172 research outputs found
Long-term variation in distribution of sunspot groups
We studied the relation between the distribution of sunspot groups and the
Gleissberg cycle. As the magnetic field is related to the area of the sunspot
groups, we used area-weighted sunspot group data. On the one hand, we confirm
the previously reported long-term cyclic behaviour of the sum of the northern
and southern sunspot group mean latitudes, although we found a somewhat longer
period (P~104 years). We introduced the difference between the ensemble average
area of sunspot groups for the two hemispheres, which turns out to show similar
behaviour. We also investigated a further aspect of the Gleissberg cycle where
while in the 19th century the consecutive Schwabe cycles are sharply separated
from each other, one century later the cycles overlap each other more and more.Comment: 4 page
Secular variation of hemispheric phase differences in the solar cycle
We investigate the phase difference of the sunspot cycles in the two
hemispheres and compare it with the latitudinal sunspot distribution. If the
north-south phase difference exhibits a long-term tendency, it should not be
regarded as a stochastic phenomenon.
We use datasets of historical sunspot records and drawings made by
Staudacher, Hamilton, Gimingham, Carrington, Spouml;rer, and Greenwich
observers, as well as the sunspot activity during the Maunder minimum
reconstructed by Ribes and Nesme-Ribes.
We employ cross-recurrence plots to analyse north-south phase differences. We
show that during the last 300 years, the persistence of phase-leading in one of
the hemispheres exhibits a secular variation. Changes from one hemisphere to
the other leading in phase were registered near 1928 and 1968 as well as two
historical ones near 1783 and 1875.
A long-term anticorrelation between the hemispheric phase differences in the
sunspot cycles and the latitudinal distribution of sunspots was traced since
1750.Comment: 7 pages, 4 figure
Multiple and changing cycles of active stars I. Methods of analysis and application to the solar cycles
Long-term observational data have information on the magnetic cycles of
active stars and that of the Sun. The changes in the activity of our central
star have basic effects on Earth, like variations in the global climate.
Therefore understanding the nature of these variations is extremely important.
The observed variations related to magnetic activity cannot be treated as
stationary periodic variations, therefore methods like Fourier transform or
different versions of periodogramms give only partial information on the nature
of the light variability. We demonstrate that time-frequency distributions
provide useful tools for analyzing the observations of active stars. With test
data we demonstrate that the observational noise has practically no effect on
the determination in the the long-term changes of time-series observations of
active stars. The rotational signal may modify the determined cycles, therefore
it is advisable to remove it from the data. Wavelets are less powerful in
recovering complex long-term changes than other distributions which are
discussed. Applying our technique to the sunspot data we find a complicated,
multi-scale evolution in the solar activity.Comment: Accepted to Astronomy and Astrophysic
Multi-timescale Solar Cycles and the Possible Implications
Based on analysis of the annual averaged relative sunspot number (ASN) during
1700 -- 2009, 3 kinds of solar cycles are confirmed: the well-known 11-yr cycle
(Schwabe cycle), 103-yr secular cycle (numbered as G1, G2, G3, and G4,
respectively since 1700); and 51.5-yr Cycle. From similarities, an
extrapolation of forthcoming solar cycles is made, and found that the solar
cycle 24 will be a relative long and weak Schwabe cycle, which may reach to its
apex around 2012-2014 in the vale between G3 and G4. Additionally, most Schwabe
cycles are asymmetric with rapidly rising-phases and slowly decay-phases. The
comparisons between ASN and the annual flare numbers with different GOES
classes (C-class, M-class, X-class, and super-flare, here super-flare is
defined as X10.0) and the annal averaged radio flux at frequency of 2.84
GHz indicate that solar flares have a tendency: the more powerful of the flare,
the later it takes place after the onset of the Schwabe cycle, and most
powerful flares take place in the decay phase of Schwabe cycle. Some
discussions on the origin of solar cycles are presented.Comment: 8 pages, 4 figure
Width of Sunspot Generating Zone and Reconstruction of Butterfly Diagram
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 SGZ. The
ratio of the sunspot number to the width of 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 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 (1998), the latitude distribution of sunspot groups ("the Maunder
butterfly diagram") for the 18th and the first half of the 19th centuries is
reconstructed and compared with historical sunspot observations.Comment: 16 pages, 11 figures; accepted by Solar Physics; the final
publication will be available at www.springerlink.co
Grand minima and maxima of solar activity: New observational constraints
Using a reconstruction of sunspot numbers stretching over multiple millennia,
we analyze the statistics of the occurrence of grand minima and maxima and set
new observational constraints on long-term solar and stellar dynamo models.
We present an updated reconstruction of sunspot number over multiple
millennia, from C data by means of a physics-based model, using an
updated model of the evolution of the solar open magnetic flux. A list of grand
minima and maxima of solar activity is presented for the Holocene (since 9500
BC) and the statistics of both the length of individual events as well as the
waiting time between them are analyzed.
The occurrence of grand minima/maxima is driven not by long-term cyclic
variability, but by a stochastic/chaotic process. The waiting time distribution
of the occurrence of grand minima/maxima deviates from an exponential
distribution, implying that these events tend to cluster together with long
event-free periods between the clusters. Two different types of grand minima
are observed: short (30--90 years) minima of Maunder type and long (110
years) minima of Sp\"orer type, implying that a deterministic behaviour of the
dynamo during a grand minimum defines its length. The duration of grand maxima
follows an exponential distribution, suggesting that the duration of a grand
maximum is determined by a random process.
These results set new observational constraints upon the long-term behaviour
of the solar dynamo.Comment: 10 Figure
Solar Grand Minima and random fluctuations in dynamo parameters
We consider to what extent the long-term dynamics of cyclic solar activity in
the form of Grand Minima can be associated with random fluctuations of the
parameters governing the solar dynamo. We consider fluctuations of the
alpha-coefficient in the conventional Parker migratory dynamo, and also in
slightly more sophisticated dynamo models, and demonstrate that they can mimic
the gross features of the phenomenon of the occurrence of Grand Minima over a
suitable parameter range. The temporal distribution of these Grand Minima
appears chaotic, with a more or less exponential waiting time distribution,
typical of Poisson processes. In contrast however, the available reconstruction
of Grand Minima statistics based on cosmogenic isotope data demonstrates
substantial deviations from this exponential law. We were unable to reproduce
the non-Poissonic tail of the waiting time distribution either in the framework
of a simple alpha-quenched Parker model, or in its straightforward
generalization, nor in simple models with feedback on the differential
rotation. We suggest that the disagreement may only be apparent and is
plausibly related to the limited observational data, and that the observations
and results of numerical modeling can be consistent and represent physically
similar dynamo regimes.Comment: Solar Physics, in prin
Long-term variations in the correlation between NAO and solar activity: the importance of North-South solar activity asymmetry for atmospheric circulation
General atmospheric circulation is the system of atmospheric motions over the
Earth on the scale of the whole globe. Two main types of circulation have been
identified: zonal - characterized by low amplitude waves in the troposphere
moving quickly from west to east, and meridional with stationary high amplitude
waves when the meridional transfer is intensified. The prevailing type of
circulation is related to global climate. Based on many years of observations,
certain circulation epochs have been defined when the same type of circulation
prevails for years or decades. Here we study the relation between long-term
changes in solar activity and prevailing type of atmospheric circulation, using
NAO index reconstructed for the last four centuries as a proxy for large-scale
atmospheric circulation. We find that when the southern solar hemisphere is
more active, increasing solar activity in the secular solar cycle results in
increasing zonality of the circulation, while when the northern solar
hemisphere is more active, increasing solar activity increases meridional
circulation. In an attempt to explain the observations, we compare the
short-term reaction of NAO and NAM indices to different solar drivers: powerful
solar flares, high speed solar wind streams, and magnetic cloudsComment: submitted to Advances in Space Research - a special issue with the
proceedings of The Second International Symposium on Space Climate:
"Long-term Change in the Sun, and its effects in the Heliosphere and Planet
Earth" - Sinaia, Romania, September 13-16, 200
The Maunder minimum (1645-1715) was indeed a grand minimum: a reassessment of multiple datasets
Aims.
Although the time of the Maunder minimum (1645–1715) is widely known as a period of extremely low solar activity, it is still being debated whether solar activity during that period might have been moderate or even higher than the current solar cycle (number 24). We have revisited all existing evidence and datasets, both direct and indirect, to assess the level of solar activity during the Maunder minimum.
Methods.
We discuss the East Asian naked-eye sunspot observations, the telescopic solar observations, the fraction of sunspot active days, the latitudinal extent of sunspot positions, auroral sightings at high latitudes, cosmogenic radionuclide data as well as solar eclipse observations for that period. We also consider peculiar features of the Sun (very strong hemispheric asymmetry of the sunspot location, unusual differential rotation and the lack of the K-corona) that imply a special mode of solar activity during the Maunder minimum.
Results.
The level of solar activity during the Maunder minimum is reassessed on the basis of all available datasets.
Conclusions.
We conclude that solar activity was indeed at an exceptionally low level during the Maunder minimum. Although the exact level is still unclear, it was definitely lower than during the Dalton minimum of around 1800 and significantly below that of the current solar cycle #24. Claims of a moderate-to-high level of solar activity during the Maunder minimum are rejected with a high confidence level
Patient Adherence to Tuberculosis Treatment: A Systematic Review of Qualitative Research
From a systematic review of qualitative research, Munro and coauthors found that a range of interacting factors can lead to patients deciding not to complete their course of tuberculosis treatment
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