flux of which showed a good time correlation with the profile of the continuum emission. In the sunspot region,
both positive and negative magnetic flux suffered a substantial change. We propose that electron precipitation followed by
radiative back-warming may play the chief role in heating the sunspot. The temperature rise in the lower atmosphere and the
corresponding energy requirement are estimated. The results show that the energy released in a typical WLF is sufficient to
power the sunspot heating. 相似文献