140 research outputs found
Long-Term Variations in Sunspot Characteristics
Relative variations in the number of sunspots and sunspot groups in activity
cycles have been analyzed based on data from the Kislovodsk Mountain
Astronomical Station and international indices. The following regularities have
been established: (1) The relative fraction of small sunspots decreases
linearly and that of large sunspots increase with increasing activity cycle
amplitude. (2) The variation in the average number of sunspots in one group has
a trend, and this number decreased from 12 in cycle 19 to 7.5 in cycle 24. (3)
The ratio of the sunspot index (Ri) to the sunspot group number index (Ggr)
varies with a period of about 100 years. (4) An analysis of the sunspot group
number index (Ggr) from 1610 indicates that the Gnevyshev-Ohl rule reverses at
the minimums of secular activity cycles. (5) The ratio of the total sunspot
area to the umbra area shows a long-term variation with a period about eight
cycles and minimum in cycles 16-17. (6) It has been indicated that the magnetic
field intensity and sunspot area in the current cycle are related to the
amplitude of the next activity cycle.Comment: 7 pages; 6 figure
Secular variations in the solar corona shape according to observations during a solar activity minimum epoch
Analysis of the solar corona structure during the periods of minimum solar
activity from 1867 till 2006 has been carried out. A new flattening index for
the large coronal streamers has been proposed. It has been shown that the index
has been smoothly changing during the last 140 years. The minimal value of the
index occurred during activity cycles 17--19; this was the period when the
solar corona most of all corresponded to the dipole configuration of the global
magnetic field of the Sun. At the beginning of the 20th and the 21st centuries,
the corona structure corresponded to the quadrupole configuration. The reasons
for the variations in the solar corona structure and its relation to
geomagnetic activity are discussed.Comment: 8 pages, 7 figures, 1 table. In proceedings 10-th Pulkovo conference
on solar physics,St.Petersburg-200
Some notes concerning the prediction of the amplitude of the two solar activity cycles
The parameter G, which is determined from the general number of sunspots
groups Ng according to the daily observations G=Sum(1/Ng)^2, is offered. This
parameter is calculated for the days when there is at least one sunspots group.
It characterizes the minimum epoch solar activity. Parameter G mounts to the
maximum during the epoch close to the minimal activity of sunspots. According
too the data of the sequence of sunspots group in Greenwich-USAF/NOAA
observatory format, observation data of Kislovodsk solar station and also daily
Wolf number the changes of parameter G during 100 years were reconstructed. It
is demonstrated in the paper that parameter G's amplitude in minimal solar
activity n is linked with the sunspot cycle's amplitude Wn+1. The 24th activity
cycle prediction is calculated, which makes W24=135(+/-12).Comment: 5 pages, 5 figure
Segmentation of coronal holes in solar disk images with a convolutional neural network
Current coronal holes segmentation methods typically rely on image
thresholding and require non-trivial image pre- and post-processing. We have
trained a neural network that accurately isolates CHs from SDO/AIA 193 Angstrom
solar disk images without additional complicated steps. We compare results with
publicly available catalogues of CHs and demonstrate stability of the neural
network approach. In our opinion, this approach can outperform hand-engineered
solar image analysis and will have a wide application to solar data. In
particular, we investigate long-term variations of CH indices within the solar
cycle 24 and observe increasing of CH areas in about three times from minimal
values in the maximum of the solar cycle to maximal values during the declining
phase of the solar cycle
Latitude of Ephemeral Regions as Indicator of Strength of Solar Cycles
Digitized images of full disk CaK spectroheliograms from two solar
observatories were used to study cycle variation of ephemeral regions (ERs)
over ten solar cycles 14-23. We calculate monthly averaged unsigned latitude of
ERs and compare it with annual sunspot number. We find that average latitude of
ERs can be used as a predictor for strength of solar cycle. For a short-term
prediction (dT about 1-2 years), maximum latitude of ephemeral regions (in
current cycle) defines the amplitude of that cycle (higher is the latitude of
ERs, larger are the amplitudes of sunspot cycle). For a long-term prediction
(dT about 1.5 solar cycles), latitude of ERs at declining phase of n-th cycle
determines the amplitude of (n+2)-th sunspot cycle (lower is the latitude of
ERs, stronger is the cycle). Using this latter dependency, we forecast the
amplitude of sunspot cycle 24 at W=92 +/- 13 (in units of annual sunspot
number).Comment: Memorie della Societ\`a Astronomica Italiana, in pres
Bimodal Distribution of Magnetic Fields and Areas of Sunspots
We applied automatic identification of sunspot umbrae and penumbrae to daily
observations from the Helioseismic Magnetic Imager (HMI) on board the Solar
Dynamics Observatory (SDO) to study their magnetic flux (B) and area (A). The
results confirm a previously known logarithmic relationship between the area of
sunspots and their maximum flux density. In addition, we find that the relation
between average magnetic flux (Bavg) and sunspot area shows a bimodal
distribution: for small sunspots and pores (A < 20 millionth of solar
hemisphere, MSH), Bavg = 800 G (gauss), and for large sunspots (A > 100 MSH),
Bavg is about 600 G. For intermediate sunspots, average flux density linearly
decreases from about 800 G to 600 G. A similar bimodal distribution was found
in several other integral parameters of sunspots. We show that this bimodality
can be related to different stages of sunspot penumbra formation and can be
explained by the difference in average inclination of magnetic fields at the
periphery of small and large sunspots.Comment: 13 pages, 5 figures, accepted for publication in Solar Physic
Search for relationship between duration of the extended solar cycles and amplitude of sunspot cycle
Duration of the extended solar cycles is taken into the consideration. The beginning of cycles is counted from the moment of polarity reversal of large-scale magnetic field in high latitudes, occurring in the sunspot cycle n till the minimum of the cycle n+2. The connection between cycle duration and its amplitude is established. Duration of the "latent" period of evolution of extended cycle between reversals and a minimum of the current sunspot cycle is entered. It is shown, that the latent period of cycles evolution is connected with the next sunspot cycle amplitude and can be used for the prognosis of a level and time of a sunspot maximum. The 24-th activity cycle prognosis is done. Long-term behavior of extended cycle's lengths is considered
A new dynamo pattern revealed by the tilt angle of bipolar sunspot groups
We obtain the latitude-time distribution of the averaged tilt angle of solar
bipoles. For large bipoles, which are mainly bipolar sunspot groups, the
spatially averaged tilt angle is positive in the Northern solar hemisphere and
negative in the Southern, with modest variations during course of the solar
cycle. We consider the averaged tilt angle to be a tracer for a crucial element
of the solar dynamo, i.e. the regeneration rate of poloidal large-scale
magnetic field from toroidal. The value of the tilt obtained crudely
corresponds to a regeneration factor corresponding to about 10% of r.m.s.
velocity of solar convection. These results develop findings of Kosovichev and
Stenflo (2012) concerning Joy's law, and agree with the usual expectations of
solar dynamo theory. Quite surprisingly, we find a pronounced deviation from
these properties for smaller bipoles, which are mainly solar ephemeral regions.
They possess tilt angles of approximately the same absolute value, but of
opposite sign compared to that of the large bipoles. Of course, the tilt data
for small bipoles are less well determined than those for large bipoles;
however they remain robust under various modifications of the data processing.Comment: 10 pages, 16 figures. Revised version accepted for publication in
MNRA
Tilt Angles of Solar Filaments over the Period 1919-2014
The spatial and temporal distributions of solar filaments were analyzed using
data from the Meudon Observatory for the period 1919-2003 and the Kislovodsk
Mountain Astronomical Station for the period 1979-2014. We scanned
solar synoptic charts on which the filaments were isolated and digitized. The
data on each filament comprise its location, length, area, and other
geometrical characteristics. The temporal distributions of the number and total
length of the filaments have been obtained. We also found latitudinal migration
of filament locations with the solar cycle, and analyzed the longitudinal
distribution and asymmetry of filaments in the northern and southern
hemispheres, and other properties of their distribution.
The tilt angles of filaments with respect the solar equator () were
analyzed. On average, the eastern tips of filaments are closer to the poles
than the western ones (). On the other hand, the filaments
in the polar regions (, where is the latitude)
usually have negative tilts (). The tilt angles vary with the
phases of the 11 year sunspot cycle and are at their highest values in the
epoch of the activity maximum. In the century-long modulation of the solar
activity (Gleissberg cycle), the mean tilt angles of filaments in the
mid-latitude zone () were maximum in the middle of
the 20th century in solar sunspot cycles 18-19. We hereby propose using the
statistical properties of solar filaments as an additional coherent measure of
manifestation of the solar cycle which covers all latitudes and for which
almost a century long systematically calibrated data series is available.Comment: 10 pages, 13 figure
Correlation Between Sunspot Number and ca II K Emission Index
Long-term synoptic observations in the resonance line of Ca II K constitute a
fundamental database for a variety of retrospective analyses of the state of
the solar magnetism. Synoptic Ca II K observations began in late 1904 at the
Kodaikanal Observatory, in India. In early 1970s, the National Solar
Observatory (NSO) at Sacramento Peak (USA) started a new program of daily
Sun-as-a-star observations in the Ca II K line. Today the NSO is continuing
these observations through its Synoptic Optical Long-term Investigations of the
Sun (SOLIS) facility. These different data sets can be combined into a single
disk-integrated Ca II K index time series that describes the average properties
of the chromospheric emission over several solar cycles. We present such a Ca
II K composite and discuss its correlation with the new entirely revised
sunspot number data series. For this preliminary investigation, the scaling
factor between pairs of time series was determined assuming a simple linear
model for the relationship between the monthly mean values during the duration
of overlapping observations.Comment: 16 pages, 8 figures, accepted for publication in Solar Physic
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